JP2002324945A - Optical communication system - Google Patents

Abstract

(57) [Problem] To use a surface-emitting type semiconductor laser device chip capable of lowering an operating voltage, an oscillation threshold current and the like as a light-emitting light source,
By increasing the fiber cable length of the surface emitting type semiconductor laser device chip or the optical fiber cable drawn from the module package containing the chip to a certain length or more, it is possible to improve the productivity of the assembly production of the package and easily. An object of the present invention is to make it possible to construct an optical communication system. On An n-GaAs substrate 2, n-semiconductor distributed to form a Bragg reflector 3, the thickness of lambda / 4 on the _{n-Ga x In-1 x} P y As 1-y layer 11 Were laminated. An undoped lower GaAs spacer layer 4, an active layer (quantum well active layer) 12, which is a three-layer Ga _x In _1-x As quantum well layer, and a GaAs barrier layer (20) are formed thereon.
nm) 13 and an undoped upper GaAs spacer layer 4 are laminated to form a resonator having a thickness of one oscillation wavelength λ (thickness of λ) in the medium. I have.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used for optical communication and the like and an optical communication system therefor.
More specifically, the present invention relates to an optical communication system in which a plurality of laser elements are formed using a so-called surface-emitting laser that emits light in a direction perpendicular to a semiconductor substrate surface used for manufacturing a semiconductor laser, thereby enabling large-capacity communication. Things.

[0002]

2. Description of the Related Art A surface emitting semiconductor laser emits laser light in a vertical direction from the surface of a substrate, so that two-dimensional parallel integration is possible, and the spread angle of the output light is relatively narrow (about 10 degrees). Therefore, it is easy to couple with an optical fiber and easy to inspect the element.
Therefore, in particular, development as an element suitable for configuring an optical transmission module (optical interconnection device) of a parallel transmission type has been actively conducted. The immediate application of the optical interconnection device is parallel connection between housings of computers and the like and between boards, as well as short-distance optical fiber communication, but large-scale computer networks and long distances are expected applications in the future. There is a trunk system for distance and large-capacity communication. Generally, a surface emitting semiconductor laser is made of GaAs or Ga.
Although it is common to comprise an active layer made of InAs, an upper semiconductor distributed Bragg reflector arranged above and below the active layer, and an optical resonator composed of a lower semiconductor distributed Bragg reflector on the substrate side. Since the length of the optical resonator is significantly shorter than that of the edge emitting semiconductor laser,
By setting the reflectivity of the reflecting mirror to an extremely high value (99% or more), it is necessary to easily cause laser oscillation. For this reason, a semiconductor distributed Bragg reflector formed by alternately laminating a low-refractive-index material made of AlAs and a high-refractive-index material made of GaAs at a period of １ ／ wavelength is usually used.

By the way, as described above, a long wavelength band laser having a laser wavelength of 1.1 μm or more used for optical communication, for example, a long wavelength band having a laser wavelength of 1.3 μm or 1.55 μm. In the laser, InP is used for the production substrate and InGaAsP is used for the active layer. However, the lattice constant of InP of the substrate is large, and a reflective mirror material matching the substrate cannot obtain a large refractive index difference. Must be more than pairs. Another problem with the semiconductor laser formed on the InP substrate is that the characteristics greatly change with temperature. For this reason, it is necessary to add a device for keeping the temperature constant, and it is difficult to use the device for general purposes such as consumer use. Light emitting semiconductors have not yet been put to practical use. As an invention made to solve such a problem, Japanese Patent Application Laid-Open No. 9-237942 has been proposed.
The one disclosed in Japanese Patent Application Laid-Open Publication No. H10-260, 1993 is known. According to this, a GaAs substrate is used as a production substrate, and a semiconductor layer made of AlInP that can be lattice-matched with the substrate is used as a low refractive index layer of at least one of the semiconductor distributed Bragg reflectors in the lower upper portion on the substrate side. G is applied to at least one of the lower and upper semiconductor distributed Bragg reflectors in the high refractive index layer.
The purpose of the present invention is to realize a semiconductor Bragg reflector having a high reflectivity with a small number of layers by using a semiconductor layer made of aInNAs so as to obtain a larger refractive index difference than before. GaInNAs is used as a material for the active layer. This is because the band gap (forbidden band width) can be reduced from 1.4 eV to 0 eV by increasing the N composition, and therefore, it can be used as a material that emits a wavelength longer than 0.85 μm. Because it becomes. In addition, it mentions that a semiconductor layer made of GaInNAs is preferable as a material for a long-wavelength surface emitting semiconductor laser in a 1.3 μm band and a 1.55 μm band because lattice matching with a GaAs substrate is possible.

[0004] However, in the past, only suggesting the possibility of realizing a surface emitting semiconductor laser in a wavelength band longer than 0.85 µm, such a thing has not been actually realized. This is because, although the basic configuration is almost theoretically determined, a more specific configuration for actually obtaining stable laser emission is still unknown. As an example, as described above, Al
A semiconductor distributed Bragg reflector formed by alternately laminating a low-refractive-index material composed of As and a high-refractive-index material composed of GaAs at a period of 1/4 wavelength;
Alternatively, as disclosed in Japanese Unexamined Patent Publication No. 9-237942, a semiconductor distributed Bragg reflector using a low refractive index layer made of a semiconductor layer made of AlInP that can be lattice-matched with the substrate has no laser element. No light was emitted, or even if light was emitted, its luminous efficiency was low, far from a practical level. This is because a material containing Al is chemically very active and crystal defects caused by Al are likely to occur. To solve this problem, Japanese Patent Application Laid-Open Nos. 8-340146 and 7-307 disclose the method.
There is a proposal for forming a semiconductor distributed Bragg reflector from GaInNP and GaAs that do not contain Al as in the invention disclosed in Japanese Patent No. 525. However, GaInNP
The refractive index difference between AlAs and GaAs is about half the refractive index difference between AlAs and GaAs. That is, at present, optical fiber communication is expected in computer networks and the like.
There is no long-wavelength surface-emitting semiconductor laser having a wavelength of 1.7 μm and a communication system using the same.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention has a laser oscillation wavelength of 1.
The present invention relates to a long-wavelength surface emitting semiconductor laser having a wavelength of 1 μm to 1.7 μm and an optical communication system thereof.
The purpose is to use a surface-emitting type semiconductor laser device chip that can lower the operating voltage, oscillation threshold current, etc. as a light emitting light source,
An object of the present invention is to propose an optical communication system which has low power consumption, has a small number of parts, and enables good optical coupling efficiency.
A second object is to use a long-wavelength surface emitting semiconductor laser device chip having a laser oscillation wavelength of 1.1 μm to 1.7 μm which can be used stably as a light emitting light source, and has high reliability and practicality. It is an object of the present invention to propose an optical communication system which has low optical coupling and enables good optical coupling efficiency. A third object of the present invention is to propose a good optical coupling efficiency at a low cost with a large alignment margin in such an optical communication system. The fourth purpose is
It is to propose high reliability in such an optical communication system. A fifth object is to propose a large-capacity optical communication system in such an optical communication system.

[0006]

According to the present invention, there is provided a laser chip and an optical communication system connected to the laser chip, wherein the laser chip has an oscillation wavelength of 1.1 μm. To 1.7 μm, and the main elements of the active layer that generates light are Ga, In, N, and As.
Or a layer of Ga, In, As, and a surface-emitting type semiconductor laser device chip having a resonator structure including reflectors provided above and below the active layer in order to obtain a laser beam. The reflective mirror has a reflection wavelength of 1.1 μm or more, the refractive index of a material layer constituting the reflective mirror periodically changes to a value different from a small value, and a semiconductor distributed Bragg reflection that reflects incident light by light wave interference. with a mirror, the material layer of the refractive index is small is _Al x _{Ga 1-x} as
(0 <x ≦ 1), and the material layer having a large refractive index is Al _{y
Ga 1-y As (0 ≦} y <x ≦ 1) and then, and the the refractive index between the refractive index is small and large material layer has a value between the small and large _Al z _{Ga 1-z} As The light emitting source is a surface-emitting type semiconductor laser device chip which is a reflector having a heterospike buffer layer of (0 ≦ y <z <x ≦ 1) with a thickness of 20 nm to 50 nm. Assuming that the core diameter X of the fiber or the optical waveguide, the aperture diameter d of the semiconductor laser, and the light emission angle θ of the semiconductor laser, the optical path length l from the semiconductor laser to the end of the optical fiber or the optical waveguide is d + 2 tan.
(Θ / 2) ≦ X is satisfied.

In fields where the laser oscillation wavelength is expected to be 1.1 μm to 1.7 μm for optical fiber communication, such as computer networks and trunk systems for long-distance large-capacity communication, the operating voltage, oscillation threshold current and the like are reduced. Although there was no surface emitting semiconductor laser capable of generating stable laser oscillation with little heat generation from the laser element and a communication system using the same, the operating voltage was improved by devising a semiconductor distributed Bragg reflector as in the present invention. In addition, the oscillation threshold current and the like can be reduced, the laser element generates less heat, stable oscillation can be achieved, and a low-cost practical optical communication system can be realized. Further, compared to the case of using a conventional edge emitting laser, by using a surface emitting semiconductor laser capable of lowering the operating voltage and the oscillation threshold current as in the present invention, an optical communication system with low power consumption can be realized. Further, in the case of the conventional edge emitting semiconductor laser, it is necessary to insert a lens optical system between the semiconductor laser and the optical fiber or the optical waveguide. By adopting the above positional relationship, it is not necessary to use a lens, so that the number of parts is small, the alignment is loose in the optical axis direction, and good optical coupling efficiency with the optical fiber or the optical waveguide can be realized. According to the invention, by devising a semiconductor distributed Bragg reflector, an operating voltage, an oscillation threshold current, and the like can be reduced, a stable oscillation can be performed with less heat generation of a laser element, and a low-cost practical optical communication system Was realized. In addition, by using a surface-emitting type semiconductor laser capable of reducing operating voltage, oscillation threshold current, and the like, an optical communication system with low power consumption can be realized, and further, by setting the positional relationship between the semiconductor laser and an optical fiber or an optical waveguide. ,
Since there is no need to use a lens, the number of parts is small, alignment is gradual in the optical axis direction, and good optical coupling efficiency with an optical fiber or an optical waveguide can be realized.

A second aspect of the present invention is a laser chip and an optical communication system connected to the laser chip, wherein the laser chip has an oscillation wavelength of 1.1 μm to 1.7 μm, and a main element of an active layer for generating light is a main element. A layer made of Ga, In, N, As or a layer made of Ga, In, As,
A surface-emitting type semiconductor laser device chip having a resonator structure including a reflector provided above and below the active layer to obtain a laser beam, wherein the reflector has a reflection wavelength of 1.1 μm or more. The semiconductor layer is a distributed Bragg reflector in which the refractive index of the material layer constituting the semiconductor layer periodically changes to a value different from a small value and reflects incident light by light wave interference, and the material layer having a small refractive index is Al _x Ga. _{1− x} As (0 <x
≦ 1), and the material layer having a large refractive index is Al _y Ga
_1-y As (0 ≦ y <x ≦ 1), wherein the main composition between the active layer and the reflector is Ga _x In
_A surface-emitting type semiconductor laser device chip provided with a non-radiative recombination preventing layer composed of _{1-x Py} As _1-y (0 <x ≦ 1, 0 <y ≦ 1) layers is used as a light emitting light source. , The core diameter X of the optical fiber or the optical waveguide, the aperture diameter d of the semiconductor laser, and the light emission angle θ of the semiconductor laser, the optical path length l from the semiconductor laser to the end of the optical fiber or the optical waveguide is d +
It is characterized by satisfying 2ltan (θ / 2) ≦ X.
A long-wavelength surface emitting semiconductor laser that can be used stably in the field of laser oscillation wavelengths of 1.1 μm to 1.7 μm where optical fiber communication is expected, such as computer networks and trunk lines for long-distance large-capacity communication. And there was no communication system using the same. However, as in the present invention, a surface-emitting type semiconductor laser device chip provided with a non-radiative recombination prevention layer enables stable oscillation, A practical optical communication system as a light source was realized. Further, in the case of the conventional edge emitting semiconductor laser, it was necessary to insert a lens optical system between the semiconductor laser and the optical fiber or the optical waveguide. By using a positional relationship, it is not necessary to use a lens, so that the number of components is small, alignment is loose in the optical axis direction, and good optical coupling efficiency with an optical fiber or an optical waveguide can be realized. According to the invention, stable oscillation can be achieved by using a surface emitting semiconductor laser device chip provided with a non-radiative recombination preventing layer, and a practical optical communication system using this as a light emitting light source can be realized. . In addition, by setting the positional relationship between the semiconductor laser and the optical fiber or the optical waveguide, there is no need to use a lens, so the number of components is small, alignment is loose in the optical axis direction, and good optical coupling efficiency with the optical fiber or the optical waveguide. Was realized.

According to a third aspect of the present invention, the semiconductor laser and the optical fiber or the optical waveguide are in contact with each other. According to such a technical means, in such an optical communication system, since the semiconductor laser and the optical fiber or the optical waveguide are in contact with each other, a lens optical system is not required, so that the number of parts is small and the direction orthogonal to the optical axis is reduced. Low cost because the alignment margin of
Good optical coupling efficiency with optical fiber or optical waveguide could be realized. According to a fourth aspect of the present invention, the optical fiber or the optical waveguide has a heat radiating portion, and the heat radiating portion is in contact with the semiconductor laser element chip. According to such a technical means, such an optical fiber or an optical waveguide has a heat radiating portion, and the heat radiating portion abuts on the semiconductor laser element chip, thereby transferring heat generated by the semiconductor laser emission to the substrate side. Since the heat can be dissipated not only from the light but also from the light emitting surface side, a more stable optical communication system can be realized. According to a fifth aspect of the present invention, a plurality of the optical fiber or the optical waveguide and the semiconductor laser device are provided. According to such technical means, parallel signal processing can be performed by using a plurality of such optical fibers or optical waveguides and surface emitting semiconductor laser devices, so that a larger capacity optical communication system can be realized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are not merely intended to limit the scope of the present invention but are merely illustrative examples unless otherwise specified. . First, the laser oscillation wavelength with a small transmission loss, which is a light emitting element applied to the optical communication system of the present invention, is as follows.
One example of a long-wavelength band surface emitting semiconductor laser of 1 μm to 1.7 μm will be described with reference to FIG. As described above, conventionally, the laser oscillation wavelength to be applied by the present invention is 1.
With respect to the long-wavelength surface emitting semiconductor laser having a wavelength of 1 μm to 1.7 μm, there is only a suggestion of the possibility, and a material for realizing the laser, and a more specific and detailed configuration were unknown. In the present invention, a material such as GaInNAs is used for the active layer, and a more specific configuration is clarified. The details are described below. In the present invention, n-G of plane orientation (100) is used.
On the aAs substrate 2, n-Al _x Ga having a thickness (thickness of λ / 4) １ ／ times the oscillation wavelength λ in each medium.
_{1-x As (x = 1.0} ) ( low refractive index layer-refractive index small layer) and _{n-Al y Ga 1-y} As (y = 0) ( high refractive index layer-refractive index large layer) alternately 35 cycles laminated n- semiconductor distributed Bragg reflector 3 (AlAs / GaAs lower semiconductor distributed Bragg reflector) is _{formed, n-Ga x in 1-} x P y of the thickness of lambda / 4 on the As _1-y (x = 0.
5, y = 1) Layer 11 was laminated. In this example n-Ga _{x
In 1-x P y As 1} -y (x = 0.5, y = 1) layer are also part of the lower reflecting mirror has a low refractive index layer (a layer having a refractive index is small).

Then, an undoped lower GaAs switch is formed thereon.
Pacer layer 4 and three layers of Ga_xIn_{1 -X}As quantum well layer
Active layer (quantum well active layer) 12 and GaAs barrier
A multiple quantum well active layer comprising a layer (20 nm) 13;
And an upper doped GaAs spacer layer,
Of the thickness of one oscillation wavelength λ (thickness of λ)
A resonator is formed. In addition, C (carbon)
P-Ga_xIn_1-xP_yAs_1-y(X = 0.
5, y = 1) layer and Zn-doped p-Al_xGa_1-xAs
(X = 0) is set to 1 of the oscillation wavelength λ in each medium.
/ 4 times the thickness of the periodic structure (one cycle) laminated alternately
Layer on which C-doped p-Al_xGa_1-xAs
(X = 0.9) and Zn-doped p-Al_xGa_1-xAs
(X = 0) is set to 1 of the oscillation wavelength λ in each medium.
With a periodic structure (25 periods) alternately stacked with a thickness of / 4 times
Semiconductor Bragg reflector 5 (Al_0.9Ga
_0.1As / GaAs upper semiconductor distributed Bragg reflector)
Is formed. In this example, p-Ga_xIn_1-xP _y
As_1-yThe (x = 0.5, y = 1) layer is also a part of the upper reflecting mirror.
And a low refractive index layer (a layer having a low refractive index).
Here, both the upper and lower mirrors have low refractive index layers.
(Low refractive index layer) / high refractive index layer (high refractive index layer) alternately
In the present invention, there is a refraction
Al with a ratio between small and large_zGa_1-zAs (0 ≦
providing a hetero-spike buffer layer consisting of y <z <x ≦ 1)
ing.

FIG. 2 shows a surface emitting semiconductor device applied to the present invention.
Reflector whose reflection wavelength of body laser is 1.1μm or more
This will be described more specifically. The reflection wavelength applied to the present invention is
In a reflecting mirror of 1.1 μm or more, a low refractive index layer (a low refractive index layer) is used.
Layer) and the high refractive index layer (high refractive index layer)
Hetero spike buffer layer Al with a value between_zGa
_1-zAs (0 ≦ y <z <x ≦ 1) 15 is provided.
Figure 2 shows a part of a semiconductor distributed Bragg reflector.
There is a figure (it is omitted in FIG. 1 because the figure is complicated)
are doing). Conventional semiconductor with laser wavelength 0.85μm band
With respect to the laser, such a heterospike buffer layer 15
It is being considered to establish
The material, its thickness, etc.
It has not been. Also, the laser oscillation wavelength as in the present invention is
1.1 μm to 1.7 μm long wavelength band surface emitting semiconductor laser
Is not considered at all. The reason is this field
(Long wavelength band whose laser oscillation wavelength is 1.1 μm to 1.7 μm
Surface emitting semiconductor lasers) is a new field, and it is still almost
This is because research has not progressed. The inventor is quick
In this field (the laser oscillation wavelength is 1.1 μm to 1.7 μm)
Long wavelength surface emitting semiconductor laser and optical communication using the same
Of the usefulness of shin) and intensive study to realize it
Was done.

The refractive index of the material layer of such a hetero-spike buffer layer changes continuously or stepwise by controlling the gas flow rate at the time of formation or by changing the Al composition continuously or stepwise. It is formed as follows. More _{specifically, Al z Ga 1-z As} (0
.Ltoreq.y <z <x.ltoreq.1) The layer is formed so that the value of z changes from 0 to 1.0, that is, the ratio of Al to Ga gradually changes, such as GaAs to AlGaAs to AlAs. This is created by controlling the gas flow during layer formation as described above. Further, it may be formed so that the ratio of Al and Ga changes continuously as described above, or the same effect can be obtained even if the ratio changes stepwise. The reason for providing such a heterospike buffer layer is to solve the problem that the electrical resistance of the p-semiconductor distributed Bragg reflector, which is one of the problems of the distributed Bragg reflector, is high. This is due to a hetero-barrier generated at the interface between the two types of semiconductor layers constituting the semiconductor distributed Bragg reflector. As the Al composition gradually changes to the other composition,
By changing the refractive index, it is possible to suppress the generation of the hetero barrier. Such a hetero spike buffer layer will be described more specifically. FIG. 3 shows an example of a semiconductor distributed Bragg reflector in which a hetero-spike buffer layer is provided between two types of semiconductor layers constituting the semiconductor distributed Bragg reflector. In the figure, as an example of the material of the semiconductor distributed Bragg reflector, an AlGaAs-based semiconductor material (Al _z
Ga _1-z As (0 ≦ y <z <x ≦ 1) is shown. The two kinds of semiconductor layers constituting the semiconductor distributed Bragg reflector are AlAs and GaAs, and AlAs and Ga
As a hetero-spike buffer layer having an intermediate valence band energy of As, a composition gradient layer in which the Al composition is changed is provided therebetween. _That, Al _{z Ga 1-z} As
(0 ≦ y <z <x ≦ 1) The value of z of the layer is changed from 0 to 1.0, that is, GaAs to AlGaAs to AlA.
The ratio of Al and Ga is gradually changed to s.

The AlGaAs-based semiconductor material has an increased band gap energy as the Al composition increases.
The refractive index decreases. At this time, in the conduction band, the energy starts to decrease until the Al composition reaches 0.43, but in the valence band, the valence band energy decreases monotonically in substantially proportion to the increase amount of the Al composition ( Overall, the bandgap energy increases with composition.) In addition to this, when an AlGaInP-based material is taken as an example, this material is a quaternary material, but shows the same tendency as the AlGaAs-based Al composition increases as the AlInP composition increases. The conduction band energy begins to decrease after increasing to an AlInP composition of 0.7. However, the valence band energy similarly decreases monotonically with increasing AlInP composition. In the example of FIG. 3, the composition gradient rate (increase rate of the band gap energy) of the region near the GaAs layer (region I in FIG. 3) is shown in FIG.
In region II), the composition gradient is larger than the composition gradient. For comparison, FIG. 4 shows a structure in which a linear composition gradient layer having a linearly changed Al composition is used as a hetero-spike buffer layer.

FIG. 5 is a graph showing the relationship between the reflection wavelength of 1.3 μm AlAs
It is a result of estimating the electric resistance of a 4-pair p-DBR in which the heterospike buffer layer of FIG. 3 having a thickness of 20 nm is provided at the GaAs interface. In FIG. 5, the carrier density of each layer of the DBR including the hetero-spike buffer layer is a P-type of 1E18 [cm ⁻³ ], and the vertical axis indicates the differential sheet resistance near zero bias. The abscissa indicates the Al composition gradient in the region I, and indicates the thickness of the different region I (shown in the figure). The sum of the region I and the region II is always 20 nm, and the thickness and the composition gradient of the region II are determined by the thickness of the region I and the composition gradient. Simply Ga
When the linear composition gradient layer is provided between the As layer and the AlAs layer, the Al composition gradient is 0.05 [nm ^-1 ], which corresponds to the point A in the figure. As shown in FIG. 5, by increasing the gradient of the Al composition in the region I, the resistance value is reduced as compared with the conventional case where the composition gradient is simply made linear. It can also be seen that there is an optimum Al composition gradient that is minimal. For example, the thickness of the region I is 10 nm.
(The same thickness as in the region II), the Al composition gradient was 0.09.
In [nm ^-1 ], the resistance is reduced to about 80% of the conventional ^value (this tendency does not depend on the applied voltage).

Next, the reason will be described. FIG.
FIG. 3 is a band diagram of a thermal equilibrium state of a DBR hetero interface made of AlAs / GaAs. As shown in the figure, heterospikes caused by band discontinuity mainly appear remarkably on the AlAs layer side having a large band gap, and almost no notch is generated on the GaAs layer side. The notch generated on the GaAs layer side does not originally cause a high resistance, so that the AlA
It is important to lower the resistance efficiently that spikes generated on the s layer side are efficiently flattened with a limited thickness of the hetero spike buffer layer. In the structure of FIG.
This corresponds to the fact that the composition is rapidly increased on the aAs side and the composition gradient on the AlAs side where spikes occur is gradually changed. This makes it possible to reduce the occurrence of spikes as compared with the case where the composition change of the hetero-spike buffer layer is simply linear (accordingly, when the Al composition gradient in the region I is smaller than that in the region II, the resistance value becomes smaller). Increases.). FIG. 7 is a schematic diagram of a band diagram in the thermal equilibrium state of FIG. Compared to the conventional simple composition gradient layer, A
The composition gradient on the lAs side can be reduced. From the above, it is understood that the electric resistance can be reduced as compared with the related art by increasing the composition gradient in the region I.
Then hetero spike buffer layer _{Al z Ga 1-z As (} 0 ≦ y of such a refractive index takes a value between the small and large <z <x ≦
The result of study on the optimum thickness of 1) will be described. FIG. 8 shows AlAs / Ga having a reflection center wavelength at 1.3 μm.
It is the result of calculating the differential electric resistivity near zero bias by changing the thickness of the hetero-spike buffer layer for the four-pair DBR using As. The doping density of the DBR layer is 1
E18cm ^{- 3} and then, doping density of each layer containing a hetero spike buffer layer are uniform. The value indicated by the broken line is the resistivity obtained from the bulk resistance of each semiconductor layer, and shows the resistivity of the DBR obtained when there is no influence from the hetero interface.

As shown in FIG. 8, no hetero-spike buffer layer is provided.
DBR (hetero spike buffer layer thickness 0) resistivity
Is 1Ωcm²Is very high resistance and a real problem
Through the DBR stacked by 20 pairs or more
The thing itself is difficult, and it is very expensive to further energize
Requires voltage. Therefore, a surface with such a DBR
It is difficult for a light emitting laser device to actually oscillate. I
However, when a 5 nm hetero-spike buffer layer is provided
In this case, compared to the case without a hetero spike buffer layer,
It is possible to reduce the resistivity by about two digits,
And the oscillation can be obtained. Change
In addition, since the voltage required for energization is also reduced,
Various problems related to reliability, such as obstacles, are greatly improved. Furthermore,
The resistivity increases sharply as the thickness of the heterospike buffer layer increases.
, And especially at 20 nm and above, the resistivity is almost
It has a constant value. FIG. 8 shows the heterospike buffer layer and each
The p-type doping density of the layer is 1E18 cm ^-3As uniform
This shows the structure in the case of doping. What
In addition, this doping concentration is a standard used for a DBR.
Value. In the structure of the DBR shown in FIG.
The thickness of the heterospike buffer layer that begins to saturate is about 20 nm
And the resistivity at this time is approximately 2.75 of the bulk resistivity.
The value is reduced to a very low value of about five times. That is,
The lower limit of the thickness of the terror spike buffer layer is set to 20 nm.
With the above thickness, the operating voltage of the element is set to the lowest value.
And the heat generation of the element can be minimized. Obedience
The temperature at which oscillation can be maintained, and the resulting optical output
Add. However, on the contrary, the optical characteristics of DBR
Reflectivity increases as the thickness of the heterospike buffer layer increases
There is a problem that the rate decreases. Fig. 9 shows heterospy
Like the decrease in reflectivity of the DBR to the change in the buffer layer thickness
The child is shown in detail. Compare with the straight line shown in the figure.
Then, the thickness of the hetero-spike buffer layer becomes 50 nm or more.
It can be seen that the rate of change in reflectance sharply increases. element
The oscillation threshold current starts to increase correspondingly.
Therefore, the upper limit of the thickness of the hetero spike buffer layer is 50 nm.
Is appropriate. As described above, 20 nm or more, 50
In a DBR provided with a heterospike buffer layer of nm or less,
Effective reduction of resistance due to hetero interface
In addition, a high reflectance can be obtained at the same time. This
In a surface emitting laser device using
Therefore, it is possible to easily obtain oscillation at a low threshold current.
You.

The laser oscillation wavelength of the present invention is 1.1 μm.
m to 1.7 μm long wavelength band surface emitting semiconductor laser,
The thickness is preferably from 20 nm to 50 nm. If the thickness is smaller than this, there is a problem that the resistance becomes large and current does not easily flow, the element generates heat, and the driving energy increases. When the thickness is large, the resistance becomes small, which is advantageous in terms of heat generation of the element and driving energy. However, there is a problem that the reflectance cannot be obtained this time, and as described above, the optimum range (20 nm to 5 nm) is obtained.
(Thickness of 0 nm). As described above, the provision of such a hetero-spike buffer layer for a conventional semiconductor laser having a laser wavelength in the 0.85 μm band has been studied.
In the case of a long-wavelength surface emitting semiconductor laser of 1 μm to 1.7 μm, it is more effective. This is because, for example, to obtain the same reflectance (for example, 99.5% or more), 0.85
In the case of the 1.1 μm to 1.7 μm band than the μm band, such a material layer can be approximately doubled, so that the resistance value of the semiconductor distributed Bragg reflector can be reduced and the operating voltage can be reduced. In addition, the oscillation threshold current and the like are reduced, which is advantageous in terms of prevention of heat generation of the laser element, stable oscillation, and low energy driving. In other words, providing such a hetero-spike buffer layer on a semiconductor distributed Bragg reflector is particularly effective for a long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm as in the present invention. It can be called a device. As an example of a more detailed study result for obtaining an effective reflectance, for example, in a 1.3 μm band surface emitting laser device, Al _x Ga _1-x As (x = 1.0) (low refractive index) rate layer-refractive index small layer) and _{Al y Ga 1-y as (} y
= 0) (in the case of a high refractive index layer-refractive index large layer) 20 period stacking, the reflectance of the semiconductor distributed Bragg reflector is 99.7% or less _{Al z Ga 1-z As (} 0 ≦ y
<Z <x ≦ 1) The thickness of the layer is 30 nm. The wavelength band where the reflectance is 99.5% or more is 53 nm,
When the reflectance is designed to be 99.5% or more, it is only necessary to control the film thickness by ± 2%. Therefore, when prototypes of 10 nm, 20 nm, and 30 nm which are equivalent to and thinner than this were prototyped, the reflectivity could be kept to a practically acceptable level, and the resistance value of the semiconductor distributed Bragg reflector could be reduced. A 1.3 μm band surface emitting laser device was realized, and laser oscillation was successful. Other configurations of the prototyped laser element are as described below.

In the multilayer mirror, there is a band having a high reflectance including a design wavelength (assuming that the film thickness can be completely controlled). It is referred to as a high-reflectance band (including a region where the reflectivity is equal to or more than a required value for a target wavelength). This is the region where the reflectance at the design wavelength is the highest and decreases very little as the wavelength increases. It drops off sharply from some area. Originally, it is necessary to completely control the film thickness of the multilayer mirror at the atomic layer level so that the reflectance is higher than the required reflectance for the target wavelength. But actually ± 1
Since a film thickness error of about% occurs, the target wavelength deviates from the wavelength having the highest reflectance. For example, if the target wavelength is 1.3
In the case of μm, when the film thickness control is shifted by 1%, the wavelength having the highest reflectance is shifted by 13 nm. Therefore, it is desirable that the band of the high reflectance (here, the region where the reflectance is equal to or more than a required value with respect to a target wavelength) is wide. As described above, in the long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm as in the present invention, the reflectivity is improved by devising and optimizing the configuration of such a semiconductor distributed Bragg reflector. The resistance value can be reduced while maintaining high, so that the operating voltage, oscillation threshold current, etc. can be reduced,
Prevention of heat generation of the laser element, stable oscillation, and low energy driving are possible.

Returning again to FIG. 1, the uppermost p-Al _x G
The a1 _- xAs (x = 0) layer also has a role as a contact layer (p-contact layer) for making contact with an electrode. Here, the In composition x of the quantum well active layer was 39% (Ga _0.61 In _0.39 As). The thickness of the quantum well active layer was 7 nm. The quantum well active layer had a compressive strain of about 2.8% with respect to the GaAs substrate. The entire surface emitting semiconductor laser was grown by MOCVD. In this case, no lattice relaxation was observed. The raw materials constituting each layer of the semiconductor laser include:
TMA (trimethylaluminum), TMG (trimethylgallium), TMI (trimethylindium), As
H ₃ (arsine) and PH ₃ (phosphine) were used.
H ₂ was used as a carrier gas. In the case where the strain is large as in the active layer (quantum well active layer) of the device shown in FIG. Here, Ga
The InAs layer (quantum well active layer) is grown at 550 ° C. The MOCVD method used here has a high degree of supersaturation and is suitable for crystal growth of a high strain active layer. In addition, high vacuum is not required as in the MBE method, and the supply flow rate and supply time of the source gas may be controlled.

In this example, a portion outside the current path was formed by irradiating protons (H ⁺ ) to form an insulating layer (high resistance portion) to form a current narrowing portion. In this example, a p-side electrode is formed on the p-contact layer which is the uppermost layer of the upper reflector and is a part of the upper reflector, excluding the light emitting portion, and an n-side electrode is formed on the back surface of the substrate. Was formed. In this example, in the active region (resonator including the upper and lower spacer layers and the multiple quantum well active layer in this embodiment) sandwiched between the upper and lower reflectors and into which carriers are injected and recombined, the active region has material containing al (percentage of group III 1% or more) without using a further layer closest to the active layer of the low refractive index layer of the lower and upper reflector _{Ga x in 1-x P y} As
_1-y (0 <x ≦ 1, 0 <y ≦ 1) as a non-radiative recombination preventing layer. That is, by appropriately selecting the value of x or y, GaInP, GaInPAs, or GaPAs is used as the non-radiative recombination preventing layer. Note that this layer, there is a case where a material other than Al is added small amount, the main _{material, Ga x In 1-x P} y As
_1-y (0 <x ≦ 1, 0 <y ≦ 1). The carriers are confined between the low-refractive index layers of the upper and lower reflectors, which are the wide gaps closest to the active layer, so that only the active region is an Al-free layer (1% of the group III).
However, if the low refractive index layer (wide gap layer) of the reflector in contact with the active region is made to contain Al even when the carrier is injected and recombined, non-radiative recombination occurs at this interface. Occurs and the luminous efficiency is reduced. Therefore, it is desirable that the active region be formed of a layer containing no Al. Also this main composition _{Ga x In 1-x P y} As
_The non-radiative recombination preventing layer made of _1-y (0 <x ≦ 1, 0 <y ≦ 1) has a lattice constant smaller than that of the GaAs substrate and has a tensile strain.

In the epitaxial growth, the information of the base is reflected
Crawling to the growth layer if there is a defect on the substrate surface
Going up. However, if there is a strained layer, crawling of such defects
It is known that rising is suppressed and there is an effect. Up
When the defect reaches the active layer, the luminous efficiency is reduced.
U. In addition, the critical thickness is required to be reduced for active layers with strain.
Problems such as the inability to grow a layer having a large thickness occur. Especially active
When the compressive strain amount of the elastic layer is as large as 2% or more, for example,
When growing thicker than the critical film thickness,
Even if non-equilibrium growth is performed, growth cannot be performed due to the presence of defects.
This is particularly problematic. The presence of strained layers crawls such defects
The reduction of slag is effective for improving luminous efficiency and
Can grow a layer having a compressive strain of, for example, 2% or more.
Can be grown thicker than the critical film thickness.
This Ga_xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0
<Y ≦ 1) layer is in contact with the active region and carries
It also has the role of confining_xIn_1-x
P_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1)
The smaller the number, the larger the bandgap energy
I can take it. For example, Ga_xIn_1-xP (when y = 1)
In the case of x, the lattice constant increases as x increases and approaches GaP.
And the band gap increases. Band guy
In the direct transition, Eg (＝) = 1.351 + 0.6
43x + 0.786x², Eg (X) = 2.
24 + 0.02x. So the active area
Ga_xIn_1-xP_yAs _1-y(0 <x ≦ 1, 0 <y
≦ 1) Carrier confinement because the hetero barrier of the layer becomes large
Better, lower threshold current, improve temperature characteristics, etc.
Has the effect of Furthermore, this Ga_xIn_1-xP_yAs
_1-y(0 <x ≦ 1, 0 <y ≦ 1)
The coupling prevention layer has a lattice constant larger than that of the GaAs substrate.
And has a compressive strain, and the lattice constant of the active layer is
The Ga_xIn_1-xP_yAs_{1 -Y}(0 <x ≦ 1, 0
<Y ≦ 1) It has a larger compressive strain than the layer. Again
Ga_xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <
y ≦ 1) Since the strain direction of the layer is the same as that of the active layer,
It works to reduce the substantial amount of compressive strain felt by the layer. distorted
The active layer is more sensitive to external factors as
Is large, for example, 2% or more, or the critical film thickness
It is particularly effective when the value exceeds.

For example, a surface emitting type having an oscillation wavelength of 1.3 μm band
The laser is preferably formed on a GaAs substrate.
In many cases, a semiconductor multilayer reflector is used for the reflector.
The active layer is a semiconductor layer having a thickness of 5 to 8 μm and 50 to 80 layers.
It must be grown before growth (while edge-emitting lasers
In this case, the total thickness before growing the active layer is about 2 μm and 3
It is only necessary to grow about a semiconductor layer). in this case,
Even if a high quality GaAs substrate is used, various causes (once
Generated defects basically creep up in the crystal growth direction
And GaAs based defects)
Defects on the surface just before active layer growth compared to the defect density on the plate surface
Density will inevitably increase. Before growing the active layer, strain
Insertion of a layer and the amount of substantial compressive strain felt by the active layer are reduced.
Reduces the effect of defects on the surface just before the active layer growth.
I will be able to. In this example, in the active area and with the reflector
Since the structure does not contain Al at the interface with the active region,
Crystal defects caused by Al during carrier injection
Non-radiative recombination disappeared, and non-radiative recombination was reduced.
As described above, Al is contained at the interface between the reflector and the active region.
Structure, that is, a non-radiative recombination prevention layer is provided.
It is preferable to apply this to both upper and lower reflectors,
It is effective to apply it to only one of the reflectors. Also this
In the example, both the upper and lower reflectors are semiconductor distributed Bragg reflectors.
However, one of the reflectors is a semiconductor distributed Bragg reflector,
The other reflecting mirror may be a dielectric reflecting mirror. Also mentioned above
In the example, only the layer closest to the active layer of the mirror low refractive index layer is
Ga_xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y
≦ 1), but a plurality of layers of G
a _xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦
1) may be a non-radiative recombination preventing layer. Further examples
Then, the lower reflector between the GaAs substrate and the active layer
Applying the idea, starting with Al, which is a problem when growing the active layer
Of crystal defects caused by creeping into active layer
The active layer can be crystallized with high quality.
You. As a result, luminous efficiency is high and reliability is practically sufficient.
A good surface emitting semiconductor laser was obtained. Also, semiconductor components
Not all, but all, of the low index layers of the cloth Bragg reflector
At least the portion closest to the active region is Ga containing no Al._x
In_1-xP_yAs _1-y(0 <x ≦ 1, 0 <y ≦ 1)
Increases the number of stacked mirrors, especially since it is only a layer
Without the above, the above-mentioned effect can be obtained. like this
The oscillation wavelength of the surface-emitting type semiconductor laser manufactured in
It was 1.2 μm. GaInAs on GaAs substrate
Increases the wavelength by increasing the In composition, but increases the amount of strain.
No limit is considered to be the limit for longer wavelengths up to 1.1 μm.
(Reference "IEEE Photonics.Technol.Lett.Vol.9
(1997) pp. 1319-1321 ").

However, as manufactured by the present inventors, a highly strained GaInAs quantum well active layer can be grown coherently thicker than before by a method of high non-equilibrium growth such as low temperature growth at 600 ° C. or lower. Could reach 1.2 μm. This wavelength is transparent to the Si semiconductor substrate. Therefore, light transmission through the Si substrate becomes possible in a circuit chip in which an electronic element and an optical element are integrated on the Si substrate. As is clear from the above description, it has been found that a long-wavelength surface emitting semiconductor laser can be formed on a GaAs substrate by using GaInAs having a high In composition and a high compression strain for the active layer. As described above, such a surface-emitting type semiconductor laser has a MOCV
Although the growth can be performed by the D method, other growth methods such as the MBE method can also be used. Although the triple quantum well structure (TQW) has been described as an example of the stacked structure of the active layer, a structure (SQW, MQW) using a quantum well of another number of wells may be used. The structure of the laser may be another structure. The length of the resonator was set to the thickness of λ, but λ / 2
Can be an integer multiple of. Desirably, it is an integral multiple of λ. Although the example using GaAs as the semiconductor substrate has been described, the above concept can be applied to a case where another semiconductor substrate such as InP is used. The period of the reflecting mirror may be another period. In this example, the main element is G for the active layer.
a, In, As layer, that is, Ga _x In _1-x
Although an example of As (GaInAs active layer) has been described, in order to perform laser oscillation of a longer wavelength, a layer (GaInNAs active layer) in which N is added and the main element is Ga, In, N, and As is used. Good. By actually changing the composition of the GaInNAs active layer, it was possible to perform laser oscillation in each of the 1.3 μm band and the 1.55 μm band. By examining the composition, a surface emitting laser having a longer wavelength, for example, in the 1.7 μm band can be obtained. Further, even if GaAsSb is used for the active layer, the active layer is formed on the GaAs substrate at 1.3.
A μm band surface emitting laser can be realized. Thus, the wavelength 1.
Conventionally, there is no suitable material for the semiconductor laser of 1 μm to 1.7 μm, but GaInAs and GaInN with high strain are used for the active layer.
By using As and GaAsSb and providing a non-radiative recombination preventing layer, a high-performance surface-emitting laser can be realized in a long wavelength region of 1.1 μm to 1.7 μm where stable oscillation has conventionally been difficult. Now you can.

Next, the present invention is applied to the optical transmitting / receiving system of the present invention.
Other long-wavelength surface-emitting semiconductor lasers
The configuration will be described with reference to FIG. Again, figure
N-GaAs substrate having a plane orientation of (100) as in the case of 1.
21 is used. Oscillation wave in each medium
N-Al with a thickness 1/4 times the length λ (thickness of λ / 4)_xG
a_1-xAs (x = 0.9) and n-Al_xGa_1-xA
n-semiconductor distribution in which s (x = 0) is alternately stacked for 35 periods
Bragg reflector 24 (Al _0.9Ga_0.1As / Ga
As lower reflector), and a λ / 4-thick n is formed thereon.
-Ga_xIn_1-xP_yAs_1-y(X = 0.5, y =
1) Layers were laminated. In this example, n-Ga_xIn_1-xP
_yAs_1-yThe (x = 0.5, y = 1) layer is also the lower reflector
It is a part and is a low refractive index layer. And on top of that,
Undoped lower GaAs spacer layer 23 and three Ga layers
_xIn_1-xN_yAs_1-yActive layer 3 which is a quantum well layer
3 (quantum well active layer) and GaAs barrier layer 34 (15n
m) of the multi-quantum well active layer (3 in this example)
Quantum well (TQW)) and undoped upper GaAs
An oscillation wavelength in the medium is formed by laminating the
A resonator having a thickness of one wavelength (thickness of λ) is formed.
You. In addition, a p-semiconductor distributed Bragg reflector
(Upper reflector) 24 is formed. The upper reflector is
The AlAs layer 27 serving as the selectively oxidized layer is formed as a GaInP layer.
Low refractive index layer having a thickness of 3λ / 4 sandwiched between AlGaAs layers
(C-doped p-Ga having a thickness of (λ / 4-15 nm)_xI
n_1-xP_yAs_1-y(X = 0.5, y = 1) layer, C
Doped p-Al_zGa_1-zAs (z = 1) selective oxidation
Layer (thickness 30 nm), thickness (2λ / 4-15 nm)
C-doped p-Al_xGa_1-xAs layer (x = 0.9)
GaAs layer (one period) having a thickness of λ / 4, and C-doped
P-Al_xGa_{1 -X}As layer (x = 0.9) and pA
l_xGa_1-xAs (x = 0) layer in each medium
Period alternately stacked with a thickness of 1/4 of the oscillation wavelength
Structure (22 periods)
Reflector (Al_0.9Ga_0.1As / GaAs upper part
Reflecting mirror).

Also in this example, although the illustration is omitted because it becomes complicated in FIG. 10, the structure of the semiconductor distributed Bragg reflector has a low refractive index layer (low refractive index layer) as shown in FIG. Al _{z Ga} 1-z a the layers) and between the high refractive index layer (a layer having a refractive index is large), the refractive index takes a value between the small and large
A hetero spike buffer layer made of s (0 ≦ y <z <x ≦ 1) is provided. And, at the top, p-Al _x
The Ga _1-x As (x = 0) layer also has a role as a contact layer (p-contact layer) for making contact with an electrode. Here, the In composition x of the quantum well active layer
Was 37% and the N (nitrogen) composition was 0.5%. The thickness of the quantum well active layer was 7 nm. The surface emitting semiconductor laser was grown by MOCVD. Materials for forming each layer of the semiconductor laser include TMA (trimethylaluminum), TMG (trimethylgallium), TM
I (trimethylindium), AsH ₃ (arsine),
PH ₃ (phosphine), and DMH as raw material for nitrogen
y (dimethylhydrazine) was used. Since DMHy decomposes at low temperature, it is suitable for low-temperature growth at a temperature of 600 ° C. or lower, and is particularly preferable when growing a quantum well layer having a large strain that requires low-temperature growth. Note that H ₂ was used as a carrier gas.

In this example, the GaInNAs layer (quantum
The well active layer was grown at 540 ° C. MOCVD is too
Crystallization of materials with high saturation and containing N and other V-groups at the same time
Suitable for long. In addition, high vacuum like MBE method is required
Instead, it is sufficient to control the supply flow rate and supply time of the source gas
Therefore, it is also excellent in mass productivity. Further, in this example, the predetermined
The mesa portion of size is p-Ga_xIn_1-xP_yAs
_1-y(X = 0.5, y = 1) pA until reaching the layer
l_zGa_1-zAs (z = 1) Exposing the side surface of the selective oxidation layer
Al formed on the side surface_zGa_1-zAs
(Z = 1) layer is oxidized from the side with water vapor to form Al_xO_yElectric
A flow narrowing layer is formed. Finally polyimide (insulation
Fill the part removed by mesa etching with film) and flatten
To remove the polyimide on the upper reflector,
A p-side electrode is formed on the semiconductor layer except for the light emitting portion, and GaAs
An n-side electrode was formed on the back surface of the s substrate. In this example
Is formed as a part of the upper reflecting mirror below the layer to be selectively oxidized.
_xIn _1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦
1) Inserting layers. For example, for wet etching
In this case, if a sulfuric acid-based etchant is used, AlGaAs
GaInPAs system as an etch stop layer
Ga can be used_xIn_1-xP_yAs
_1-y(0 <x ≦ 1, 0 <y ≦ 1) layer is inserted
Stricter mesa etching height for selective oxidation
Can be controlled. For this reason, uniformity and reproducibility can be improved,
Cost reduction can be achieved. The surface-emitting type semiconductor laser of this example
When the (element) is integrated in one or two dimensions, the element
The better controllability during manufacturing allows the array
Very good uniformity and reproducibility of element characteristics of each element
It has the effect of becoming.

In this example, the etching stop layer is
Ga that doubles_xIn_1-xP_yAs_{1 -Y}(0 <x ≦ 1,
0 <y ≦ 1) layer is provided on the upper reflecting mirror side, but the lower reflecting mirror
It may be provided on the side. Also in this example, the upper and lower reflectors
Between active regions where carriers are injected and recombined
(In this embodiment, the upper and lower spacer layers and the multiple quantum well
In the resonator comprising the active layer, A
l and no lower and upper reflectors
The layer closest to the active layer of the low refractive index layer is Ga_xIn_1-xP
_yAs _1-yNon-radiative reconnection of (0 <x ≦ 1, 0 <y ≦ 1)
It is a matching prevention layer. In other words, in this example,
And a structure that does not contain Al at the interface between the reflector and the active region.
Was caused by Al at the time of carrier injection.
To reduce non-radiative recombination caused by crystal defects
it can. Note that Al is not contained at the interface between the reflector and the active region.
Can be applied to the upper and lower reflectors as in this example.
Preferred, but can be applied to just one of the mirrors
effective. In this example, both the upper and lower reflectors are semiconductor components.
A cloth Bragg reflector was used, but one of the reflectors was a semiconductor distribution
A Bragg reflector and the other mirror as a dielectric mirror
May be. Also in this example, the GaAs substrate and the active layer
The same idea as in the example of Fig. 1 is applied to the lower reflector during
Caused by Al which is a problem during the growth of the active layer.
Negative effects due to crawling of crystal defects into active layer are suppressed
Thus, the active layer can be grown with high quality crystal. What
In addition, such a non-radiative recombination preventing layer is provided in FIG. 1 and FIG.
In either configuration, a semiconductor distributed Bragg reflector
The thickness of the oscillating wave in the medium.
The thickness is set to １ ／ of the length λ (thickness of λ / 4). Ah
Alternatively, a plurality of layers may be provided.

Although an example in which the non-radiative recombination preventing layer is provided on a part of the semiconductor Bragg reflector has been described above, the non-radiative recombination preventing layer may be provided in the resonator. For example,
The resonator section is composed of an active layer composed of a GaInNAs quantum well layer and a GaAs barrier layer, and GaAs is a first barrier layer.
A structure in which a non-radiative recombination preventing layer made of nPAs, GaAsP, and GaInP is used as the second barrier layer is exemplified. The thickness of the resonator section can be one wavelength. Since the band gap of the non-radiative recombination prevention layer is larger than that of the GaAs first barrier layer, the active region into which carriers are injected substantially extends to the GaAs barrier layer. Also, the remaining Al raw material,
In the case where a step of removing an Al reactant, an Al compound, or Al is provided, the step may be provided in the middle of the non-radiative recombination preventing layer, or a GaAs layer may be provided between the non-radiative recombination preventing layer and the layer containing Al. And can be performed in the middle of the layer. As is clear from the above description, a surface-emitting type semiconductor laser having high luminous efficiency and sufficient reliability for practical use was obtained with such a configuration. Also, not all of the low refractive index layers of the semiconductor distributed Bragg reflector, but at least the portion closest to the active region is Ga _x In containing no Al.
_{1-x Py} As _1-y (0 <x ≦ 1, 0 <y ≦ 1) is used as the non-radiative recombination preventing layer, so that the above-described effect can be obtained without particularly increasing the number of stacked reflectors. I was able to.

In addition, even with such a configuration, since the polyimide can be easily embedded, the wiring (p-side electrode in this example) is hardly disconnected, and a device having high reliability can be obtained. The oscillation wavelength of the surface emitting semiconductor laser manufactured in this manner was about 1.3 μm. In this example, a layer composed mainly of Ga, In, N, and As was used as the active layer (GaInNAs active layer), so that a long-wavelength surface emitting semiconductor laser could be formed on a GaAs substrate. Also, the current was narrowed by selective oxidation of the selectively oxidized layer mainly composed of Al and As, so that the threshold current was low. According to the current narrowing structure using the current narrowing layer made of the Al oxide film in which the selective oxidation layer is selectively oxidized, the current spreading can be suppressed by forming the current narrowing layer close to the active layer,
Carriers can be efficiently confined in a minute region that does not come into contact with the atmosphere. Further, by oxidizing to form an Al oxide film, the refractive index is reduced, light can be efficiently confined in a minute region in which carriers are confined by the effect of a convex lens, the efficiency is extremely improved, and the threshold current can be reduced. . In addition, because the current narrowing structure can be easily formed,
Manufacturing costs can be reduced. As is clear from the above description, even in the configuration as shown in FIG. 10, as in the case of FIG.
A surface emitting semiconductor laser in the 1.3 μm band can be realized, and a low-power and low-cost device can be obtained.

Although the surface emitting semiconductor laser shown in FIG. 10 can be grown by MOCVD as in the case of FIG. 1, other growth methods such as MBE can be used. Although DMHy is used as a nitrogen source, activated nitrogen and other nitrogen compounds such as NH ₃ may be used. Furthermore, although an example of a triple quantum well structure (TQW) has been shown as the stacked structure of the active layer, a structure (SQW, DQW, MQW) using a quantum well of another number of wells may be used. The structure of the laser may be another structure.
In the surface-emitting type semiconductor laser shown in FIG.
By changing the composition of the NAs active layer, the 1.55 μm band,
Further, a longer-wavelength surface-emitting type semiconductor laser in the 1.7 μm band can be used. Tl, S in GaInNAs active layer
Other III-V elements such as b and P may be contained. Even if GaAsSb is used for the active layer, GaAs
A 1.3 μm band surface emitting semiconductor laser can be realized on a substrate. In the present invention, the main element for the active layer is G
Although a description has been given of using a layer made of a, In, and As (GaInAs active layer) or a layer made of Ga, In, N, and As and adding N as a main element (GaInNAs active layer), other than GaNAs, GaPN , GaNPAs, G
aInNP, GaNAsSb, GaInNAsSb and the like can also be suitably used. Particularly in the case of an active layer containing nitrogen as in these examples, the non-radiative recombination preventing layer of the present invention is particularly effective. This will be described below.

FIG. 11 shows a room-temperature photoluminescence spectrum of an active layer having a GaInNAs / GaAs double quantum well structure including a GaInNAs quantum well layer and a GaAs barrier layer manufactured by our MOCVD apparatus. FIG. 12 shows a sample structure. 20 on GaAs substrate
1, a lower cladding layer 202, an intermediate layer 203, an active layer 204 containing nitrogen, an intermediate layer 203, and an upper cladding layer 205.
Are sequentially laminated. In FIG. 11, A is AlGa
A sample in which a double quantum well structure is formed on an As clad layer with a GaAs intermediate layer interposed therebetween, and a sample B in which a double quantum well structure is continuously formed with a GaAs intermediate layer interposed on a GaInP clad layer. It is. As shown in FIG. 11, the photoluminescence intensity of Sample A is lower than that of Sample B by less than half. Therefore, when an active layer containing nitrogen such as GaInNAs is continuously formed on a semiconductor layer containing Al as a constituent element such as AlGaAs using one MOCVD apparatus, the emission intensity of the active layer is deteriorated. A problem arose. Therefore, the threshold current density of the GaInNAs-based laser formed on the AlGaAs cladding layer is 2 times smaller than that formed on the GaInP cladding layer.
More than twice as high.

The elucidation of the cause was examined. FIG. 13 shows the nitrogen and oxygen concentrations when an element having a cladding layer of AlGaAs, an intermediate layer of GaAs, and an active layer of a GaInNAs / GaAs double quantum well structure was formed using a single epitaxial growth apparatus (MOCVD). FIG. 5 is a diagram showing a distribution in a depth direction. The measurement was performed by SIMS. Table 1 shows the measurement conditions.

[Table 1] In FIG. 13, two nitrogen peaks are observed in the active layer corresponding to the GaInNAs / GaAs double quantum well structure. Then, an oxygen peak is detected in the active layer. However, the oxygen concentration in the intermediate layer containing neither N nor Al is about one digit lower than the oxygen concentration in the active layer. On the other hand, the cladding layer is made of GaInP, the intermediate layer is made of GaAs, and the active layer is made of GaInNAs / GaAs2.
When the distribution of the oxygen concentration in the depth direction was measured for the element configured as the quantum well structure, the oxygen concentration in the active layer was at the background level. That is, when a semiconductor light emitting device having a semiconductor layer containing Al between a substrate and an active layer containing nitrogen is continuously grown by a single epitaxial growth apparatus using a nitrogen compound raw material and an organic metal Al raw material, Our experiments revealed that oxygen was incorporated into the active layer containing nitrogen. Oxygen incorporated in the active layer forms a non-radiative recombination level,
The luminous efficiency of the active layer is reduced. Oxygen incorporated in this active layer causes A between the substrate and the active layer containing nitrogen.
It has been newly found that this is a cause of lowering the luminous efficiency of a semiconductor light emitting element provided with a semiconductor layer containing l. The origin of this oxygen is considered to be a substance containing oxygen remaining in the apparatus or a substance containing oxygen contained as an impurity in the nitrogen compound raw material.

Next, the cause of oxygen uptake was examined. FIG. 14 is a diagram illustrating the distribution of Al concentration in the depth direction of the same sample as in FIG. 13. The measurement was performed by SIMS. Table 2 shows the measurement conditions.

[Table 2] FIG. 14 shows that Al was detected in the active layer into which the Al material was not originally introduced. However, in the intermediate layer (GaAs layer) adjacent to the semiconductor layer containing Al (cladding layer), the Al concentration is about one digit lower than that of the active layer. This indicates that Al in the active layer is not diffused, replaced or mixed in from the semiconductor layer (cladding layer) containing Al. On the other hand, like GaInP, Al
When an active layer containing nitrogen was grown on a semiconductor layer containing no, Al was not detected in the active layer. Therefore,
The Al detected in the active layer is the Al source remaining in the growth chamber or in the gas supply line, or an Al reactant, or an Al compound, or Al reacts with the nitrogen compound source or impurities (such as moisture) in the nitrogen compound source. It is bonded and taken into the active layer. That is, when a semiconductor light emitting device having a semiconductor layer containing Al between a substrate and an active layer containing nitrogen is continuously crystal-grown by a single epitaxial growth apparatus using a nitrogen compound raw material and an organic metal Al raw material. It was newly found that Al was naturally taken into the active layer containing nitrogen.

As compared with the nitrogen and oxygen concentration distributions in the depth direction in the same device shown in FIG. 14, the two oxygen peak profiles in the double quantum well active layer do not correspond to the nitrogen concentration peak profiles. 14 corresponds to the Al concentration profile of FIG. From this, GaIn
Oxygen impurities in the NAs well layer are more likely to be introduced into the well layer than to be taken in with the nitrogen source.
It was clarified that they were incorporated together with l. That is, the Al raw material remaining in the growth chamber or Al
When the reactant, or Al compound, or Al comes into contact with the nitrogen compound raw material, Al is combined with a substance containing oxygen such as water contained in the nitrogen compound raw material or water remaining in the gas line or the reaction chamber. Then, Al and oxygen are taken into the active layer. Our experiments have clarified for the first time that oxygen taken into the active layer has reduced the luminous efficiency of the active layer. So to improve this,
At least the Al source material, the Al reactant, or the Al compound, or the Al remaining in the growth chamber in a place where the nitrogen compound source material or the impurities contained in the nitrogen compound source material touch.
It has been found that it is necessary to provide a step of removing. If this step is provided after the growth of the semiconductor layer containing Al and before the start of the growth of the active layer containing nitrogen, when the nitrogen compound raw material is supplied to the growth chamber to grow the active layer containing nitrogen, the remaining Al Raw material, or Al reactant, or A
l compound or Al reacts with a nitrogen compound raw material or an impurity contained in the nitrogen compound raw material and a substance containing oxygen remaining in the device, and Al taken into the active layer.
And the concentration of oxygen impurities could be reduced. Furthermore,
If removed before the end of the non-radiative recombination prevention layer growth,
When carriers are injected into the active layer by current injection, it is preferable because adverse effects on non-radiative recombination in the active layer can be suppressed. For example, the Al concentration in the active layer containing nitrogen is 1 × 1
By reducing it to 0 ¹⁹ cm ⁻³ or less, continuous oscillation at room temperature became possible. Further, Al in the active layer containing nitrogen
By reducing the concentration to 2 × 10 ¹⁸ cm ⁻³ or less, light emission characteristics equivalent to those formed on a semiconductor layer containing no Al were obtained. An Al source, an Al reactant, or an Al compound remaining in a place where a nitrogen compound source or an impurity contained in the nitrogen compound source touches in the growth chamber;
Alternatively, the step of removing Al includes, for example, providing a step of purging with a carrier gas. Here, during the time of the purge step, after the growth of the Al-containing semiconductor layer ends and the supply of the Al raw material to the growth chamber is stopped, the nitrogen compound raw material is used to start the growth of the nitrogen-containing semiconductor layer. This is the interval until the material is supplied to the growth chamber. As a method of the purging, there is a method of interrupting the growth in an intermediate layer containing neither Al nor nitrogen and purging with a carrier gas. When the growth is interrupted and purged, the place where the growth is interrupted is set to Al
Can be provided from after the growth of the semiconductor layer containing the compound to the middle of the non-radiative recombination preventing layer.

FIG. 15 shows an example of a sectional structural view of a semiconductor light emitting device for explaining that a step of purging with a carrier gas in the present invention is provided. 15, a first semiconductor layer 202 containing Al as a constituent element, a first lower intermediate layer 601, a second lower intermediate layer 602, an active layer 204 containing nitrogen, and an upper intermediate layer 20 are formed on a substrate 201.
Third, the second semiconductor layer 205 is sequentially stacked. For crystal growth, an epitaxial growth apparatus using an organic metal Al raw material and an organic nitrogen raw material is used. A growth interruption step is provided between after the growth of the first lower intermediate layer and the start of the growth of the second lower intermediate layer. During the growth interruption, the Al source material, the Al reactant, or the Al compound, or the Al remaining in the growth chamber where the nitrogen compound source material or the impurities contained in the nitrogen compound source material touch is purged with hydrogen as a carrier gas. Has been removed. FIG.
6 is a first lower intermediate layer 601 and a second lower intermediate layer 60
2 shows a measurement result of the distribution of the Al concentration in the depth direction in a semiconductor light emitting device in which the growth was interrupted between 2 and the purge time was set to 60 minutes. As shown in FIG. 16, the Al concentration in the active layer is 3 ×
It could be reduced to 10 ¹⁷ cm ⁻³ or less. This value is about the same as the Al concentration in the intermediate layer. FIG.
FIG. 7 shows the result of measuring the distribution of the nitrogen and oxygen concentrations in the depth direction for the same device. As shown in FIG. 17, the oxygen concentration in the active layer was reduced to a background level of 1 × 10 ¹⁷ cm ⁻³ .

The reason why a peak appears in the oxygen concentration in the lower intermediate layer is that oxygen segregates at the growth interruption interface. Therefore, in the case of purging after interrupting the growth, it is preferable that the place where the growth is interrupted be provided after the growth of the Al-containing semiconductor layer until the end of the growth of the non-radiative recombination preventing layer. The non-radiative recombination prevention layer can increase the bandgap energy compared to the quantum well active layer and the barrier layer. This is because adverse effects due to the above can be suppressed. When an active layer containing nitrogen is used as described above, providing a non-radiative recombination preventing layer is particularly effective. In this semiconductor light emitting device, the growth is interrupted between the first lower intermediate layer and the second lower intermediate layer, and the purge time is set to 60 minutes to reduce the concentration of impurities such as Al and O in the active layer containing nitrogen. Could be reduced. Thereby, the luminous efficiency of the active layer containing nitrogen could be improved. In the step of purging the growth chamber with a carrier gas, by purging the susceptor while heating it, the Al raw material and reaction products adsorbed on the susceptor or around the susceptor can be degassed and removed efficiently. However, when the substrates are heated simultaneously, it is necessary to keep supplying a group V source gas such as AsH ₃ or PH ₃ to the growth chamber even during the interruption of the growth, in order to prevent the semiconductor layer on the outermost surface from being thermally decomposed. is there. Further, when purging the growth chamber with a carrier gas, the substrate can be transferred from the growth chamber to another chamber. By transporting the substrate from the growth chamber to another chamber, there is no need to supply a group V source gas such as AsH ₃ or PH ₃ to the growth chamber when purging while heating the susceptor. Therefore, the thermal decomposition of the reaction product containing Al deposited around the susceptor or the susceptor can be further promoted. Thereby, the Al concentration in the growth chamber can be efficiently reduced.

Further, there is a method of performing purging while growing the intermediate layer. Since the non-radiative recombination preventing layer is provided between the AlGaAs-based reflecting mirror containing Al and the nitrogen-containing active layer, the distance between the Al-containing layer and the nitrogen-containing active layer becomes longer. Therefore, there is an advantage that the purge time can be lengthened even when the purge is performed while growing. In this case, it is better to slow down the growth rate and lengthen the time. There is also a method in which a reflecting mirror made of AlGaAs containing Al and an active layer containing nitrogen are formed by different apparatuses. Even in this case, if the regrowth interface is provided below the non-radiative recombination preventing layer, the concentration of impurities such as Al and O in the active layer containing nitrogen can be reduced. As in the case of the ordinary MBE method, when the crystal is formed by a crystal growth method that does not use the organometallic Al raw material and the nitrogen compound raw material, the Al is placed between the substrate and the active layer containing nitrogen.
No report has been made on a decrease in luminous efficiency in a semiconductor light emitting device provided with a semiconductor layer containing. On the other hand, MOCVD
In the method, GaInNA formed on a semiconductor layer containing Al is used.
It has been reported that the luminous efficiency of the s active layer is reduced. Electro
n. Lett., 2000, 36 (21), pp 1776-1777, GaAs is deposited on an AlGaAs cladding layer in the same MOCVD growth chamber.
s even if an intermediate layer made of GaIn is provided.
It has been reported that growing a NAs quantum well layer significantly reduces the photoluminescence intensity. In the above report, an AlGaAs cladding layer and a GaInNAs active layer are grown in different MOCVD growth chambers in order to improve the photoluminescence intensity. Therefore, M
In the case of a crystal growth method using an organic metal Al raw material and a nitrogen compound raw material, such as the OCVD method, this is a problem that occurs at least. In the MBE method, crystal growth is performed under ultra-low pressure (in a high vacuum), whereas in the MOCVD method, several tens Torr are usually used.
Since the pressure of the reaction chamber is higher than that of the MBE method from r to about atmospheric pressure, the mean free path is overwhelmingly short, and the supplied raw material or carrier gas comes into contact with others in a gas line, a reaction chamber, or the like.
It is thought to react. Therefore, in the case of a growth method in which the pressure in the reaction chamber or gas line is high, such as the MOCVD method, it is more preferable to prevent non-radiative recombination after the growth of the semiconductor layer containing Al and before the growth of the active layer containing nitrogen. A step is provided for removing the Al source material, the Al reactant, or the Al compound, or the Al remaining at the place where the nitrogen compound source or the impurities contained in the nitrogen compound source touches in the growth chamber until after the layer growth is completed. This has a high effect of preventing oxygen from being taken into the active layer containing nitrogen. For example, there is a method in which a gas line or a growth chamber is evacuated after growing a semiconductor layer containing Al and before growing an active layer containing nitrogen. In this case, the effect is high if heating is performed.

There is also a method of removing the semiconductor layer containing Al by flowing an etching gas after growing the semiconductor layer before growing the active layer containing nitrogen. An example of a gas that can react with and remove an Al-based residue is an organic-based compound gas. As described above, when a DMHy gas, which is one of the organic compound gases, is supplied using a DMHy cylinder during the growth of the active layer containing nitrogen, it is apparent that the gas reacts with the Al-based residue. Therefore, after growing a semiconductor layer containing Al,
When organic compound gas is supplied using an organic compound gas cylinder before the growth of the active layer containing nitrogen, Al-based residue remaining on the reaction chamber side wall, the heating zone, the jig holding the substrate, and the like. Can be removed by reacting with oxygen, so that the incorporation of oxygen into the active layer can be suppressed. Furthermore, it is preferable to use the same gas as the nitrogen material of the active layer containing nitrogen, since it is not necessary to add a special gas line. This step may be performed with the growth interrupted.
A layer containing nitrogen, such as an NAs or GaInNP layer, may be formed by crystal growth as a dummy layer separately from the active layer. It is preferable to perform the Al removal step by crystal growth as compared with the case where the growth is interrupted, because there is no time loss. Note that Ga is used for the active layer.
In the case of using InAs, it has conventionally been considered that the wavelength limit is 1.1 μm or less, but it is possible to grow a GaInAs quantum well active layer having a high strain with a high strain by growing at a low temperature of 600 ° C. or less. , The wavelength can reach up to 1.2 μm. As described above, a semiconductor laser having a wavelength of 1.1 μm to 1.7 μm does not have a material suitable for a conventional semiconductor laser. Wavelength of 1.1 μm to 1.7 μm, which has conventionally been difficult to achieve stable oscillation
In the long wavelength region of the band, a high-performance surface emitting laser can be realized, and application to an optical communication system has become possible. FIG. 18 shows an example in which such a long wavelength band surface emitting semiconductor laser device is formed as a large number of chips on an n-GaAs wafer 40 having a plane orientation of (100), and a laser device chip. In the laser element chip shown here, 1 to n laser elements 41 are formed, and the number n and the arrangement method are determined according to the application.

Next, the present invention will be described below with respect to a coupling portion between a semiconductor laser and an optical fiber or an optical waveguide.
First, as shown in FIG. 19, a laser beam emitted from a semiconductor laser 52 in a direction normal to a substrate has an intensity distribution close to a Gaussian function on a detection surface perpendicular to its optical axis. was gotten. Here, the beam diameter is defined as the full width at half maximum (FWHM) of the profile, and the beam diameter 5
0 and the distance 51 between the semiconductor laser and the detection surface, the light emission angle θ
Can be measured. In the surface emitting semiconductor laser of this example, a value of about 5 to 10 degrees was obtained isotropically. on the other hand,
It is known that conventionally known edge emitting semiconductor lasers in the 1.1 to 1.7 μm band have a large light emission angle and anisotropy. As typical values, the light emission angle _{θθ in the} direction perpendicular to the substrate of the semiconductor laser is 〜35 degrees, and the light emission angle θ _{// in the} direction parallel to the substrate is 25 degrees. Therefore,
In a conventional edge emitting semiconductor laser, a microlens or the like has been used in an optical fiber or an optical waveguide to obtain efficient optical coupling. On the other hand, in the semiconductor laser of this embodiment, since the light emission angle is small as described above, such a microlens is unnecessary, and there is a possibility that the semiconductor laser can be brought close to the optical fiber or the optical waveguide. In addition, since the light emission angle is small, even if there is a distance between the semiconductor laser and the optical fiber or the optical waveguide, the beam diameter is small, and a certain range is set in the optical path length between the semiconductor laser and the optical fiber or the optical waveguide. There is a possibility that good optical coupling can be obtained without using a lens. FIG. 20 is a schematic diagram showing the spread of the light of the semiconductor laser and the positional relationship between the optical fiber and the optical waveguide, and FIG. 21 shows an example of the calculation result of the spread of the beam diameter. The opening diameter of the semiconductor laser 53 is d [μ
m], the radiation angle is θ [degrees], the optical path length at the semiconductor laser-optical fiber end or the optical waveguide end is l [μm], and the core diameter of the fiber is X [μm]. Optical axis 54 of semiconductor laser 53
And the optical axis of the optical fiber or optical waveguide are coincident,
In the figure, these are indicated by wavy lines. Here, as for the opening diameter d, when the opening is a circle, if the diameter is a square, the length of one side of the square is d. In the case where the opening has a rectangular shape or another shape, the diameter of a circle having an area corresponding to the area of an ellipse inscribed therein is defined as d.

Here, the optical path length at the semiconductor laser-optical fiber end or the optical waveguide end is set in consideration of the case where light is turned back by the mirror 62 as shown in FIG. When the optical path is straight without such folding of light, the optical path length at the semiconductor laser-optical fiber end or the optical waveguide end is simply the distance between the semiconductor laser-optical fiber end or the optical waveguide end. In the case of the optical waveguide 63, the core 64
Is not a circle, but generally a rectangle or square,
In the case of a square, one side is X [μm], and in the case of a rectangle, the short axis is X [μm]. At this time, the beam emitted vertically from the semiconductor laser spreads as the optical path length l increases with the light emission angle θ, and reaches the end face of the optical fiber or the optical waveguide. The laser beam diameter at the end surface of the optical fiber or the waveguide is represented by d + 2 tan (θ / 2). It is considered that optical coupling is obtained. FIG. 21 shows, based on this formula, a case where the opening diameter of the semiconductor laser is 5 μm and the light emission angle is 10 degrees as an example of the present embodiment, and a case of an edge emission type with a light emission angle of 35 degrees as a comparative example. , Semiconductor laser
The relationship between the optical path length l at the end of the optical fiber or the end of the optical waveguide and the beam diameter is shown. In the case of this embodiment, the beam spread is smaller than that of the comparative example. The core diameter of a general multimode fiber as an optical fiber is 50 μm (cladding diameter 125 μm).
In the case of m), when 1 is 260 μm, the core diameter matches the beam diameter. If the core diameter and the beam diameter are within the distance between the semiconductor laser and the fiber end, the beam diameter is smaller than the fiber core diameter, and good coupling can be obtained without laser beam loss. . In other words,
It can be seen that the distance (alignment in the optical axis direction) between the semiconductor laser and the end of the optical fiber is very rough compared to the comparative example. GI-POF such as Cytop (Asahi Glass)
For example, when the core diameter is 100 μm, the laser beam diameter matches the core diameter, and the distance between the semiconductor laser and the end of the fiber is 550 μm. Can be.

FIG. 22 shows an example of a coupling section between a semiconductor laser and an optical fiber in a communication system using the above-mentioned surface emitting semiconductor laser. The communication system includes a surface-emitting type semiconductor laser 55, an optical transmission unit having a driving circuit therefor, a surface-type photodetector and a light receiving unit having the driving circuit, and an optical fiber or an optical waveguide acting as a transmission path therebetween. ing. Here, the drive circuits for the semiconductor laser and the photodetector are mounted on the same mounting board as the respective elements (not shown). In addition, by providing an optical transmitting unit and an optical receiving unit on both sides of the optical transmission path, bidirectional communication may be performed. A laser array element 57 in which surface emitting semiconductor lasers 55 having the structure shown in FIG. 1 are arranged in an array is mounted on a Si substrate having good thermal conductivity as a mounting substrate 56. The oscillation wavelength used was 1.3 μm. Here, the opening diameter of the semiconductor laser is set to 1
0 μm and 12 semiconductor lasers. The pitch of the semiconductor laser was 200 μm. Next, a hole array 58 made of aluminum nitride AlN and having a through hole of 125 μm corresponding to the diameter of the multimode fiber and having the same 200 μm pitch as the semiconductor laser was inserted into the laser array element 5.
7 and the guide 60 of the hole array element 58 were fixed so as to coincide with each other. At this time, the hole array 58 is in contact with the laser array element 57, has a very high thermal conductivity of about 300 Wm ⁻¹ K ^−1, and also functions as a heat radiating part. Therefore, heat generated by the oscillation of the semiconductor laser can be radiated also from the light emitting surface side, so that a more stable optical communication system can be obtained. Here, the multimode fiber 61 whose end face was polished was applied and fixed with an adhesive.
By doing so, accurate alignment can be obtained in the direction perpendicular to the optical axis. On the other hand, since only the optical fiber is applied in the direction perpendicular to the optical axis, rough alignment results in a space of about 0 to 20 μm between the semiconductor laser and the optical fiber. However, the light emission angle θ is 8 degrees and the aperture diameter d
Is 10 μm, even when the distance between the semiconductor laser and the optical fiber is 50 μm, the beam diameter is 17 μm, which is sufficiently smaller than the core diameter of the multi-fiber 61 of 50 μm, and satisfies the above expression, and good optical coupling is achieved. Obtained. Therefore, since a 1.3 μm surface-emitting type semiconductor laser is used and a lens is not used at the joint between the semiconductor laser and the optical fiber, the number of parts is small, the cost is low, and light whose alignment is gentle in the optical axis direction is low. The communication system could be built.

On the other hand, after the optical fiber was applied to the semiconductor laser, the amount of drawing was changed using a micrometer.
When the distance between the semiconductor laser and the optical fiber was 400 μm, the beam diameter was 66 μm, which was larger than the core diameter of the multi-fiber of 50 μm. When the above expression was not satisfied, sufficient optical coupling was not obtained. The experimental results are shown below. d + 2ltan (θ / 2) (μm) X (μm) Evaluation 1050 ○ 2050 ○ 30 50 ○ 40 50 ○ 50 50 ○ 60 50 △ 70 50 × 80 50 × 10 62.5 ○ 20 62.5 ○ 3062 .5 6 40 62.5 50 62.5 60 62.5 70 62.5 × 80 62.5 × Evaluation: Good optical coupling efficiency and endurable for practical use △ Optical coupling efficiency is slightly poor × The optical coupling efficiency is poor and the practical use is impossible. From the above results, the core diameter of the optical fiber is X, the aperture diameter of the semiconductor laser is d, the light emission angle of the semiconductor laser is θ, and the semiconductor laser is When the optical path length from the optical fiber to the optical fiber is l, X
It can be understood that is not practical unless the value is not less than d + 2 tan (θ / 2). In this case, the number of optical fibers is 12. However, the number may be one or may be 4, 8, 16, or any other appropriate number depending on data to be transmitted. A multi-mode fiber is used as the optical fiber. A single-mode fiber is suitable for transmitting large-capacity information over a long distance, and a plastic optical fiber (POF) is suitable for a short distance and low cost. However, the above equation holds for any optical fiber. The fiber end face may be subjected to a treatment such as a non-reflection coating. Although aluminum nitride AlN is used as the heat radiating portion, any material having a high thermal conductivity, such as ceramics such as Si, carbon, and alumina, can function as a heat radiating portion.

Next, another embodiment of the present invention will be described in the same manner as described above, with respect to a coupling portion between a semiconductor laser and an optical fiber. The configuration is almost the same as that shown in FIG. 22, except that the semiconductor laser and the optical fiber are in contact with each other, and the distance between the semiconductor laser and the optical fiber or the waveguide is substantially zero. Note that “contact” here is synonymous with “the distance between the semiconductor laser and the optical fiber or the waveguide is substantially zero”.
Taking into account the accuracy of the assembly, actually 0-1
The term "contact" includes up to 0 μm. A Si substrate having good heat conductivity is used as a mounting substrate, and a laser array element in which surface emitting semiconductor lasers having the structure shown in FIG. 1 are arranged in an array is mounted thereon. In this case, the one having an oscillation wavelength of 1.3 μm was used. Here, the opening diameter of the semiconductor laser is 10 μm, and the number of the semiconductor lasers is 12. The pitch of the semiconductor laser was 200 μm. Then, the multi-mode optical fiber is inserted into a hole array made of aluminum nitride AlN at the same 200 μm pitch as that of the semiconductor laser and having a through-hole of 125 μm corresponding to the multi-mode fiber diameter. Then, the optical fiber is slightly projected and fixed. Next, the optical fiber is polished, and the end of the optical fiber is made to coincide with the hole array surface on the side in close contact with the laser array element. After doing so, the marker is aligned with the guide as before, so that the optical axis of the surface emitting semiconductor laser and the optical fiber are aligned, and the laser array element and the hole array are fixed. The laser and the optical fiber can be brought into contact. In this case, higher light coupling efficiency was obtained than in the previous example. Since the beam is hardly spread and coincides with the aperture diameter, it is sufficiently smaller than the core diameter of the optical fiber, and the alignment margin perpendicular to the optical axis increases.
An optical communication system using a 3 μm surface emitting laser can be constructed.

In another embodiment of the present invention, a coupling portion between a semiconductor laser and an optical waveguide is shown in FIG.
Here, an example is shown in which a beam emitted from a semiconductor laser is folded by a mirror. A Si substrate having good heat conductivity is used as a mounting substrate, and a laser array element in which surface emitting semiconductor lasers having the structure shown in FIG. 1 are arranged in an array is mounted thereon. Here, the opening diameter of the semiconductor laser was 15 μm, and the number of semiconductor lasers was four. On the other hand, an optical waveguide is formed on a mounting substrate on which a mirror is mounted or formed monolithically. Here, the mirror is KO
A mirror on which anisotropic etching was performed by H and Ag was formed was mounted on a Si substrate. Further, an optical waveguide was formed on a mounting substrate having a mirror. After forming the cladding, the optical waveguide is formed of polymethyl methacrylate (PMM) in the core.
Using A), patterning was performed to form a cladding layer as an upper layer. The size was 50 × 50 μm. In addition to PMMA, a polymer waveguide such as polyimide, epoxy resin, polyurethane, or polyethylene, or an inorganic film such as a silicon oxide film can be used as the optical waveguide. Also,
As a forming method, a method of combining application and patterning such as spin coating or dip coating, or a method by resin molding or die processing is used. The mounting substrate having the laser array element and the substrate having the optical waveguide are fixed so that the optical axis of the semiconductor laser and the optical axis of the optical waveguide are aligned via a mirror. The light emission angle of the semiconductor laser is 10 degrees, the aperture diameter is 15 μm, and the optical path length l between the semiconductor laser and the waveguide is:
By changing the position of the end face of the optical waveguide, 50, 100,
Three types of 250 μm were prepared. Good optical coupling was obtained for optical path lengths of 50 and 100 μm that satisfied the above equation, but good optical coupling was not obtained for an optical path length of 250 μm that did not satisfy the above equation. However, compared with the conventional edge emitting semiconductor laser, no lens or the like is required, and the alignment in the optical axis direction is rough and good. Therefore, 1.2 μm
An optical communication system with gentle alignment in the optical axis direction was constructed using the surface emitting type semiconductor laser. Here, the mirror is formed separately from the waveguide, but the waveguide end face is processed to 45 degrees by a dicing blade or the like, and a metal such as Ag is formed on the inclined surface to integrate the waveguide and the mirror. It may be formed. The optical waveguide diameter is set to 50 μm for the multi-mode. However, in the case of the single mode, it is necessary to reduce the diameter to 10 μm, but basically the same expression holds. Here, the cross section of the optical waveguide is a square, but a plurality of optical signals may be transmitted by a single waveguide such as a rectangle or an optical sheet.

FIG. 24 shows another embodiment of the present invention, in which a semiconductor laser and an optical waveguide are connected in the same manner as described above.
A surface emitting semiconductor laser having the structure shown in FIG. 1 is mounted on a Si substrate having good thermal conductivity as a mounting substrate. Note that, also in this case, an oscillation wavelength of 1.3 μm was used. Here, the aperture diameter of the semiconductor laser is 7 μm, the light emission angle is 8 degrees, and the semiconductor laser is not an array but one.
And The mounting substrate on which the semiconductor laser was mounted was aligned with the package and fixed. Further, the optical axes of the semiconductor laser and the single mode optical fiber are made to coincide with each other by the optical fiber guide which is aligned with the package guide and the guide pin. The core diameter of the single mode optical fiber is 10 μm, the cladding diameter is 125 μm, and the diameter of the optical fiber guide matches the cladding diameter. Here, good optical coupling was obtained by bringing the single mode optical fiber into contact with the semiconductor laser. Since a single-mode optical fiber is used, long-range, high-bandwidth optical transmission becomes possible. An optical communication system having good optical coupling was constructed using a 1.3 μm surface emitting semiconductor laser.

[0047]

As described above, according to the first aspect of the present invention, by devising a semiconductor distributed Bragg reflector,
The operating voltage, the oscillation threshold current, and the like can be reduced, the laser element generates less heat, stable oscillation can be achieved, and a low-cost practical optical communication system can be realized. In addition, by using a surface-emitting type semiconductor laser capable of reducing operating voltage, oscillation threshold current, and the like, an optical communication system with low power consumption can be realized, and further, by setting the positional relationship between the semiconductor laser and an optical fiber or an optical waveguide. Since there is no need to use a lens, the number of components is small, alignment is loose in the optical axis direction, and good optical coupling efficiency with an optical fiber or an optical waveguide can be realized. According to the second aspect of the present invention, a surface-emitting type semiconductor laser device chip provided with a non-radiative recombination preventing layer enables stable oscillation and realizes a practical optical communication system using this as a light-emitting light source. . Also, by setting the positional relationship between the semiconductor laser and the optical fiber or the optical waveguide, it is not necessary to use a lens, so the number of parts is small,
The alignment was loose in the direction of the optical axis, and good optical coupling efficiency with the optical fiber or the optical waveguide was realized. According to claim 3, in such an optical communication system,
Since the semiconductor laser and the optical fiber or the optical waveguide are in contact with each other, the number of parts is small because a lens optical system is not required, and the alignment margin in the direction orthogonal to the optical axis is increased. Good optical coupling efficiency with the waveguide was realized. In claim 4, such an optical fiber or an optical waveguide has a heat radiating portion, and the heat radiating portion abuts on the semiconductor laser element chip, so that the heat generated by the semiconductor laser emission from the substrate side. In addition, since heat can be dissipated from the light emitting surface side, a more stable optical communication system can be realized. In claim 5, parallel signal processing can be performed by using a plurality of such optical fibers or optical waveguides and a surface emitting semiconductor laser device, so that a larger capacity optical communication system can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of an element part of a long-wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a configuration of a semiconductor distributed Bragg reflector of a long wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example in which the composition gradient of the hetero-spike buffer layer of the semiconductor distributed Bragg reflector applied to the present invention is larger near the GaAs layer than the AlAs layer.

FIG. 4 is a diagram showing an example in which the Al composition of the hetero-spike buffer layer is changed linearly.

FIG. 5 is a diagram showing a result of estimating a differential sheet resistance of the hetero-spike buffer layer of FIG. 3;

FIG. 6 is a band diagram showing a thermal equilibrium state of a DBR heterointerface of a semiconductor distributed Bragg reflector made of AlAs / GaAs.

FIG. 7 is a band diagram of the hetero-spike buffer layer of FIG. 3 in a thermal equilibrium state.

FIG. 8: AlAs / GaAs (p = 1E18 cm ⁻³ )
It is a figure which shows the resistivity of 4 pairs.

FIG. 9 is a graph showing the rate of change of the reflectance of an AlAs / GaAs semiconductor distributed Bragg reflector.

FIG. 10 is a sectional view of an element portion of another configuration of a long-wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 11 shows GaInNAs / according to an embodiment of the present invention.
FIG. 3 is a room-temperature photoluminescence spectrum diagram of an active layer having a GaAs double quantum well structure.

FIG. 12 is a structural diagram of a sample.

FIG. 13 is a diagram showing a depth direction distribution of nitrogen and oxygen concentrations.

FIG. 14 is a diagram showing the distribution of the Al concentration in the depth direction.

FIG. 15 is an explanatory structural view in the case where growth is interrupted by carrier gas purge.

FIG. 16 is a diagram showing the distribution of the Al concentration in the depth direction in a case where a growth interruption step is provided and purged with hydrogen.

FIG. 17 is a diagram showing a depth direction distribution of nitrogen and oxygen concentrations when a growth interruption step is provided and purged with hydrogen.

FIG. 18 is a plan view showing a wafer substrate and a laser element chip on which a long wavelength band surface emitting semiconductor laser element according to one embodiment of the present invention is formed.

FIG. 19 is a schematic diagram illustrating a relationship between a light emission angle and a beam diameter of a long wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 20 is a schematic diagram showing the relationship between the beam spread of the long wavelength band surface emitting semiconductor laser according to one embodiment of the present invention, the core diameter of the optical fiber, and the optical path length.

FIG. 21 is a diagram showing a calculation example showing the relationship between the beam diameter and the optical path length of the long wavelength band surface emitting semiconductor laser device according to one embodiment of the present invention.

FIG. 22 is a schematic diagram showing a coupling portion between a semiconductor laser and an optical fiber in an optical communication system using a long wavelength band surface emitting semiconductor laser device according to one embodiment of the present invention.

FIG. 23 is a schematic view showing a coupling portion between a semiconductor laser and an optical waveguide of an optical communication system using a long-wavelength band surface emitting semiconductor laser device according to an embodiment of the present invention.

FIG. 24 is a schematic diagram showing a coupling portion between a semiconductor laser and an optical waveguide of an optical communication system using a long-wavelength band surface emitting semiconductor laser device according to an embodiment of the present invention.

[Explanation of symbols]

1 n-side electrode, 2 n-GaAs substrate, 3 lower distributed Bragg reflector, 4 GaAs spacer layer, 5 upper distributed Bragg reflector, 6 p-contact layer,
12 TQW active layer, 13 GaAs barrier layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Teruyuki Furuta 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Kazuya Miyagaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Ken Kanai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Atsushi Watada 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Shunichi Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Satoru Sugahara 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Invention Person Shinji Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Shuichi Hikichi 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Inside Ricoh (72) Inventor Takuro Sekiya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Naoto Shakuya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company ( 72) Inventor Takashi Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 5F073 AA03 AA55 AA74 AB20 BA01 CA17 CB02 CB19 DA14 EA02

Claims (5)

[Claims] 1. A laser chip and a connection with the laser chip
In an optical communication system, the laser chip emits light.
Has an oscillation wavelength of 1.1 μm to 1.7 μm and generates light.
The main element of the active layer is composed of Ga, In, N, and As
Layer or a layer made of Ga, In, As, and a laser
Provided at the top and bottom of the active layer to obtain light
Surface-emitting type semiconductor laser having a resonator structure including a reflector
The element chip, wherein the reflection mirror has a reflection wavelength of 1.1.
When the refractive index of the material layer constituting the reflecting mirror is larger than μm,
Periodically changes to different values, and the incident light is reflected by light wave interference.
A semiconductor distributed Bragg reflecting mirror,
The material layer with a small refractive index is Al _xGa_1-xAs (0 <x ≦
1) and the material layer having a large refractive index is Al_yGa_{1 -Y}
As (0 ≦ y <x ≦ 1), and the refractive index is small and large.
Al whose refractive index takes a value between small and large between the material layers of_z
Ga_1-zHetero consisting of As (0 ≦ y <z <x ≦ 1)
A spike buffer layer having a thickness of 20 nm to 50 nm
Launches a surface-emitting type semiconductor laser device chip that is a mirror
The light source is an optical fiber or optical waveguide.
Core diameter X, opening diameter d of semiconductor laser, light of semiconductor laser
Assuming the radiation angle θ, the optical fiber or
The optical path length l to the end of the optical waveguide is d + 2ltan (θ / 2)
An optical communication system satisfying ≦ X. 2. A laser chip connected to the laser chip.
In an optical communication system, the laser chip
The wavelength is 1.1 μm to 1.7 μm, and the light generating activity
A layer in which the main element of the active layer is Ga, In, N, As,
Alternatively, a layer made of Ga, In, or As is used, and laser light is
Reflections provided above and below the active layer to obtain
Surface-emitting type semiconductor laser device having a cavity structure including a mirror
A reflecting chip having a reflection wavelength of 1.1 μm
Above, the refractive index of the material layer that constitutes it is different from the small and large values
The half that changes periodically and reflects the incident light by light wave interference
A conductor distributed Bragg reflector, and the refractive index is
Small material layer is Al_xGa _1-xAs (0 <x ≦ 1)
The material layer having a large refractive index is made of Al_yGa_1-yAs
(0 ≦ y <x ≦ 1), wherein the active layer is
The main composition between the reflectors is Ga_xIn_1-xP_yA
s_1-yNon-light-emitting layer (0 <x ≦ 1, 0 <y ≦ 1)
Surface-emitting type semiconductor laser device having a recombination prevention layer
Optical fiber or optical fiber
The core diameter X of the waveguide, the aperture diameter d of the semiconductor laser, the semiconductor laser
If the light emission angle θ of the laser is
The optical path length l to the end of the optical waveguide or the optical waveguide is d + 2ltan
An optical communication system characterized by satisfying (θ / 2) ≦ X
M 3. The optical communication system according to claim 1, wherein the semiconductor laser and the optical fiber or the optical waveguide are in contact with each other. 4. The optical communication system according to claim 1, wherein the optical fiber or the optical waveguide has a heat radiating part, and the heat radiating part is in contact with the semiconductor laser element chip. 5. The optical communication system according to claim 1, wherein a plurality of said optical fibers or optical waveguides and said plurality of semiconductor laser devices are provided.