JP2000323787A - Light emitting device module - Google Patents

Abstract

(57) [Problem] To provide a light-emitting element module which can output light with high monochromaticity and rarely causes chirping. SOLUTION: The light emitting element module 10 is configured by combining a semiconductor light emitting element 12 and an optical fiber 14 having a built-in diffraction grating 44. The semiconductor light emitting device 12 is configured by sequentially laminating a lower cladding layer 18, an active layer 20 acting as a waveguide, and an upper cladding layer 22 on the upper surface of a substrate 16. The active layer 20 is a superlattice structure formed by laminating a barrier layer 20b made of the quantum well layer 20a and the InP consisting of Ga _0.54 In _{0. 46} As alternately, the quantum well layer 2
0a is given a tensile strain in the laminating direction. Further, the emission surface 12a of the semiconductor light emitting element 12 forms an acute angle with respect to the lamination direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device module, and more particularly, to a light emitting device module comprising a semiconductor light emitting device and an optical fiber having a built-in diffraction grating. The present invention relates to a light-emitting element module comprising a resonator.

[0002]

2. Description of the Related Art A light emitting device module in which an optical fiber having a built-in diffraction grating is arranged so as to face an emission surface of a semiconductor light emitting device is widely used because it has a relatively stable spectrum with a simple structure. .

In such a light emitting device module, the reflection surface (surface facing the emission surface) of the semiconductor light emitting device and the diffraction grating in the optical fiber constitute a Bragg reflector type resonator. Light of a specific wavelength determined by the grating period oscillates, and this light is output as output light of the light emitting element module.

Further, the active layer of the semiconductor light emitting device has a superlattice structure in which a quantum well layer and a barrier layer are stacked, so that the emission spectrum width of output light can be narrowed and monochromaticity can be improved.

[0005]

However, the light emitting element module according to the above prior art has the following problems. That is, the light output from the semiconductor light-emitting element has a TM wave having an electric field component in the stacking direction of the quantum well layer and the barrier layer and an electric field component in a direction perpendicular to the stacking direction (a direction in which the quantum well layer spreads). The active layer has a TE wave, but the TE wave is usually the main component due to the structure of the active layer.

On the other hand, in semiconductor materials, a plasma effect in which carriers (electrons) vibrate due to an electric field of light is known. Here, in the semiconductor light emitting device used in the light emitting device module according to the related art, as described above, since the TE wave having the electric field component in the direction in which the quantum well layer spreads is the main component, the quantum well layer Within the carrier, the carrier vibrates greatly and polarization occurs. Such polarization causes a change in the refractive index of the laser medium, and as a result, widens the emission spectrum width of the output light and causes chirping and the like.

Accordingly, an object of the present invention is to provide a light emitting device module which can solve the above-mentioned problems and can output light with high monochromaticity and is less likely to cause chirping.

[0008]

In order to solve the above problems, a light emitting device module according to the present invention comprises a semiconductor light emitting device and an optical fiber having a built-in diffraction grating. A light emitting device module that forms a resonator between a lattice and a semiconductor light emitting device has an active layer in which a quantum well layer and a barrier layer are stacked, and a quantum well layer is stacked in the quantum well layer. It is characterized in that tensile strain is given in the in-plane direction (the direction in which the quantum well layer spreads).

By giving the tensile strain in the in-plane direction to the quantum well layer, it is possible to output light mainly composed of TM waves. Here, since the TM wave has an electric field component in the stacking direction, the carrier may oscillate in the stacking direction due to the plasma effect. However, since the quantum well layer is usually formed to be extremely thin, the oscillation range of carriers is also limited to an extremely narrow (thin) region. Therefore, the change in the refractive index due to polarization is also extremely small.

In the light emitting device module according to the present invention, the tensile strain may be given by shifting the composition of the semiconductor forming the quantum well layer from a state of lattice matching.

By shifting the composition of the semiconductor forming the quantum well layer from the state of lattice matching, tensile strain can be given to the quantum well layer.

In the light emitting device module of the present invention, among the end surfaces of the semiconductor light emitting device, the end surface facing the optical fiber has an acute angle with respect to the stacking direction in which the quantum well layer and the barrier layer are stacked. It may be characterized by doing.

By making the end face an acute angle with respect to the laminating direction, the reflectance at the end face can be reduced.

Further, in the light emitting element module according to the present invention, the angle may be such that an incident angle of light incident on the end face from inside the semiconductor light emitting element is a Brewster angle. .

By making the above angle a Brewster angle,
The reflectance of the p-polarized light at the end face can be made zero. Here, in the case where a TM strain is the main component by applying tensile strain to the quantum well layer, the main component of light incident on the end face from inside the semiconductor light emitting element is p-polarized light. Therefore, by making the reflectance of p-polarized light zero,
The reflectance at the end face can be extremely reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light emitting device module according to an embodiment of the present invention will be described. First, the configuration of the light emitting element module according to the present embodiment will be described. FIG.
FIG. 1 is a perspective view of a light emitting element module according to the present embodiment (a part of the light emitting element module is notched).

As shown in FIG. 1, the light emitting element module 10 has a configuration in which a semiconductor light emitting element 12 and an optical fiber 14 are combined.

The semiconductor light emitting device 12 includes a lower cladding layer 18, an active layer 20 acting as a waveguide, and an upper surface ((100) surface) of a substrate 16 made of Sn-doped n-type InP and having a thickness of about 90 μm. The upper clad layer 22 has a laminated structure.

The lower cladding layer 18 is made of n-type InP, and is formed in a strip shape on the upper surface of the substrate 16. Further, the lower cladding layer 18 has a thickness of about 0.5 μm.

The active layer 20 is made of Ga, as shown in FIG.
A quantum well layer 20a made of _0.54 In _0.46 As and having a thickness of about 10 nm is made of InP and having a thickness of 7 nm.
Ten layers are laminated via a barrier layer 20b of about nm, and the laminated structure is sandwiched between InP layers 20c of about 50 nm in thickness.

Here, in order to lattice match the quantum well layer 20a with InP, the quantum well layer 20a is made of, for example, Ga.
_Although it is necessary to have a composition of about _0.47 In _0.53 As, here, a tensile strain is applied to the quantum well layer 20 a in the stacking direction of the quantum well layer 20 a and the barrier layer 20 b.
The composition of the quantum well layer 20a is Ga _0.54 In _0.46 As. With such a composition, the mismatch rate is about 0.5%.

The upper cladding layer 22 is made of p-type InP and is formed on the active layer 20. The upper cladding layer 22 has a thickness of about 0.4 μm. Here, the active layer 20 sandwiched between the lower cladding layer 18 and the upper cladding layer 22 functions as a waveguide of the semiconductor light emitting device 12.

The lower clad layer 1 formed in a belt shape
8, on both sides of the active layer 20 and the upper cladding layer 22,
As shown in FIG. 1, a p-type InP layer 24a having a thickness of about 0.5 μm and an n-type IP layer having a thickness of about 0.5 μm
The current blocking layer 24 in which the nP layers 24b are stacked is provided. Further, an isolation groove 26 for element isolation is provided outside the current blocking layer 24 in parallel with the optical axis of the waveguide.

On the upper surfaces of the upper cladding layer 22 and the current blocking layer 24, a cladding layer 28 made of p-type InP having a thickness of about 1.5 μm is provided so that light does not reach a contact layer (described later). And the cladding layer 28
Also has the function of flattening the boundary between the non-flat upper cladding layer 22 and the current blocking layer.

On the upper surface of the cladding layer 28, p-type GaIn
A contact layer 30 made of As and having a thickness of about 0.5 μm is provided, and an upper surface electrode 32 having a three-layer structure in which a Ti layer, a Pt layer, and an Au layer are stacked from the contact layer 30 side on the upper surface of the contact layer 30. Is formed, and
On the lower surface of the substrate 16, a Ti layer, AuGe
A lower electrode 34 having a five-layer structure in which a layer, a Ni layer, a Ti layer, and an Au layer are stacked is formed. Here, in a portion corresponding to the upper part of the active layer 20, the contact layer 30 and the upper surface electrode 3
2 are in contact with each other but do not correspond to the upper part of the active layer 20.
An insulating layer 36 made of iN is provided.
And the upper electrode 32 are electrically insulated. further,
A gold plating layer 38 (2.5 μm thick) serving as an electrode is provided on the upper surface of the contact layer 30.

Of the end faces of the semiconductor light emitting element 12, the end face on the side facing the optical fiber 14 (hereinafter referred to as the emission face 12a) has an acute angle with respect to the laminating direction of the quantum well layer 20a and the barrier layer 20b. No. More specifically, they are arranged so that the angle of incidence of light entering the emission surface 12a from inside the semiconductor light emitting element becomes the Brewster angle. That is, the angle between the extending direction of the band-shaped active layer 20 and the normal direction of the emission surface 12a is 15.9 ° (the angle between the bottom surface of the semiconductor light emitting element 12 and the emission surface 12a is 74.degree.).
1 °). In addition, a low-reflection film 40 made of SiN is formed on the emission surface 12a of the semiconductor light emitting element 12 in order to reduce the reflectance on the emission surface 12a.

On the other hand, the other end surface of the semiconductor light emitting element 12 (hereinafter, referred to as a reflection surface 12b) is formed by cleavage so as to be perpendicular to the direction in which the band-shaped active layer 20 extends. The reflection surface 12b is provided with a high reflection film 42 in which two layers of a film made of SiN and a film made of α-Si are alternately laminated in order to increase the reflectance on the reflection surface 12b. .

The optical fiber 14 is provided with its end 14 a facing the active layer 20 on the light emitting surface 12 a of the light emitting element 10. Specifically, the optical axes are aligned so that the optical axis of the optical fiber 14 matches the optical axis of the light emitted from the emission surface 12a of the light emitting element. The core 43 of the optical fiber 14 is provided with a diffraction grating 44 at a position separated by a predetermined distance from the end 14a.
Optical resonance can be generated with the reflection surface 12b of the light emitting element 10 via the zero waveguide.
The tip of the optical fiber 14 is processed into a substantially spherical shape so that the light emitted from the emission surface 12a of the semiconductor light emitting element 12 is efficiently incident on the core of the optical fiber 14. Here, the emission surface 12a of the semiconductor light emitting element 12 and the optical fiber 1
4 and the end 14a of the optical fiber 14.
The distance between the diffraction grating 44 and the diffraction grating 44,
It can be adjusted appropriately so as to obtain a desired resonance frequency. The laser light generated by this resonance is transmitted through the optical fiber 14 and output from the other end of the optical fiber 14.

Next, a method for manufacturing the semiconductor light emitting device 12 used in the light emitting device module according to the present embodiment will be described.

In order to manufacture the semiconductor light emitting device 12, first, as shown in FIG. 3, a lower cladding layer 18, an active layer 20, and an upper cladding layer 22 are sequentially formed on the entire upper surface of a substrate 16 by the OMVPE method. And the upper cladding layer 22
A cap layer 46 made of p-type GaInAs and protecting the lower layer is formed to a thickness of about 0.2 μm by OMVPE on the entire upper surface of the substrate.

Subsequently, an insulating layer 48 made of, for example, SiN is formed on the upper surface of the cap layer 46 by a plasma CVD method (about 0.1 μm in thickness), and a photoresist is applied on the insulating layer 48. This photoresist is exposed using a mask having a band-shaped (3.5 μm width) pattern, and a substantially linear waveguide pattern covered with the photoresist is formed on the insulating layer 48. Thereafter, wet etching is performed using a solution containing hydrofluoric acid as a main component, using the photoresist left by the exposure as a mask. By this etching, the insulating layer 48 at a portion other than immediately below the substantially straight waveguide pattern is removed.

Thereafter, the photoresist is peeled off, and wet etching is performed using a mixed solution of bromine and methanol with the remaining portion of the insulating layer 48 as a mask. Here, etching removal is performed to a depth of about 2 μm, and as a result, as shown in FIG. 4, the cap layer 46, the upper cladding layer 22, the active layer 20, and the lower cladding layer 18 are removed, and a strip extending substantially linearly is formed. Is formed. Here, since the cap layer 46 is appropriately side-etched, the cross section of the mesa does not become an inverted mesa, and a substantially square shape close to a normal mesa can be obtained.

Subsequently, as shown in FIG. 5, the insulating layer 48 left in the above process is used as a mask on both sides of the lower cladding layer 18, the active layer 20, and the upper cladding layer 22 formed in a strip shape. The p-type InP layer 24 is formed by selective burying growth.
a, the n-type InP layer 24b is sequentially grown to form the current blocking layer 2
4 is formed.

Thereafter, the remaining insulating layer 48 is removed with hydrofluoric acid, and the cap layer 46 is removed with a hydrochloric acid-based solution. As shown in FIG. 6, the entire upper surfaces of the upper cladding layer 22 and the current blocking layer 24 are removed. Next, a cladding layer 28 is grown, and then a contact layer 30 is formed.

After the formation of the contact layer 30, an isolation groove 26 for element isolation is formed as shown in FIG. Specifically, first, an insulating layer 50 made of, for example, SiN is formed to a thickness of 0.1 μm on the entire upper surface of the contact layer 30 by a plasma CVD method, and a photoresist is applied on the insulating layer 50. Thereafter, the photoresist is exposed using a mask having a pattern of a separation groove to be formed (for example, a width of 10 μm), and a pattern of the separation groove (a pattern in which the photoresist is removed only in the part of the separation groove) is formed on the insulating layer 50. ) Is formed. The pattern of the separation groove is formed as two band-shaped patterns arranged on both sides of the waveguide and parallel to the waveguide. By performing selective etching using the insulating layer 50 left in the above process as a mask, two isolation grooves 26 are formed on both sides of the waveguide. Here, a mixed solution of bromine and methanol is used for the etching.

Subsequently, the insulating layer 50 used as a mask is removed, and as shown in FIG. 8, the upper surface of the contact layer 30 which does not correspond to the upper part of the waveguide, and the separation groove 2
An insulating layer 36 is formed on the inner wall portion of No. 6. Specifically, after the insulating layer 36 is formed on the upper surface of the contact layer 30 and the inner wall portion of the separation groove 26 by the plasma CVD method,
A portion of the insulating layer 36 corresponding to the upper part of the waveguide (width of about 1
0 μm) is removed by etching.

Thereafter, as shown in FIG. 9, the upper surface of the insulating layer 36 and the portion of the upper surface of the contact layer 30 corresponding to the upper portion of the waveguide (that is, the portion where the insulating layer 36 is not formed) are formed. The upper electrode 32 is formed by vapor deposition so as to cover it.

Subsequently, as shown in FIG.
Is plated with Au to form an Au plating layer 3
8 is formed, and the substrate 16 is formed by grinding and polishing.
After the thickness of the substrate 16 is reduced to about 90 μm, a lower electrode 34 is formed on the entire lower surface of the substrate 16 by vapor deposition, as shown in FIG.

Thereafter, element separation is performed by cleavage and scribe division as shown in FIG. After the element separation, one of the cleavage planes is chemically etched with a phosphoric acid-based or sulfuric acid-based solution to form the low-reflection film 40, thereby forming the incident surface 12a. Also, by forming the high reflection film 42 on the other cleavage plane, the reflection surface 12b is formed.

Next, the operation and effect of the light emitting element module according to the present embodiment will be described. The light emitting element module 10 according to the present embodiment includes a quantum well layer 20a.
By applying a tensile strain to the quantum well layer 20a in the in-plane direction, light having a TM wave as a main component can be output. Here, since the TM wave has an electric field component in the laminating direction, it is considered that the carrier vibrates in the laminating direction due to the plasma effect. The oscillation range is also limited to an extremely narrow region, and the change in the refractive index due to polarization is extremely small. As a result, it becomes possible to output light with high monochromaticity, and it is possible to prevent occurrence of chirping.

It is possible to output light mainly composed of TM waves by applying tensile strain for the following reasons. That is, when there is no distortion, the valence band is degenerated into a light hole band LH and a heavy hole band HH at the wave number k = 0.

Here, the optical gain corresponds to an integral of the product of the density of states of the conduction band and each hole band (hereinafter referred to as a band) and the Fermi distribution function calculated from the energy level. . Therefore, when calculating the optical gain for each of the TM wave and the TE wave, the above products may be added for the bands that contribute to each of the TM wave and the TE wave. Here, the LH band mainly contributes to the TM wave, and the HH band mainly contributes to the TE wave.

In the state of the lattice matching system where no distortion is given, or in the state where compressive strain is given,
Since the HH band mainly contributes to the optical transition and the HH band is at a low position as the energy of the hole, the TE wave becomes dominant. On the other hand, in a state where a tensile strain is given, the energy of holes in the LH band decreases, and the TM wave becomes dominant. For example, when 1.9% tensile strain is applied, compared with the case where no strain is applied,
The energy of holes in the LH band is reduced by about 150 meV. Therefore, while the TE wave has the same optical gain as that when no distortion is applied, the TM wave has about three times the optical gain when no distortion is applied. The waves become dominant. This is because the effective mass of the LH band mainly contributing to the TM wave is light and the state density is large.

The reason why the LH band is sensitive to distortion is as follows. That is, it is known that the top of the valence band of the III-V group compound semiconductor is a band derived from the d orbital of the group V atom. The bottom of the conduction band originates from the s orbital of the group III atom. Since the s orbit is a spherical object and an isotropic orbit, the s orbit is hardly affected by tension and compression. On the other hand, the d orbital of the isolated atom is degenerate fivefold, and each orbital is dxy, dy, respectively.
z, dzx, dx ² -y ² and dz ² . Here, the LH band mainly receives contribution from the dz ² orbit, and since the dz ² orbit has a vertically long shape in the z direction, it is considered that the dz ² orbit is sensitive to stretching and compression in the z direction. Here, the z direction refers to the lamination direction.

In the light emitting device module 10 according to the present embodiment, the tensile strain is given to the quantum well layer 20a by shifting the composition of the semiconductor forming the quantum well layer 20a from the state of lattice matching. Can be given relatively easily.

Further, in the light emitting device module 10 according to the present embodiment, the reflectance at the light emitting surface 12a can be reduced by making the light emitting surface 12a of the semiconductor light emitting device 12 an acute angle with respect to the lamination direction. Therefore, Fabry-Perot mode light generated between the emission surface 12a and the reflection surface 12b of the semiconductor light emitting element 12 can be reduced. As a result, the monochromaticity of the output light output from the light emitting element module 10 and the stability of the light output increase.

Further, in the light emitting element module 10 according to the present embodiment, by setting the above angle as the Brewster angle,
The reflectance of the p-polarized light on the emission surface 12a can be made zero. Here, when a tensile strain is applied to the quantum well layer 20a and the TM wave is the main component, the main component of the light incident on the emission surface 12a from inside the semiconductor light emitting element 12 is p
It becomes polarized light. Therefore, by setting the reflectance of the p-polarized light to zero, the reflectance at the emission surface 12a can be extremely reduced. As a result, it is possible to output stable light having extremely high monochromaticity from the light emitting element module 10.

In the light emitting element module 10 according to the above embodiment, the angle between the light emitting surface 12a and the normal direction is 15.9.
°, the bottom surface of the semiconductor light emitting element 12 and the emission surface 12a.
Was set to 74.1 °, which is the same as FIG.
As shown in FIG.
light emitting element module 6 having an angle of 74.1 ° with a
It may be something like 0.

[0049]

According to the light emitting device module of the present invention, by applying a tensile strain to the quantum well layer in the direction of lamination of the quantum well layer and the barrier layer, light having a TM wave as a main component can be output. it can. Here, since the TM wave has an electric field component in the laminating direction, it is considered that the carrier vibrates in the laminating direction due to the plasma effect. The oscillation range is also limited to an extremely narrow region, and the change in the refractive index due to polarization is extremely small. As a result, it becomes possible to output light with high monochromaticity, and it is possible to prevent occurrence of chirping.

In the light emitting device module of the present invention, the tensile strain is given to the quantum well layer by shifting the composition of the semiconductor forming the quantum well layer from the state of lattice matching, thereby relatively reducing the tensile strain. Can be easily given.

Further, in the light emitting device module of the present invention, of the end surfaces of the semiconductor light emitting device, the end surface facing the optical fiber is formed at an acute angle with respect to the lamination direction, so that the reflectance at the end surface is reduced. it can. As a result, Fabry-Perot light generated between both end faces of the semiconductor light emitting element can be reduced, and the monochromaticity of the output light output from the light emitting element module increases.

Further, in the light emitting element module of the present invention, by setting the angle as the Brewster angle, the reflectance of p-polarized light on the end face can be made zero. As a result, it is possible to output light with extremely high monochromaticity from the light emitting element module.

[Brief description of the drawings]

FIG. 1 is a perspective view of a light emitting element module.

FIG. 2 is a diagram showing a cross-sectional structure of an active layer.

FIG. 3 is a manufacturing process diagram of the light emitting element module.

FIG. 4 is a manufacturing process diagram of the light emitting element module.

FIG. 5 is a manufacturing process diagram of the light emitting element module.

FIG. 6 is a manufacturing process diagram of the light emitting element module.

FIG. 7 is a manufacturing process diagram of the light emitting element module.

FIG. 8 is a manufacturing process diagram of the light emitting element module.

FIG. 9 is a manufacturing process diagram of the light emitting element module.

FIG. 10 is a manufacturing process diagram of the light emitting element module.

FIG. 11 is a manufacturing process diagram of the light-emitting element module.

FIG. 12 is a manufacturing process diagram of the light emitting element module.

FIG. 13 is a perspective view of a light emitting element module.

[Explanation of symbols]

10, 60: light emitting element module, 12, 62: semiconductor light emitting element, 14: optical fiber, 16: substrate, 18: lower cladding layer, 20: active layer, 22: upper cladding layer, 2
4 ... current blocking layer, 26 ... separation groove, 28 ... cladding layer, 3
0: contact layer, 32: upper electrode, 34: lower electrode,
36, 48, 50: insulating layer, 38: Au plating layer, 40
... low reflection film, 42 ... high reflection film, 44 ... diffraction grating, 46 ...
Cap layer

Claims (4)

[Claims] 1. A light emitting device module comprising: a semiconductor light emitting device; and an optical fiber having a built-in diffraction grating, wherein a semiconductor light emitting device and a diffraction grating constitute a resonator. The device has an active layer in which a quantum well layer and a barrier layer are stacked, and the quantum well layer is given a tensile strain in an in-plane direction in which the quantum well layer is stacked. Light emitting element module. 2. The light emitting device module according to claim 1, wherein the tensile strain is given by shifting a composition of a semiconductor forming the quantum well layer from a state of lattice matching. 3. An end face of the semiconductor light emitting device, the end face facing the optical fiber, forming an acute angle with a stacking direction in which the quantum well layer and the barrier layer are stacked. The light-emitting device module according to claim 1, wherein the light-emitting device module is a light-emitting device module. 4. The light emitting device module according to claim 3, wherein the angle is an angle at which an incident angle of light incident on the end face from inside the semiconductor light emitting device becomes a Brewster angle. .