JPH06260727A - Optical semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance an MQW structure in band gap energy difference making the best use of the feature of an MOVPE method wherein semiconductor is not etched when a semiconductor optical integrated circuit, in which optical waveguide regions of MQW structure different in band gap energy are integrated in the direction of an optical waveguide, is formed through an MOVPE selective growth method. CONSTITUTION:An MQW layer 5 is selectively formed in a region small in ban gap energy (Eg) using an insulating film striped mask but formed on all region large in band gap energy (Eg). A clad layer 7 is selectively formed so as to cover an MQW structure in a region of large Eg but to constitute a ridge waveguide structure in a region of small Eg using a striped mask formed on both the regions. Therefore, an Eg difference can be increased, and an optical semiconductor device can be improved in characteristics without employing a method wherein semiconductor is etched. Moreover, a device can be integrated together with a curved optical waveguide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention integrates a semiconductor laser unit used for optical communication, optical information processing, etc., or a semiconductor laser and a semiconductor optical modulator, a semiconductor optical amplifier, a semiconductor optical waveguide, etc., on the same substrate. The present invention relates to a method for manufacturing an optical semiconductor device.

[0002]

2. Description of the Related Art A semiconductor laser alone has been developed as a light source used for optical communication, optical information processing, etc. Recently, in addition to semiconductor lasers, semiconductor lasers have been developed for the purpose of retaining more advanced functions. Research and development of semiconductor optical integrated circuits in which various types of semiconductor optical functional devices such as modulators, semiconductor optical amplifiers, and semiconductor optical waveguides are monolithically integrated on the same substrate have become active.

Since the semiconductor optical integrated circuit is an integrated structure of optical semiconductor elements having different bandgap energies (Eg) and the manufacturing method is complicated, there is a problem that the yield and uniformity of element characteristics are deteriorated. In order to overcome such a problem, a manufacturing method by selective growth using a dielectric thin film stripe mask is disclosed in Japanese Patent Application Laid-Open No. 4-105383 (Japanese Patent Application No. 2-222928).

As shown in the surface view of FIG. 4A and the sectional view of FIG. 4B, a pair of dielectric thin film stripe masks 2 are formed on the surface of an InP semiconductor substrate 1 having a (100) plane orientation.
0 (width Wm, spacing Wg) is formed, and a multiple quantum well (M) including an InGaAs quantum well in a waveguide region 21 sandwiched between masks 20 by a metal organic chemical vapor deposition method (MOVPE method) is formed.
By growing the QW) structure 5, an active layer of a semiconductor laser can be formed without using a semiconductor mesa etching step. Therefore, the uniformity of the device structure is improved. Further grown InGa
Since the layer thickness and mixed crystal composition of the As well change depending on Wm, as shown in FIG. 4C, the bandgap energy Eg (or emission wavelength) of the MQW structure is changed to the mask width W.
It can be changed by m.

By utilizing the Eg control by the MOVPE selective growth, the connection structure of the optical waveguide structure having different Eg can be produced by one crystal growth, the yield of the semiconductor optical integrated circuit is improved, and the conductivity is improved. High coupling efficiency between the waveguides can be obtained. FIG. 5 shows an example of manufacturing a distributed Bragg reflector (DBR) semiconductor laser having a wavelength variable mechanism (see Japanese Patent Application No. 3-067498). FIG. 5C shows a sectional view of the element. First, the (100) orientation n-InP substrate 1
A grating is formed in the upper DBR region 33 (FIG. 5A). Next, the n-InGaAsP guide layer 2 and n
After growing the —InP spacer layer 3 on the entire surface, FIG.
As shown in the front view, a pair of SiO ₂ stripe masks 20 are formed on the surface in the [011] direction at a constant interval Wg 1. At this time, the mask width is Wm 1 in the active region 31,
In the phase control area 32 and the DBR area 33, Wm 1 ′
(Wm 1> Wm 1 ′). Then, the n-InP clad layer 4, the MQW active layer 5, and the p-InP clad layer 6 are provided in the waveguide region 21 sandwiched between the stripe masks 20.
Select to grow.

Next, as shown in FIG. 5B, the opposite side edge portions of the stripe mask 20 are partially removed to expand the waveguide region width to Wg 2, and the growth region 23 is provided with p-InP.
The cladding layer 7 and the p-InGaAs (P) cap layer 8 are selectively grown. When the growth pressure is 76 Torr, the mask width is Wm 1 = 10 μm, and Wm 1 ′ = 4 μm, the emission peak wavelengths from the MQW layer 5 in the active region 31 and the DBR region 33 are 1.55 μm and 1.
It is 50 μm, and a wavelength difference of about 50 nm is obtained between the two. For example, OFC 1992 Lecture Paper F
See B10 (T. Sasaki et al., Op.
tial fiber communication
Conference, San Jose, U.S.A. S.
A. , 1992, Paper FB10).

In the device structure shown in FIG. 5, the DBR having a large Eg is used.
Also in the region 33, the MQW layer 5 was selectively formed in the region sandwiched by the SiO ₂ stripe masks 20.

On the other hand, FIG. 6 shows an example in which an integrated light source of a distributed feedback (DFB) semiconductor laser and a semiconductor optical modulator is constructed, which is described in Electronics Letters, Vol. 27, page 2138. (M. Aoki et al., Elec
tronics Letters, Vol. 27, p
p. 2138, 1991). Here, in the optical modulator region 38 having a large Eg, the MQW structure is formed over the entire surface. A sectional view is shown in FIG. As a manufacturing method, as shown in the surface view of FIG.
On the n-InP substrate 1 in which the O ₂ stripe mask 20 (width Wm 1, spacing Wg 1) and the grating 24 are formed only in the DFB laser region 34, n-InGaAsP is formed.
The guide layer 2, the n-InP spacer layer 3'MQW active layer 5, and the p-InP clad layer 6 are grown. Next in FIG.
As shown in the surface view in (b), one SiO ₂ stripe mask 22 (width Wa,
Wa <Wg 1) is formed, and mesa etching is performed up to the substrate 1 using an etching solution to form a waveguide structure having a width Wa. After the p-InP current blocking layer 9 and the n-InP current blocking layer 10 are embedded and grown using the stripe mask 22, the p-InP cladding layer 7 and the p-InGaAs (P) cap layer 8 are grown on the entire surface. In this example, the waveguide structure is a buried hetero (BH) structure which has been often used conventionally.

Further, in manufacturing a semiconductor optical amplifier which is important in an optical fiber communication system and the like, it is important to suppress the end face reflectance. As an effective method to reduce the reflectance,
There is a window structure in which the waveguide layer is interrupted at the end face and the end face is filled with a semiconductor layer having a large band gap energy. See IOAC 1989 Lecture Paper 20C2-2.
(I. Cha et al., 100C'89, Kob.
e, paper 20C2-2). Further, as a method of forming a window structure by using selective growth, a method of forming a mask in a window region so that a waveguiding layer is not formed and then embedding a clad layer is applied (Japanese Patent Application No. 21
No. 6027).

[0010]

The device manufacturing method shown in FIGS. 5A and 5B does not use semiconductor etching, and the MQW
The active layer and the InP clad layer can be formed by selective growth, and a uniform structure can be obtained, so that the uniformity of device characteristics and the yield can be improved. However, even in the area of large Eg, the stripe mask 2
Since the MQW structure is formed by selective growth using 0, the Eg difference that can be obtained as shown in FIG. 4 (c) is limited, and when integrating an optical waveguide into a semiconductor laser, the optical waveguide is limited. However, there is a problem in that the Eg of is not sufficiently large and a sufficiently low waveguide loss cannot be obtained.

On the other hand, the device manufacturing method shown in FIG. 6 is characterized in that a relatively large Eg difference can be obtained because the MQW layer 5 is entirely grown in the region where the Eg is large. However, since the conventional semiconductor mesa etching process is included, the process is complicated, and the device characteristics tend to vary due to variations in the active layer width.

Further, in the semiconductor optical amplifier in which the window region is formed by the selective growth, there is a problem that the edge portion of the selectively formed waveguide layer is difficult to be smoothly embedded.

[0013]

A method for manufacturing an optical semiconductor device for solving the above-mentioned problems is a semiconductor substrate on which a first optical waveguide layer is formed over the entire surface thereof. The second optical waveguide layer is formed in a stripe shape and is formed on the entire surface in another region without interruption, and the semiconductor clad layer further covers the second optical waveguide layer formed in a stripe shape. Further, the optical semiconductor element is characterized in that the second optical waveguide layer formed on the entire surface is formed so as to have a stripe-shaped convex portion, respectively.

Alternatively, the layer thickness of the first optical waveguide layer is constant throughout, whereas the layer thickness of the quantum well layer is thicker in the stripe-shaped region than in other regions. Is an optical semiconductor element.

Alternatively, a step of crystal-growing a semiconductor multilayer film including a first optical waveguide layer on the entire surface of a semiconductor substrate, a step of locally forming two opposing first dielectric thin film stripes, and at least a quantum The second optical waveguide layer including the well structure is selectively grown in the growth regions inside the first dielectric thin film stripes facing each other, and at the same time, is entirely grown in the regions where the first dielectric thin film stripes are not formed. And a step of removing the first dielectric thin film stripe,
The two second dielectric thin film stripes facing each other are formed into the first
A step of forming the second optical waveguide layer formed in a region sandwiched between the dielectric thin film stripes so as to sandwich the second optical waveguide layer, and
In the growth region sandwiched between the second dielectric thin film stripes,
A method for manufacturing an optical semiconductor device, which comprises a step of selectively growing a semiconductor multilayer film including a semiconductor clad layer.

Alternatively, in the above method for manufacturing an optical semiconductor device, the first dielectric thin film stripe or the second dielectric thin film stripe is used.
A method for manufacturing an optical semiconductor element, characterized in that the stripe width of the dielectric thin film stripe is changed in the stripe direction.

Alternatively, in the above method for manufacturing an optical semiconductor device, the first dielectric thin film stripe or the second dielectric thin film stripe is used.
A method of manufacturing an optical semiconductor device, characterized in that the width of a growth region sandwiched between dielectric thin film stripes is changed in the stripe direction.

Alternatively, in the above method for manufacturing an optical semiconductor element, the second dielectric thin film stripe is formed in a curved shape in a part of the optical waveguide region. .

[0019]

In the MOVPE selective growth, the side surface of the selectively formed ridge structure has a very smooth crystal plane, so that the waveguide loss due to scattering is greatly reduced when the optical waveguide is manufactured. A low-loss ridge optical waveguide utilizing this feature has been proposed (Japanese Patent Application No. 3-01941).
No. 1). FIG. 7 shows the structure of the ridge optical waveguide. Figure 7
A sectional view is shown in FIG. I on the surface of the InP semiconductor substrate 1
After laminating the nGaAsP guide layer 2 and the InP spacer layer 3, as shown in the surface view of FIG.
_{A two-} stripe mask 22 (width Wm 2, spacing Wg 2) is formed, and the InP clad layer 7 is selectively grown in the sandwiched growth region 23. At this time, the plane orientation of the semiconductor substrate is set to (10
0), assuming that the direction of the stripe mask 22 is the [011] direction, the side surface of the selectively formed cladding layer 7 is a smooth (111) B plane. In the ridge optical waveguide manufactured in this way, extremely low waveguide loss is obtained.

When a semiconductor optical integrated circuit is manufactured by using the method for manufacturing an optical semiconductor element of the present invention, in the formation of the MQW layer, a stripe mask is not used in the region where Eg is large as in the example of FIG. Simultaneously with the formation on the entire surface, other regions with relatively small Eg are selectively formed using a stripe mask as in the example of FIG. In the subsequent formation of the waveguide structure, In is formed in the waveguide region in the same manner as in the example of FIG.
At the same time as forming the ridge waveguide structure by selectively growing the P layer, in the other regions, an InP clad layer is selectively formed so as to cover the MQW layer as in the example of FIG. Thus, by adopting only the advantages of the conventional example shown in FIGS. 5 to 7, a semiconductor optical integrated circuit having an MQW waveguide layer having a large Eg difference can be manufactured without using mesa etching of the semiconductor. . In the region where the MQW layer is grown on the entire surface, the layer thickness of the MQW layer is thin, and therefore another waveguide layer is previously grown on the entire surface in order to keep the propagation mode in the waveguide stable.

[0021]

EXAMPLES Examples of the semiconductor optical integrated device of the present invention will be described below.

FIG. 1 is a diagram showing a method of manufacturing a wavelength tunable DBR laser. 1 (a) and 1 (b) are surface views showing the pattern of the stripe mask in the first and second selective growths, respectively, and FIGS. 1 (c) and 1 (d) are the active regions after the completion of the crystal growth, respectively. It is sectional drawing which shows the structure of a DBR area | region. This device is manufactured by crystal growth three times.

First, D of (100) orientation n-InP substrate 1
A grating is formed on the BR region 33. Then, the n-InGaAsP guide layer 2 (layer thickness 100 n is formed on the entire surface).
m, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), n-InP spacer layer 3 (layer thickness 70 nm, carrier concentration 1 × 10 ¹⁸ cm 3
^-3 ) to grow. Next, as shown in FIG. 1A, a pair of SiO ₂ stripe masks 20 (width Wm 1 = 30 μm).
m, and an interval Wg 1 = 1.5 μm) is formed only in the active region 31 in the [001] direction. Then, the n-InP clad layer 4 (layer thickness 50 nm, carrier concentration 1 × 10 ¹⁸ c
m ^-3 ), MQW active layer 5 (7 layers of InGaAs well and InGaAsP barrier, and well thickness and barrier thickness are 7 nm and 15 nm, respectively), p-InP clad layer 6 (layer thickness 200 nm, carrier concentration 7 × 10). ¹⁷
cm ^-3 ).

The above-mentioned layer thickness is a value in the ridge structure selectively formed in the waveguide region 21 sandwiched between the stripe masks 20 of the active region 31, and in the phase control region 32 and the DBR structure 33 which are entirely grown. Layer thickness is about 1/3 of that
Becomes After removing the stripe mask 20,
As shown in FIG. 1 (b), a pair of SiO ₂ stripe masks 22 (width Wm 2 = 10 μm, interval Wg 2 = 6 μ) are provided again.
m) is formed in the entire region in the [011] direction with the waveguide region 21 at the center. And the p-InP clad layer 7
(Layer thickness 1.5 μm, carrier concentration 7 × 10 ¹⁷ cm ⁻³ ),
A p-InGaAs cap layer 8 (layer thickness 300 nm, carrier concentration 1 × 10 ¹⁹ cm ⁻³ ) is grown. All the layer thicknesses are values in the structure selectively formed in the growth region 23 sandwiched between the stripe masks 22.

As a result of this selective growth, FIG. 1 (c), (d)
As shown in, the p-InP clad layer 7 grows so as to cover the MQW layer in the active region 31, and is selectively formed in the phase control region 32 and the DBR region 33. That is,
The former has a structure similar to that of FIG. 5C, and the latter has a structure similar to that of FIG. 7B. The boundary between the two waveguide regions is formed without interruption. The growth pressure of the MQW active layer is 150 Tor.
It is growing at r, and as shown in FIG.
The shift amount of the emission peak wavelength due to the mask width is larger than that in the case of growing at rr. As a result, the active region and D
The emission peak wavelength in the BR region is 1.55 μm,
It became 1.40 μm. Conventionally, as shown in FIG. 5A, in the DBR region, the MQW structure is selectively formed in the region sandwiched by the mask with the width Wm 1 ′ = 4 μm, and the growth pressure is also 76 Torr. The wavelength is 1.
It was 50 μm.

As described above, the wavelength difference can be expanded from 50 nm to 150 nm by using the device manufacturing method of the present invention. After the crystal growth is completed in this way, SiO 2 is formed on the entire surface.
_Two films are formed, a stripe-shaped window is opened only on the waveguide region of each region, the p-side electrode is formed in a pattern on the p-InGaAs cap layer, and the n-side electrode is formed on the n-InP substrate. Was formed. Active region 31, phase control region 32
And the lengths of the DBR region 33 are 600 μm and 1 respectively.
The thickness was 50 μm and 300 μm.

As a result of evaluating the characteristics of the prototyped device, the threshold current was 9 mA on average, and an optical output of 30 mW or more was obtained. Further, by injecting a current up to 20 mA into the DBR region, it was possible to obtain a wavelength tunable width of 5 nm or more while keeping the optical output at 10 mW and accompanied by mode skipping. Furthermore, by injecting current up to 10 mA in the phase control region, it was possible to cover all wavelength regions in which mode skip occurred. In the conventional structure by selective growth (FIG. 5), the wavelength difference between the active region and the phase control region was not sufficient, so that even if current was injected into the phase control region, it could not be completely covered.

Since the wavelength difference can be widened by the present invention, a conventional three-electrode wavelength tunable DBR laser ', for example, Electronics Letters, Vol. 23, page 403 (1987) (S.
Murata et al. , Electronics
Letters, vol. 23, pp. 403, 19
In addition to realizing the quasi-continuous wavelength tunable operation similar to 87), it was possible to maintain the high yield and uniformity which are the features of the manufacturing method without using mesa etching of semiconductors. Second
An example will be described. FIG. 2A shows a DFB laser,
It is a surface view showing a mask pattern at the time of growth of an MQW structure of an element in which a semiconductor optical amplifier and an optical waveguide are integrated. Figure 1
As in (a), a pair of SiO ₂ stripe masks 20
Are formed only in the DFB region 34 and the semiconductor optical amplifier region 35. The layer structure of the element is the same as the example of FIG. 1, and the grating is formed only in the DFB region 34. As a result of device characteristic evaluation, an internal gain of the semiconductor optical amplifier of 20 dB and a waveguide loss of 15 cm ⁻¹ in the optical waveguide were obtained. Moreover, the coupling efficiency at the coupling part between the optical amplifier and the optical waveguide is 95.
The value was estimated to be over%.

As an example of the semiconductor optical amplifier according to the present invention, a waveguide layer is entirely grown in the window region to realize low end face reflectance without increasing loss in the window region.
Specifically, as shown in the surface view of FIG. 2B, the SiO ₂ stripe mask 20 is formed only on the active region 31 and M
A waveguiding layer having a QW structure is selectively formed in the waveguiding region 21, and is grown on the entire surface in the window region 37. Next, FIG.
As shown in the surface view of (c), a stripe mask 22 is formed on the entire surface, and a cladding layer is grown. At this time, the width Wg 2 of the growth region 23 sandwiched between the masks 22 is made wider in the window region 37 than in the active region 31, thereby reducing the internal loss in the window region. Fabricated active area length 300μ
m and an element having a window region length of 30 μm each, an internal gain of 25
A dB and end face reflectance of 10 ⁻⁵ were realized.

An embodiment of a semiconductor optical integrated circuit having a structure in which a tunable DBR laser and a semiconductor optical modulator are integrated for every two channels, and a semiconductor optical amplifier is connected using a multiplexer by a semiconductor optical waveguide will be described. FIG. 3 is a front view showing the manufacturing method. On the entire surface of the n-InP substrate 1 in which the grating is formed only in the DBR region 33, n-InG is formed.
aAsP guide layer 2 (layer thickness 100 nm, carrier concentration 1
× 10 ¹⁸ cm ^-3 ), n-InP spacer layer 3 (layer thickness 70
nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ).

Next, as shown in FIG. 3A, a pair of S
The iO ₂ stripe mask 20 is formed in the [011] direction in the active region 31, the optical modulator region 38, and the optical amplifier region 35. At this time, the mask width was 30 μm in the active region 31 and the optical amplifier region 35, and 15 μm in the light modulation region 38. The stripe mask 20 in the optical amplifier region is a set of the active region and the stripe mask 20 in the optical modulator region.
It is located in the middle position. In addition, the width of the waveguide region 21 in each region was fixed to 1.5 μm. The length of each area is
The active region is 600 μm, the DBR region is 150 μm, the optical modulator region is 200 μm, the optical waveguide region is 1500 μm, and the optical amplifier region is 300 μm.

Then, the n-InP clad layer 4 (layer thickness 5
0 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), MQW active layer 5 (7 layers of InGaAs well and InGaAsP)
The barrier layer has a well thickness and a barrier thickness of 7 nm and 15 nm, respectively, and the p-InP clad layer 6 (layer thickness 2).
00 nm, carrier concentration 7 × 10 ¹⁷ cm ⁻³ ). The above layer thickness is the same as the mask stripe 2 of the active region 31.
It is a value in the structure selectively formed in the waveguide region 21 sandwiched by zeros.

After removing the mask stripes 20 once, as shown in the front view of FIG.
O ₂ mask stripe 22 (width 10 μm, spacing 6 μm)
Are formed in the entire region with the waveguide region 21 at the center. At this time, a mask pattern is formed in a curved shape in the optical waveguide region 36 so that two adjacent optical modulators are connected to one optical amplifier, but the width of the ridge growth region 23 sandwiched by the mask is It is 6 μm constant in the entire region.
Then, the p-InP cladding layer 7 (layer thickness 1.5 μm, carrier concentration 7 × 10 ¹⁷ cm ⁻³ ), p-InGaAs cap layer 8 (layer thickness 300 nm, carrier concentration 1 × 10 ¹⁹ cm ³ ).
^-3 ) to grow. All the layer thicknesses are values in the structure selectively formed in the growth region 23.

That is, an integrated structure of a plurality of functional elements can be manufactured collectively by crystal growth three times by the same method as the manufacturing example of the DBR laser shown in FIG. In the present invention, since the optical waveguide has a ridge structure, it is possible to easily form a curved waveguide which has been difficult to manufacture in the past.

Pattern electrodes were respectively formed in the active region, the DBR region, the optical modulator region and the optical amplifier region, and the device characteristics were evaluated. As a result, an optical output of 20 mW or more was obtained for each channel from the end face on the optical amplifier side. Further, the extinction ratio is 15 dB when a voltage having an amplitude of 2 V is applied to the optical modulator section.
Was obtained, and a good modulated optical waveform was obtained at 2.5 Gb / s modulation. Further, the threshold current and the light output in 10 consecutive devices were 8 to 15 mA and 18 to 2 respectively.
It was 8 mW and the uniformity was good.

The present invention will be described in more detail with reference to the drawings showing the embodiments of the optical integrated device. FIG. 8A is a plan view of an optical integrated device in which a wavelength tunable DBR-LD, a Mach-Zehnder (MZ) optical modulator, an optical waveguide, a multiplexer, and an optical amplifier according to one embodiment of the present invention are integrated. . The variable wavelength DBR-LD 41 and the MZ optical modulator 42 are arranged in series on the same semiconductor substrate, and the output light from the MZ optical modulator 42 is guided by the waveguide 4.
At 3, the light is guided to the star coupler 44, which is a multiplexer, and is further collectively amplified by the optical amplifier 45. In order to realize such an element, the following may be done. That is, the insulating film masks 47 and 48 are partially formed on the portion where the wavelength tunable laser 41 and the optical amplifier 45 are formed on the semiconductor substrate 46 where the diffraction grating is partially formed. The diffraction grating is formed only in the DBR region 49. The mask width is wide in the portion where the active region 50 is formed, and narrow in the portion where the DBR region 49 is formed. Mask width is 15μm and 8μm respectively
And The wavelength composition of the MQW structure is 1.55 μm, 1.48 μm in the active region, the DBR region, and the flat portion, respectively.
It was 1.40 μm. It was confirmed that the composition in the flat portion was sufficiently transparent for the laser oscillation wavelength of 1.55 μm. The mask interval is 1.5 μm, and the embedded MQW waveguide layer can be automatically formed therein. The mask length is 400 μm for the active region and the DBR region,
It was set to 200 μm. In the optical amplifier 45, the width, length, and interval of the mask are 15 μm and 600 μm, respectively.
It was set to 1.5 μm. Substrate 4 on which a mask is formed in this way
On InGaAs, InGaAsP (wavelength composition 1.2
μm) multi-quantum well structure was grown. The film thickness was set to 60 A in each flat portion. The area between the masks 47 and 48 had a length of 2 mm. At this stage, the MQW waveguide is formed in the region between the masks so as to be included in the mesa structure, while it is formed flat in the region without the mask. A mask is formed again on the entire semiconductor structure thus obtained, a part of the mask to be the wavelength tunable LD 41 and the optical amplifier 45 is removed, and a cladding layer 51 is formed so as to cover the mesa structure. At this time, the portions forming the MZ optical modulator 42, the waveguide 43, and the star coupler 44 are patterned as shown in the figure to form the ridge 14 at the same time as the cladding layer 12. The width of the clad layer is 6 μm,
The width of the ridge 14 was 4 μm at the bottom. This makes D
The cross section of the BR-LD or the optical amplifier is shown in FIG.
In the embedded structure as shown in (b), the MZ optical modulator 42
The cross section of the portion has a ridge waveguide structure as shown in FIG. The phase modulator of the MZ optical modulator has a length of 600μ.
m, the curved waveguide 3 has a total length of 800 μm. In this embodiment, four DBR-LDs and four MZ optical modulators are monolithically integrated. A desired optical integrated device is obtained by partially forming electrodes on such a device.

In such a device, the oscillation threshold current of the DBR-LD was about 20 mA, the optical output was 10 mW, and the wavelength variable range was 5 nm. The MZ optical modulator operated at 3.5 V, and obtained an extinction ratio of about 15 dB at that time.
The total loss in the MZ optical modulator, the optical waveguide, and the star coupler is about 20 dB. By compensating for the loss by the optical amplifier, the chip optical output from each channel is + 8d.
A value of about Bm was obtained. Such an element is capable of transmitting an optical signal at a high speed of 10 Gb / s, for example, with a wavelength interval set to 4 nm, and is extremely useful as a light source for high-speed wavelength-multiplexed optical communication.

FIG. 9 is a diagram showing a manufacturing process of an integrated element of a wavelength tunable laser and an optical switch which is an embodiment of the present invention.
A mask 61 is partially formed as shown in FIG.
An InGaAsP-based MQW structure is grown on the substrate except for the mask portion. The wavelength composition of the MQW layer in the portion where the mask is formed and the flat portion is 1.55 μm,
It was 1.38 μm. A diffraction grating is formed in the portion where the mask is formed, and the DFB-LD 62 is formed.
The length of the mask was 400 μm, and the flat portion serving as the optical switch 63 had a length of 2 mm. An insulating film is formed on the entire surface and patterned as shown in FIG. An active waveguide having a buried structure is formed in a portion where the mask 61 has been formed in advance, and it can be operated as a DFB-LD having a buried structure. Further, a directional coupler type optical switch having a ridge waveguide structure can be formed in the portion where the mask is not formed. In the waveguide portion of the DFB-LD, the width of the active layer is 1.5 μm, the width of the buried layer is 8 μm,
In the optical switch part, the width of the ridge waveguide was 4 μm. By forming electrodes partially and further forming a Pt heating resistance wire on the DFB-LD, a resistance heating type wavelength tunable DFB-LD was obtained, and a desired optical integrated device was obtained.

By controlling the current flowing through the Pt resistance to about several tens of mA in such an element, a wavelength tunable operation in the range of about 4 nm can be obtained. Actually, a wavelength tunable DFB-LD having two wavelengths was formed. Resistance heating type DFB-
In the LD, the switching time for wavelength switching is several ms, and by setting them at a frequency interval of several tens GHz in advance and applying a voltage to the optical switch, 1
Switching can be performed with a switching time of about ns.

As described above, according to the present invention, the selected MOVPE
By skillfully applying the growth technology, it is possible to collectively form an embedded waveguide and a ridge-structured waveguide. Therefore, it is extremely useful for application to optical communication as shown in the embodiments. An integrated device can be realized.

In the embodiment of the present invention, the two-electrode DBR-LD and the resistance heating type DFB-LD are shown as the variable wavelength light source, but the present invention is not limited to these, and the three-electrode DFB-LD is used.
It is possible to use elements having various structures such as an LD, a three-electrode DBR-LD, a vertical coupling filter type wavelength tunable LD, and a composite resonator type wavelength tunable LD. Furthermore, although a directional coupler type optical switch is shown, the optical switch is not limited to this. Of course, the material system used is the InG shown here.
It is not limited to the aAsP system.

[0042]

As described above, the optical semiconductor device of the present invention has excellent characteristics and high yield. Further, by using the method for manufacturing an optical semiconductor device of the present invention, MOVPE
In the semiconductor optical integrated circuit manufactured by selective growth,
It has become possible to manufacture a device by expanding the bandgap energy shift amount of the MQW structure more than before without using the semiconductor mesa etching process. By using the present invention, the characteristics of the DBR semiconductor laser can be improved as compared with the conventional device using selective growth.
Further, the invention was also applied to the manufacture of various semiconductor optical integrated circuits having a structure in which optical semiconductor elements such as a semiconductor laser, a semiconductor optical modulator, and a semiconductor optical amplifier are integrated by using an optical waveguide, and a semiconductor optical amplifier having a window structure. Thus, by manufacturing a semiconductor optical integrated circuit, which has been conventionally manufactured by a complicated manufacturing method, by a simple method, it is possible to achieve both good device characteristics and high uniformity.

[Brief description of drawings]

FIG. 1 is a front view and a sectional view showing an embodiment of a method of manufacturing a distributed Bragg reflector semiconductor laser according to the first, second, and third aspects of the present invention.

FIG. 2 is an embodiment of a method for manufacturing a distributed feedback semiconductor laser, a semiconductor optical amplifier and an integrated device of an optical waveguide, and a semiconductor optical amplifier with a window structure according to claims 1, 2, 3, 4, and 5 of the present invention. FIG.

FIG. 3 is a surface view showing an embodiment of a method for manufacturing a semiconductor optical integrated circuit according to the present invention of claims 1, 2, 3, 4, and 6.

FIG. 4 is a diagram for explaining the action and effect of selective growth.

5A and 5B are a front view and a sectional view showing a method of manufacturing a distributed Bragg reflector semiconductor laser according to a conventional invention.

6A and 6B are a front view and a cross-sectional view showing a method of manufacturing an integrated light source of a distributed feedback semiconductor laser and a semiconductor optical modulator according to a conventional invention.

FIG. 7 is a front view and a cross-sectional view showing a method for manufacturing a ridge type optical waveguide according to a conventional invention.

FIG. 8: Tunable laser and Mach-Zehnder optical modulator,
It is a plan view of an optical integrated device in which an optical waveguide, a multiplexer, and an optical amplifier are integrated.

FIG. 9 is a diagram showing a manufacturing process of an integrated device of a wavelength tunable laser and an optical switch.

[Explanation of symbols]

1 n-InP substrate 2 n-InGaAsP guide layer 3 n-InP spacer layer 4 n-InP clad layer 5 MQW active layer 6 p-InP clad layer 7 p-InP clad layer 8 p-InGaAs (P) cap layer 9 p -InP block layer 10 n-InP block layer 20 SiO ₂ stripe mask 21 waveguide region 22 SiO ₂ stripe mask 23 growth region 24 grating 31 active region 32 phase control region 33 DBR region 34 DFB region 35 semiconductor optical amplifier region 36 optical waveguide Region 37 Window Region 38 Semiconductor Optical Modulator Region 41 Wavelength Variable DFB-LD 42 MZ Optical Modulator 43 Waveguide 44 Star Coupler 45 Optical Amplifier 46 Substrate 47 Mask 48 Mask 49 DFB Region 50 Active Region 51 Cladding Layer 52 Ridge 61 Mask 6 2 DFB-LD 63 Optical switch

Claims (7)

[Claims] 1. On a semiconductor substrate on which a first optical waveguide layer is formed on the entire surface, a second optical waveguide layer consisting of at least a quantum well layer is formed in a stripe shape in a certain region, while another region is continuously formed without interruption. Is formed on the entire surface,
Further, a semiconductor clad layer is formed so as to cover the second optical waveguide layer formed in a stripe shape and to form a stripe-shaped convex portion on the second optical waveguide layer formed over the entire surface. An optical semiconductor device characterized by the above. 2. The optical semiconductor element according to claim 1, wherein
While the layer thickness of the optical waveguide layer is constant throughout,
An optical semiconductor device, wherein the quantum well layer has a layer thickness that is thicker in a stripe-shaped region than in other regions. 3. A step of crystal-growing a semiconductor multilayer film including a first optical waveguide layer on the entire surface of a semiconductor substrate, and a step of locally forming two opposing first dielectric thin film stripes,
The second optical waveguide layer including at least a quantum well structure is provided in the first optical waveguide layer.
A step of selectively growing in opposite growth regions of the dielectric thin film stripe and at the same time growing entirely in a region where the first dielectric thin film stripe is not formed; and removing the first dielectric thin film stripe And a step of forming two opposing second dielectric thin film stripes on the entire surface of the substrate so as to sandwich the second optical waveguide layer formed in a region sandwiched by the first dielectric thin film stripes. A method for manufacturing an optical semiconductor device, which comprises the step of selectively growing a semiconductor multilayer film including a semiconductor clad layer in a growth region sandwiched by the second dielectric thin film stripes. 4. The method of manufacturing an optical semiconductor device according to claim 3, wherein the stripe width of the first dielectric thin film stripe or the second dielectric thin film stripe is changed in the stripe direction. Manufacturing method. 5. The method for manufacturing an optical semiconductor device according to claim 3, wherein the growth region width sandwiched between the first dielectric thin film stripe and the second dielectric thin film stripe is changed in the stripe direction. Method for manufacturing optical semiconductor device. 6. The method for manufacturing an optical semiconductor element according to claim 3, wherein the second dielectric thin film stripe is formed in a curved shape in a part of the optical waveguide region. . 7. A step of partially forming a first mask on a semiconductor substrate, and a step of forming an optical waveguide having a multiple quantum well structure by selective growth in a region other than the first mask on the substrate. A method for growing an optical semiconductor device, which comprises at least a step of performing selective growth after forming a second mask on the substrate and performing a desired patterning.