JP2814906B2 - Optical semiconductor device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single semiconductor laser, a semiconductor laser and a semiconductor optical modulator, a semiconductor optical amplifier, a semiconductor optical waveguide, etc., which are used for optical communication and optical information processing, and are integrated 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 and optical information processing, but recently, in addition to a semiconductor laser, a semiconductor laser has been developed in order to maintain more advanced functions. Research and development of semiconductor optical integrated circuits, in which various semiconductor optical functional elements such as modulators, semiconductor optical amplifiers, and semiconductor optical waveguides are monolithically integrated on the same substrate, have been activated.

A semiconductor optical integrated circuit is an integrated structure of optical semiconductor elements having different band gap energies (Eg), and has a problem that the yield and uniformity of element characteristics are reduced due to the complicated manufacturing method. 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 FIG. 4A and 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, interval Wg), and a multiple quantum well (M) including an InGaAs quantum well in a waveguide region 21 sandwiched between masks 20 by metal organic chemical vapor deposition (MOVPE).
By growing the QW) structure 5, it is possible to form an active layer of a semiconductor laser without using a semiconductor mesa etching step. Therefore, there is a feature that the uniformity of the element structure is improved. Further selective growth of InGa
Since the layer thickness and mixed crystal composition of the As well change depending on Wm, as shown in FIG. 4C, the band gap energy Eg (or emission wavelength) of the MQW structure is changed to the mask width W.
can be varied by m.

If the Eg control by the MOVPE selective growth is used, a connection structure of an optical waveguide structure having different Eg can be manufactured by one crystal growth, and the yield of the semiconductor optical integrated circuit can be improved and the conductivity can be improved. High coupling efficiency between the waveguides can be obtained. FIG. 5 shows an example in which a distributed reflection (DBR) semiconductor laser having a wavelength tunable mechanism is manufactured (see Japanese Patent Application No. 3-067498). FIG. 5C shows a sectional view of the element. First, the (100) -oriented 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 the -InP spacer layer 3 is grown on the entire surface, FIG.
As shown in the top view, a pair of SiO ₂ stripe masks 20 are formed on the surface at a constant interval Wg 1 in the [011] direction. At this time, the mask width is set to Wm 1 in the active region 31,
Wm 1 'in the phase control region 32 and the DBR region 33
(Wm 1> Wm 1 ′). Then, the n-InP cladding layer 4, the MQW active layer 5, and the p-InP cladding layer 6 are formed in the waveguide region 21 sandwiched between the stripe masks 20.
Select to grow.

[0006] Next, as shown in FIG. 5 (b), the opposing side edges of the stripe mask 20 are partially removed to increase the width of the waveguide region to Wg 2, and the p-InP
The clad layer 7 and the p-InGaAs (P) cap layer 8 are selectively grown. When the growth pressure is 76 Torr and 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, EFFC 1992 lecture paper F
B10 (T. Sasaki et al., Op.
physical Fiber Communication
Conference, San Jose, U.S.A. S.
A. , 1992, Paper FB10).

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

FIG. 6 shows an example of a structure of an integrated light source of a distributed feedback (DFB) semiconductor laser and a semiconductor optical modulator, which is described in Electronics Letters, Vol. 27, pp. 2138. (M. Aoki et al., Elec.
tronics Letters, Vol. 27, p
p. 2138, 1991). Here, the MQW structure is formed on the entire surface of the optical modulator region 38 having a large Eg. FIG. 6C shows a cross-sectional view. As a manufacturing method, as shown in a surface view in FIG.
On the n-InP substrate 1 on which the O ₂ stripe mask 20 (width Wm 1, interval Wg 1) and the grating 24 are formed only in the DFB laser region 34, n-InGaAsP is formed.
A guide layer 2, an n-InP spacer layer 3 'MQW active layer 5, and a p-InP cladding layer 6 are grown. Next, FIG.
As shown in the surface view of FIG. 2B, one SiO ₂ stripe mask 22 (width Wa,
Wa <Wg1) is formed, and the substrate 1 is mesa-etched 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 buried 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 is conventionally used.

[0009] In manufacturing a semiconductor optical amplifier which is important in an optical fiber communication system, 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 buried with a semiconductor layer having a large band gap energy. IOC, see 1989 Lecture Paper 20C2-2.
(I. Cha et al., 100C'89, Kob.
e, paper 20C2-2). As a method of forming a window structure using selective growth, a method has been filed in which a mask is formed in a window region so that a waveguide layer is not formed, and then a cladding layer is embedded (Japanese Patent Application No. Hei. 21
No. 6027).

[0010]

The device manufacturing method shown in FIG. 5 uses an MQW without using semiconductor etching.
The feature is that 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 a region having a large Eg, the stripe mask 2
Since the MQW structure is formed by selective growth using 0, the Eg difference obtained is limited as can be seen from FIG. 4C, and when an optical waveguide or the like is integrated in a semiconductor laser, However, there is a problem that Eg 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 has a feature that a relatively large Eg difference can be obtained because the MQW layer 5 is entirely grown in a region having a large Eg. However, the conventional method involves a mesa etching process of a semiconductor, which complicates the process and causes a problem that the device characteristics are likely to vary due to the variation of 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 end portion of the selectively formed waveguide layer is difficult to be smoothly filled.

[0013]

According to a method of manufacturing an optical semiconductor device for solving the above-mentioned problems, at least a part of a semiconductor substrate having a first optical waveguide layer formed on an entire surface thereof is formed at least from a quantum well layer. A second optical waveguide layer is formed in a stripe shape, while being formed on the entire surface in another region without interruption, and further, a semiconductor cladding layer covers the second optical waveguide layer formed in a stripe shape. The optical semiconductor device is characterized in that the optical semiconductor device is formed so as to form a stripe-shaped projection on the second optical waveguide layer formed on the entire surface.

Alternatively, while the layer thickness of the first optical waveguide layer is constant throughout, the layer thickness of the quantum well layer is larger in the stripe-shaped region than in other regions. An optical semiconductor device characterized by the following.

Alternatively, a step of crystal-growing a semiconductor multilayer film including a first optical waveguide layer over the entire surface of a semiconductor substrate, a step of locally forming two opposing first dielectric thin film stripes, and A second optical waveguide layer including a well structure is selectively grown in a growth region inside the first dielectric thin film stripe opposite to the first dielectric thin film stripe, and is entirely grown in a region where the first dielectric thin film stripe is not formed. Performing the step of removing the first dielectric thin film stripe;
The two opposing second dielectric thin film stripes are
Forming the entire surface of the substrate so as to sandwich the second optical waveguide layer formed in the region sandwiched by the dielectric thin film stripes;
In a growth region sandwiched between the second dielectric thin film stripes,
A method for manufacturing an optical semiconductor device, comprising a step of selectively growing a semiconductor multilayer film including a semiconductor cladding layer.

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

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

Alternatively, in the above method for manufacturing an optical semiconductor device, 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 face of the selectively formed ridge structure has a very smooth crystal face, so that there is a feature that when an optical waveguide is manufactured, waveguide loss due to scattering is greatly reduced. 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. FIG.
(B) shows a cross-sectional view. The surface of the InP semiconductor substrate 1 has I
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, interval Wg 2) is formed, and the InP cladding layer 7 is selectively grown in the interposed 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 surface. In the ridge optical waveguide fabricated in this manner, extremely low waveguide loss is obtained.

When a semiconductor optical integrated circuit is manufactured by using the method for manufacturing an optical semiconductor device of the present invention, in the formation of an MQW layer, a stripe mask is not used in a region having a large Eg as in the example of FIG. At the same time as forming the entire surface, other regions having a 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 the waveguide region, as in the example of FIG.
At the same time as forming the ridge waveguide structure by selectively growing the P layer, an InP cladding layer is selectively formed in other regions so as to cover the MQW layer as in the example of FIG. By employing 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 a semiconductor. . In the region where the MQW layer is grown on the entire surface, another layer is previously grown on the entire surface in order to keep the propagation mode in the waveguide stable because the layer thickness of the MQW layer is thin.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 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 tunable DBR laser. FIGS. 1A and 1B are surface views showing the pattern of a stripe mask in the first and second selective growths, respectively. FIGS. 1C and 1D show the active region and the active region after the completion of the crystal growth, respectively. FIG. 3 is a cross-sectional view illustrating a structure of a DBR region. This device is manufactured by three crystal growths.

First, the D of the (100) -oriented n-InP substrate 1
A grating is formed on the BR region 33. Subsequently, an n-InGaAsP guide layer 2 (layer thickness 100 n
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, an interval Wg 1 = 1.5 μm) is formed only in the active region 31 in the [001] direction. Then, the n-InP cladding layer 4 (layer thickness 50 nm, carrier concentration 1 × 10 ¹⁸ c
m ⁻³ ), MQW active layer 5 (consisting of 7 layers of InGaAs well and InGaAsP barrier, with well and barrier thicknesses of 7 nm and 15 nm, respectively), p-InP cladding layer 6 (layer thickness of 200 nm, carrier concentration of 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 in the active region 31, and in the phase control region 32 and the DBR structure 33 grown over the entire surface. Layer thickness is about 1/3
Becomes Once the stripe mask 20 is removed,
As shown in FIG. 1B, a pair of SiO ₂ stripe masks 22 (width Wm 2 = 10 μm, interval Wg 2 = 6 μm) are again formed.
m) is formed in the entire region in the [011] direction such that the waveguide region 21 is at the center. And the p-InP cladding 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. Each of the layer thicknesses is a value in a structure selectively formed in the growth region 23 sandwiched between the stripe masks 22.

By this selective growth, FIGS. 1 (c) and 1 (d)
The p-InP cladding 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 as shown in FIG. That is,
The former has a structure similar to FIG. 5C, and the latter has a structure similar to FIG. 7B. The boundary between the two waveguide regions is formed without interruption. The MQW active layer has a growth pressure of 150 Torr.
r, and as shown in FIG.
The shift amount of the emission peak wavelength due to the mask width is larger than 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 was 1.40 μm. Conventionally, as shown in FIG. 5A, in the DBR region, an MQW structure is selectively formed in a region sandwiched between masks having a width of Wm 1 ′ = 4 μm, and the growth pressure is 76 Torr. The wavelength is 1.
It was 50 μm.

As described above, the wavelength difference can be increased from 50 nm to 150 nm by using the device manufacturing method of the present invention. After completion of the crystal growth in this manner, SiO
_Two films are formed, a window is opened in a stripe shape only on the waveguide region of each region, a p-side electrode is formed in a pattern on the p-InGaAs cap layer, and an n-side electrode is formed on the n-InP substrate. Was formed. Active region 31, phase control region 32
And DBR region 33 have a length of 600 μm, 1
50 μm and 300 μm.

As a result of evaluating the characteristics of the prototype 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 with mode jumps while maintaining the optical output at 10 mW. Further, by injecting a current up to 10 mA into the phase control region, it was possible to cover the entire wavelength region where the mode jump occurred. In the conventional structure formed by selective growth (FIG. 5), since the wavelength difference between the active region and the phase control region was not sufficient, even if current was injected into the phase control region, it could not be completely covered.

Since the wavelength difference can be increased by the present invention, a conventional three-electrode wavelength-tunable DBR laser, for example, see Electronics Letters, vol. 23, p. 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), high yield and uniformity, which are features of the manufacturing method without using mesa etching of a semiconductor, could be maintained. Second
An example will be described. FIG. 2A shows a DFB laser,
FIG. 11 is a front view showing a mask pattern of an element in which a semiconductor optical amplifier and an optical waveguide are integrated when an MQW structure is grown. FIG.
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 that of the example of FIG. 1, and the grating is formed only in the DFB region 34. As a result of the device characteristic evaluation, an internal gain of the semiconductor optical amplifier was 20 dB, and a waveguide loss in the optical waveguide was 15 cm ⁻¹ . The coupling efficiency at the coupling section between the optical amplifier and the optical waveguide is 95.
% Value was estimated.

As an embodiment of the semiconductor optical amplifier of the present invention, a low end face reflectivity is realized without increasing the loss in the window region by growing the entire waveguide layer in the window region.
Specifically, as shown in the top view of FIG. 2B, an SiO ₂ stripe mask 20 is formed only in the active region 31 and M
A waveguide layer having a QW structure is selectively formed in the waveguide region 21, and grows over the entire surface of the window region 37. Next, FIG.
(C) As shown in the surface view, 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 was made wider in the window region 37 than in the active region 31 to reduce the internal loss in the window region. Active region length 300μ
m and a window region length of 30 μm each, an internal gain of 25
A dB and an end face reflectivity of 10 ⁻⁵ were realized.

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

Next, as shown in FIG.
An iO ₂ stripe mask 20 is formed in the active region 31, the optical modulator region 38, and the optical amplifier region 35 in the [011] direction. 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 of. The width of the waveguide region 21 in each region was fixed at 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 cladding layer 4 (layer thickness 5
0 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), MQW active layer 5 (seven layers of InGaAs well and InGaAsP
A barrier was formed, and the well thickness and the barrier thickness were 7 nm and 15 nm, respectively, and the p-InP clad layer 6 (layer thickness 2
It is grown to a thickness of 00 nm and a carrier concentration of 7 × 10 ¹⁷ cm ⁻³ ). The above layer thickness is the same as that of the mask stripe 2 of the active region 31.
This is a value in a structure selectively formed in the waveguide region 21 sandwiched between 0.

After the mask stripe 20 is once removed, as shown in the surface view of FIG.
O ₂ mask stripe 22 (width 10 μm, interval 6 μm)
Is formed over the entire region such that the waveguide region 21 is 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 between the masks is It is constant at 6 μm in the entire region.
Then, the p-InP cladding layer 7 (layer thickness 1.5 μm, carrier concentration 7 × 10 ¹⁷ cm ⁻³ ) and the p-InGaAs cap layer 8 (layer thickness 300 nm, carrier concentration 1 × 10 ¹⁹ cm ³ )
^-3 ) to grow. Each layer thickness is a value in a structure selectively formed in the growth region 23.

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

A pattern electrode was formed in each of 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 optical amplifier side end face. An extinction ratio of 15 dB when a voltage having an amplitude of 2 V is applied to the optical modulator.
Was obtained, and a good modulated optical waveform was obtained in the modulation of 2.5 Gb / s. The threshold current and light output of 10 continuous elements are 8 to 15 mA and 18 to 2 mA, respectively.
It was 8 mW, and the uniformity was good.

Hereinafter, the present invention will be described in more detail with reference to the drawings showing 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 are integrated according to an embodiment of the present invention. . The wavelength tunable 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
At 3, the light is guided to a star coupler 44, which is a multiplexer, and is further collectively amplified by an optical amplifier 45. In order to realize such an element, the following may be performed. That is, the insulating film masks 47 and 48 are formed partially on the semiconductor substrate 46 on which the diffraction grating is partially formed, where the wavelength tunable laser 41 and the optical amplifier 45 are formed. The diffraction grating is formed only in the DBR region 49. The portion where the active region 50 is formed has a wide mask width, and the portion where the DBR region 49 is formed has a narrow mask width. Mask width is 15 μm and 8 μm respectively
And The wavelength composition of the MQW structure is 1.55 μm, 1.48 μm,
1.40 μm. It was confirmed that the composition at the flat portion was sufficiently transparent for the laser oscillation wavelength of 1.55 μm. The mask interval is 1.5 μm, and a buried MQW waveguide layer can be automatically formed there. The length of the mask is 400 μm for each of the active region and the DBR region.
The thickness was 200 μm. In the portion of the optical amplifier 45, the width, length, and interval of the mask are 15 μm and 600 μm, respectively.
It was 1.5 μm. The substrate 4 on which the mask is formed as described above
6, InGaAs, InGaAsP (wavelength composition 1.2)
μm) was grown. The film thickness was set to be 60 A in the flat portion. The area between the masks 47 and 48 was 2 mm in length. At this stage, the MQW waveguide is formed in the region between the masks so as to be included in the mesa structure, while the region without the mask is formed flat. A mask is again formed on the whole of the semiconductor structure obtained in this manner, a part of the mask which becomes the wavelength tunable LD 41 and the optical amplifier 45 is partially removed, and a cladding layer 51 is formed so as to cover the mesa structure. At this time, portions constituting the MZ optical modulator 42, the waveguide 43, and the star coupler 44 are patterned as shown in the figure, and the ridge 14 is formed simultaneously with the cladding layer 12. The width of the cladding layer is 6 μm,
The width of the ridge 14 was 4 μm at the bottom. This gives D
The cross section of the BR-LD or optical amplifier is shown in FIG.
In the embedded structure as shown in FIG.
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 had 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 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 can transmit an optical signal at a high speed of 10 Gb / s, for example, with a wavelength interval of 4 nm, and is very useful as a high-speed light source for wavelength-division multiplexed optical communication.

FIG. 9 is a view showing a process of manufacturing an integrated element of a wavelength tunable laser and an optical switch according to 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 at the portion where the mask is formed and the wavelength composition of the MQW layer at the flat portion are 1.55 μm, respectively.
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 to be the optical switch 63 was 2 mm long. 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 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 a 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 portion, the width of the ridge waveguide was 4 μm. A desired optical integrated device was obtained by partially forming electrodes and further forming a heating resistance wire of Pt on the DFB-LD to obtain a resistance heating type variable wavelength DFB-LD.

By controlling the current flowing through the Pt resistor to about several tens mA with such an element, a wavelength tunable operation in a range of about 4 nm can be obtained. Actually, a tunable DFB-LD having two wavelengths was formed. Resistance heating type DFB-
In the LD, the switching time for wavelength switching is several milliseconds, and these are set in advance at frequency intervals of several tens of GHz, and a voltage is applied to the optical switch so that 1
Switching can be performed in a switching time of about ns.

As described above, according to the present invention, the selective MOVPE
By skillfully applying the growth technology, it is possible to form a buried waveguide and a ridge-structured waveguide at the same time. An integrated device can be realized.

In the embodiment of the present invention, a two-electrode DBR-LD or a resistance heating type DFB-LD is shown as a variable wavelength light source.
There is no problem using elements having various structures such as an LD, a three-electrode DBR-LD, a vertical coupling filter type wavelength variable LD, and a composite resonator type wavelength variable LD. Further, a directional coupler type optical switch has been described, but the present invention is not limited to this. The material system used is of course 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 a high yield. Also, by using the method for manufacturing an optical semiconductor device of the present invention, MOVPE
In a semiconductor optical integrated circuit manufactured by selective growth,
It has become possible to manufacture a device by increasing the shift amount of the band gap energy of the MQW structure without using a mesa etching process of a semiconductor as compared with the related art. By using the present invention, the characteristics of a DBR semiconductor laser can be improved as compared with a device using conventional selective growth.
The present invention was also applied to the manufacture of various semiconductor optical integrated circuits having a structure in which a semiconductor laser, a semiconductor optical modulator, and a semiconductor optical amplifier such as a semiconductor optical amplifier were integrated using an optical waveguide, and a semiconductor optical amplifier having a window structure. In this way, it is possible to achieve both good device characteristics and high uniformity by manufacturing a semiconductor optical integrated circuit, which has conventionally been a complicated manufacturing method, by a simple method.

[Brief description of the drawings]

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

FIG. 2 is an embodiment of a method of manufacturing a distributed feedback semiconductor laser, an integrated device of a semiconductor optical amplifier and an optical waveguide, and a semiconductor optical amplifier with a window structure according to the first, second, third, fourth and fifth aspects of the present invention; FIG.

FIG. 3 is a front view showing an embodiment of a method of manufacturing a semiconductor optical integrated circuit according to the first, second, third, fourth and sixth aspects of the present invention.

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

5A and 5B are a front view and a cross-sectional view illustrating a method of manufacturing a distributed reflection semiconductor laser according to a conventional invention.

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

7A and 7B are a front view and a cross-sectional view illustrating a method for manufacturing a ridge-type optical waveguide according to a conventional invention.

FIG. 8 shows a wavelength tunable laser and a Mach-Zehnder optical modulator,
FIG. 3 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 element of a wavelength tunable laser and an optical switch.

[Explanation of symbols]

Reference Signs List 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 blocking layer 10 n-InP blocking layer 20 SiO ₂ stripe masks 21 waveguiding regions 22 SiO ₂ stripe masks 23 growth region 24 grating 31 active region 32 the phase control region 33 DBR region 34 DFB region 35 the semiconductor optical amplifier region 36 waveguide Area 37 Window area 38 Semiconductor optical modulator area 41 Wavelength tunable DFB-LD 42 MZ optical modulator 43 Waveguide 44 Star coupler 45 Optical amplifier 46 Substrate 47 Mask 48 Mask 49 DFB area 50 Active area 51 Cladding layer 52 Ridge 61 Mask 6 2 DFB-LD 63 Optical switch

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-100291 (JP, A) JP-A-4-105383 (JP, A) JP-A-4-243216 (JP, A) JP-A-4- 303982 (JP, A) JP-A-5-82909 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (6)

(57) [Claims] 1. A semiconductor substrate having a first optical waveguide layer formed on the entire surface thereof. In a certain region, a second optical waveguide layer comprising at least a quantum well layer is formed in a stripe shape on the first optical waveguide layer. ,
In another region subsequent to this region, the second optical waveguide layer is formed on the entire surface of the first optical waveguide layer, and in the certain region, the second optical waveguide layer is formed by forming a semiconductor cladding layer in a stripe shape. Wherein the semiconductor cladding layer is formed on the second optical waveguide layer so as to form a stripe-shaped projection in the another region. 2. The optical semiconductor device according to claim 1, wherein:
While the thickness of the optical waveguide layer is constant throughout,
An optical semiconductor device, wherein the thickness of a quantum well layer 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, a step of locally forming two opposing first dielectric thin film stripes, and The second optical waveguide layer including a well structure is formed by the first optical waveguide layer.
A step of selectively growing in a growth region on the inside of the dielectric thin film stripe opposite thereto and growing the entire surface in a region where the first dielectric thin film stripe is not formed; and removing the first dielectric thin film stripe. And forming two opposing second dielectric thin film stripes into the first dielectric thin film stripe.
Forming the entire surface of the substrate so as to sandwich the second optical waveguide layer formed in the region sandwiched by the dielectric thin film stripes;
Selectively growing a semiconductor multilayer film including a semiconductor cladding layer. 4. The method of manufacturing an optical semiconductor device according to claim 3, wherein a stripe width of said first dielectric thin film stripe or said second dielectric thin film stripe is changed in a stripe direction. Manufacturing method. 5. The method of manufacturing an optical semiconductor device according to claim 3, wherein a width of a growth region sandwiched between the first dielectric thin film stripe and the second dielectric thin film stripe is changed in a stripe direction. Manufacturing method of an optical semiconductor device. 6. The method of manufacturing an optical semiconductor device according to claim 3, wherein said second dielectric thin film stripe is formed in a curved shape in a part of said optical waveguide region. .