JP2003332679A - Semiconductor laser and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser which is stable in element characteristics and superior in reliability. <P>SOLUTION: The semiconductor layer is equipped with: a first conductivity- type InP substrate; a first conductivity-type InP buffer layer and an active layer successively formed on the first conductivity-type InP substrate; a diffraction grating which is composed of a second conductivity-type InP barrier layer, a second conductivity-type InGaAs diffraction grating layer, and a second conductivity-type InP cap layer which are successively formed on the active layer and is continuously repeated at prescribed cycles along an optical waveguide direction; and a second conductivity-type first InP clad layer, a second conductivity-type second InP clad layer, and a second conductivity-type InP contact layer which are successively formed on the main surface of the substrate containing the diffraction grating. The side of the diffraction grating forms an angle of 70° to below 90° with the main surface of the wafer in the optical waveguide direction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a method for manufacturing the same, and more specifically, it is possible to control the coupling constant to a desired value with good reproducibility, resulting in stable device characteristics and deterioration of the device. It is intended to provide a semiconductor laser having a diffraction grating that is difficult to perform and has high reliability, and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 7 shows a method of manufacturing a conventional distributed feedback (hereinafter referred to as DFB) semiconductor laser provided with a diffraction grating disclosed in Japanese Patent Laid-Open No. 164380/60.
Hereinafter, a conventional DFB having a diffraction grating will be described with reference to FIG.
A method for manufacturing the semiconductor laser will be described. In the figure, 17 is n
Type InP substrate, 18 n-type InP buffer layer, 19 undoped In _0.72 Ga _0.28 As _0.61 P
_0.39 active layer, 20 is p-type In _0.85 Ga _0.15
As _0.33 P _0.67 Light guide layer, 21 is p-type InP
A cap layer and 22 are p-type InP clad layers, respectively.

First, by the epitaxial crystal growth method,
The n-type InP buffer layer 18 is formed on the n-type InP substrate 17 by 5
μm, undoped In_0.72Ga_0.28As
_0.61P _0.390.1 μm active layer 19 with p-type In
_0.85Ga_0.15As_0.33P_0.67Light guide
Layer 20 is 0.15 μm, p-type I with high meltback resistance
Crystal growth of the nP cap layer 21 is sequentially performed by 0.05 μm.
It

Lithography and etching techniques are applied to the wafer after crystal growth to completely penetrate the p-type InP cap layer 21 and the bottom part thereof is p-type In _0.85 Ga.
_{0.1 5} As _0.33 P _{0.67 The} diffraction grating 12 reaching the light guide layer 20 is formed. 2 on this diffraction grating 12
The epitaxial crystal growth for the second time, that is, recrystallization growth is performed, and the p-type InP cladding layer 22 is crystal-grown to a thickness of about 1 μm to obtain a double heterostructure wafer having a diffraction grating 12 for a DFB semiconductor laser. Note that p-type In
The P clad layer 22 is grown at a crystal growth temperature of 550 ° C. Mesa etching and buried crystal growth are further performed on the double heterostructure wafer after epitaxial crystal growth, both sides are cleaved, end face reflection films are formed on both end faces (not shown), and single mode operation is performed. A DFB type semiconductor laser was obtained.

In the conventional method of manufacturing a DFB semiconductor laser having such a diffraction grating, liquid phase crystal growth (LPE), which is a kind of epitaxial crystal growth, is formed on the diffraction grating 12.
Method) p-type I having high resistance to meltback
Since the nP cap layer 21 is formed, the diffraction grating 1
The meltback of No. 2, that is, the problem that the underlying crystal growth layer is melted in the liquid phase during the recrystallization growth in the liquid phase crystal growth method can be minimized. As a result, the depth of the diffraction grating 12 was preserved, and a very important coupling constant in the DFB semiconductor laser could be maintained at a large value. Here, the coupling constant refers to the degree to which light propagating in the optical waveguide in opposite directions is diffracted by the diffraction grating and is coupled per unit length. Generally, as the depth of the diffraction grating increases, the coupling constant increases. Will also grow.

Further, FIG. 8 shows another conventional D having the diffraction grating disclosed in Japanese Patent Laid-Open No. 10-22558.
3 shows a method for manufacturing an FB type semiconductor laser. In the figure, 21 is a p-type InP cap layer, 22 is a p-type InP clad layer, 23 is an n-type InGaAsP guide layer, 24 is an InGaAsP active layer, 25 is a p-type InGaAsP guide layer, 26 is a p-type InP layer, and 27 is p-type InGaAsP
Diffraction grating layer, 28 is p-type InGaAsP contact layer,
Are shown respectively.

A method of manufacturing a DFB semiconductor laser according to another conventional technique will be described below. An n-type InGaAsP guide layer 23, an InGaAsP active layer 24, and a p-type InGaAsP guide layer 25 are sequentially epitaxially grown on the n-type InP substrate 17 (FIG. 8A). After forming the optical confinement / current block structure (not shown), p-type InP
Layer 26, p-type InGaAsP diffraction grating layer 27, p-type In
The P cap layer 21 is sequentially epitaxially grown (FIG. 8B).

The diffraction grating 12 is formed by using an interference exposure technique (photolithography technique), an etching technique or the like (FIG. 8C). The etching bottom reaches the p-type InP layer 26 from the surface of the p-type InP cap layer 21 through the InGaAsP diffraction grating layer 27.
It is located at a position that does not reach the AsP guide layer 25. The p-type InP clad layer 22 is epitaxially grown on the diffraction grating 12 to embed the diffraction grating 12. Note that the crystal growth temperature during epitaxial crystal growth of the p-type InP clad layer 22 is not described. Further on the p-type InP clad layer 22, p-type InGaAsP
The contact layer 28 is epitaxially grown (FIG. 8).
(D)) A DFB semiconductor laser is obtained by forming electrodes on the upper and lower wafer main surfaces and forming an optical resonator by cleavage (not shown).

In such another conventional DFB type semiconductor laser, when the crystal of the p-type InP cladding layer 22 is grown, the portion of the p-type InP that is deformed by the influence of heating of the wafer at the crystal growth temperature is deformed. The shape of the InGaAsP diffraction grating layer 27, which was suppressed only by the cap layer 21 and was provided to function as a diffraction grating, did not occur. This is because the InGaAsP diffraction grating layer 27 is protected by the p-type InP cap layer 21 formed thereon. As a result, the controllability of the depth of the diffraction grating was improved, and the coupling constant strongly dependent on the depth of the diffraction grating could be easily controlled.

[0010]

In the DFB semiconductor laser, the coupling between the light wave and the diffraction grating is the most important parameter, and in order to stabilize the device characteristics such as single mode property and temperature characteristic, the coupling constant is Creating the desired value is of paramount importance. However, the above-mentioned prior art only points out the importance of controlling the depth of the manufactured diffraction grating, and the side angle, which is one of the important factors in the shape of the diffraction grating, that is, the diffraction grating in the optical waveguide direction. No mention was made of the angle between the side surface and the main surface of the wafer.

Further, in the conventional method of manufacturing a DFB type semiconductor laser, it is difficult to control the side surface angle of the diffraction grating. Therefore, in the conventional DFB type semiconductor laser, the periodicity variation of the diffraction grating, which is inevitable in manufacturing, that is, the controllability of the coupling constant is deteriorated due to the variation of the bottom width of the diffraction grating between the individual diffraction gratings. As a result, there is a problem that the device characteristics are not stable. Furthermore, since the deformation prevention layer for the diffraction grating is inserted on the diffraction grating, the step becomes large during the burying growth, and a large number of crystal defects occur in the buried layer due to the effect of the step, and the reliability of the device deteriorates. There was also a defect.

In the semiconductor laser and the method for manufacturing the same according to the present invention, by controlling the side surface angle of the diffraction grating to a predetermined angle, the controllability of the coupling constant with respect to the periodic variation of the width of the bottom of the diffraction grating is improved, As a result, the objective is to obtain a semiconductor laser with stable device characteristics.

Another object of the present invention is to provide a semiconductor laser and a method of manufacturing the same, which provides a highly reliable semiconductor laser in which crystal defects in the buried layer are reduced.

[0014]

A semiconductor laser according to the present invention includes a first conductivity type InP substrate and the first conductivity type IP substrate.
A first conductivity type InP buffer layer formed on an nP substrate, an active layer formed on the first conductivity type InP buffer layer, and a second conductivity type InP sequentially formed on the active layer. A diffraction grating which is composed of a barrier layer, a second conductivity type InGaAsP diffraction grating layer, and a second conductivity type InP cap layer, and which is continuously repeated at a predetermined cycle along the optical waveguide direction; A first conductivity type InP clad layer, a second conductivity type second InP clad layer, and a second conductivity type InP contact layer that are sequentially formed on the main surface of the wafer including the diffraction grating. The angle formed between the side surface of the diffraction grating and the main surface of the wafer is 70 degrees or more and less than 90 degrees.

Also, in the semiconductor laser according to the present invention, the layer thickness of the second conductivity type first InP cladding layer is 0.025.
It was set to be not less than μm and not more than 0.1 μm.

A method of manufacturing a semiconductor laser according to the present invention is
A step of forming a diffraction grating on the main surface of the wafer; a step of epitaxially growing a first semiconductor layer on the main surface of the wafer including the diffraction grating at a crystal growth temperature TG1; and a crystal growth on the first semiconductor layer. A step of epitaxially growing the second semiconductor layer at a temperature TG2, wherein the crystal growth temperature TG1 is higher than the crystal growth temperature TG2 by 50.
The temperature was set at a low temperature of 70 ° C.

Further, in the method for manufacturing a semiconductor laser according to the present invention, after the step of epitaxially growing the second semiconductor layer, the angle between the side surface of the diffraction grating and the main surface of the wafer in the optical waveguide direction is 70 degrees or more. The angle is less than 90 degrees.

In the method of manufacturing a semiconductor laser according to the present invention, the first conductivity type InP substrate is formed on the first conductivity type InP substrate.
P buffer layer, active layer, second conductivity type InP barrier layer,
A step of sequentially epitaxially growing each layer of the second conductivity type InGaAsP diffraction grating layer and the second conductivity type InP cap layer, and the second conductivity type InP barrier layer and the second conductivity by a lithography technique and a dry etching technique. Type InGaAsP diffraction grating layer and the second conductivity type InP cap layer, forming a diffraction grating continuously repeated at a predetermined period along the optical waveguide direction, and a wafer main surface including the diffraction grating A step of epitaxially growing a second conductivity type first InP clad layer thereon, and a second conductivity type second InP clad layer and a second conductivity type InP on the second conductivity type first InP clad layer.
A step of sequentially performing epitaxial crystal growth on the contact layer, and a crystal growth temperature T when epitaxially growing the second conductivity type first InP clad layer.
G1 is 5 from the crystal growth temperature TG2 at the time of epitaxial crystal growth of the second conductivity type second InP clad layer.
The temperature was set to a low temperature of 0 to 70 ° C.

In the method of manufacturing a semiconductor laser according to the present invention, the first conductivity type InP substrate is formed on the first conductivity type InP substrate.
P buffer layer, active layer, second conductivity type InP barrier layer,
A step of sequentially epitaxially growing each layer of the second conductivity type InGaAsP diffraction grating layer and the second conductivity type InP cap layer, and the second conductivity type InP barrier layer and the second conductivity by a lithography technique and a dry etching technique. Type InGaAsP diffraction grating layer and the second conductivity type InP cap layer, a step of forming a diffraction grating that is continuously repeated at a predetermined period along the optical waveguide direction, and a mass transport by heat treatment. A step of melting the second conductivity type InP cap layer to form a second conductivity type first InP clad layer covering the main surface of the wafer including the diffraction grating; and a step of forming a second conductivity type first InP clad layer on the second conductivity type first InP clad layer. A step of sequentially epitaxially growing a second conductivity type second InP cladding layer and a second conductivity type InP contact layer; Comprise becomes, the heat treatment temperature TG at the time of heat treatment of the InP cap layer of the second conductivity type
3 is 50 from the crystal growth temperature TG2 when epitaxially growing the second conductivity type second InP clad layer.
The temperature was set at a low temperature of 70 ° C.

In the method of manufacturing a semiconductor laser according to the present invention, the second conductivity type InP cap layer is formed by 0.15 μm.
It was set to m or more and 0.3 μm or less.

In the method of manufacturing a semiconductor laser according to the present invention, the crystal growth temperature TG2 is set in the range of 540 to 580 ° C.

Further, in the method of manufacturing a semiconductor laser according to the present invention, after the step of sequentially epitaxially growing the second conductivity type second InP cladding layer and the second conductivity type InP contact layer, the above-mentioned method in the optical waveguide direction is adopted. The angle formed between the side surface of the diffraction grating and the main surface of the wafer was 70 degrees or more and less than 90 degrees.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. A method of manufacturing a semiconductor laser according to the first embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is a method for manufacturing a semiconductor laser according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a configuration of an MQW active layer in the semiconductor laser according to the first embodiment,
FIG. 3 is a sectional view of a part of the diffraction grating in the semiconductor laser of the first embodiment.

The semiconductor laser of the first embodiment will be described below.
The manufacturing method of the z will be described. In the figure, 1 is a p-type InP substrate,
2 is a p-type InP buffer layer, 3 is a multiple quantum well active layer
(MQW active layer) 4, n-type InP barrier layer, 5 n-type
In_0.8Ga_0.2As_{0. Four}P_0.6Diffraction grating layer,
6 is an n-type InP cap layer, and 7 is an n-type first InP cladding layer.
Layer (first semiconductor layer), 8 is n-type second InP clad
Layer (second semiconductor layer), 10 is n-electrode, 11 is p-electrode,
12 is a diffraction grating, 13 is a side angle of the diffraction grating, and 14 is I
n_0.8Ga_0.2As_0.9P_0.1Well layer, 15
Is In_0.7Ga _0.3As_0.6P_0.4Barrier layer,
Are shown respectively.

First, a p-type InP substrate 1 is formed on the p-type InP substrate 1.
The buffer layer 2 is laminated to a thickness of 2 μm and then shown in the sectional view of FIG.
With a thickness of 0.01 μm_0.7Ga_0.3As
_{0. 6}P_0.4Barrier layer 15 and 0.01 μm thick In
_0.8Ga_0.2As_0.9P _0.19 well layers 14
Multi-quantum well active layer (MQW active layer) 3 stacked
Layer. Furthermore, the n-type InP barrier layer 4 is 0.3 μm,
n-type In_0.8Ga_{0. Two}As_0.4P_0.6Diffraction grating
The layer 5 is 0.05 μm, and the n-type InP cap layer 6 is 0.0
Layers of 5 μm are sequentially laminated (FIG. 1A). Where epita
The axial crystal growth method includes a metal organic chemical vapor deposition method,
The so-called MOCVD (Metal Organic Chemical Vapor De
position) method is used.

After the above epitaxial crystal growth, an electron beam
Lithography technology such as exposure and dry etching technology
Using a diffraction pattern that is continuous in a predetermined period along the optical waveguide direction.
Form the child 12. In this case, the etching depth is n-type I.
nP cap layer 6, n-type In _0.8Ga_0.2As
_0.4P_0.6N-type InP barrier layer through the diffraction grating layer 5
Try to reach midway through 4. In addition, n-type In
_0.8Ga_0.2As_0.4P _0.6The diffraction grating layer 5
It is easy to use ly etching to etch in a substantially vertical direction.
Therefore, the etching angle of the diffraction grating 12, that is, diffraction
The side surface angle 13 (FIG. 3) of the grating is 80 with respect to the main surface of the wafer.
The range is 70 degrees or more and less than 90 degrees centering on the degree. By the way
The main surface of the wafer is parallel to the surface of the p-type InP substrate 1.
Means a face. After forming the diffraction grating 12, the diffraction grating 12 is included.
The n-type first InP clad layer 7 (first
(Semiconductor layer) with a crystal growth of 0.05 μm, and the n-type second
0.5 μm product of InP clad layer 8 (second semiconductor layer)
Layer.

At this time, the crystal growth temperature TG1 of the n-type first InP clad layer 7 is 500 ° C., and the crystal growth temperature TG2 of the n-type second InP clad layer 8 is 560 ° C. That is, the crystal growth temperature TG2 is intentionally set to a high temperature of about 60 ° C. with respect to the crystal growth temperature TG1. At this time, the n-type first InP cladding layer 7 has a relatively low temperature (TG
Since the crystal is grown at the crystal growth temperature of 500 ° C., which is 1), the deformation of the shape of the diffraction grating 12 due to the influence of heat is n-type I.
The n-type InP cap layer 6 occurs only in the nP cap layer 6.
The etching shape of the lower n-type In _0.8 Ga _0.2 As _0.4 P _0.6 diffraction grating layer 5 is not deformed. That is, the side surface angle 13 of the diffraction grating 12 has almost the same value as immediately after etching. This is n-type In _0.8 Ga _0.2 As
_0.4 P _{0 . This} is because the upper part of the _6- diffraction grating layer 5 is covered and protected by the n-type InP cap layer 6. further,
The growth film thickness of the n-type first InP cladding layer 7 is 0.05 μm.
Since it is extremely thin, crystal defects do not occur at the step portion of the diffraction grating. In addition, this step portion is
It indicates a total of four places, the edge part at the bottom part and the edge part at the top part of the trapezoidal diffraction grating. Crystal growth temperature TG1,
That is, n-type first epitaxially grown at 500 ° C
In the InP clad layer 7, when the film thickness is 0.05 μm,
No crystal defect was observed by transmission electron microscopy. This has a crystal defect density of 3 × 10 ¹⁷ cm
^-2 or less is suggested. On the other hand, film thickness 0.2
In the case of μm, the observed crystal defect density is 3 × 10 ¹⁹
cm ⁻² , which adversely affects device characteristics, especially reliability. From this observation result, it was found that the film thickness of the n-type first InP clad layer 7 strongly influences the crystal defect density.

The above-mentioned crystal growth temperature is measured by a method of measuring the temperature of the susceptor on which the p-type InP substrate 1 is mounted in the MOCVD crystal growth apparatus by a thermocouple or a method of directly measuring the susceptor by a pyrometer.

Next, in the crystal growth of the n-type second InP cladding layer 8, the crystal growth temperature TG2 is relatively high 56.
Although the temperature is set to 0 ° C., the diffraction grating 12 is already entirely covered with the n-type first InP cladding layer 7, so that no shape change occurs, and the side surface angle 13 of the diffraction grating immediately after etching can be favorably maintained. Further, since the crystal growth temperature TG2 is high enough to cause surface diffusion, there is an effect that crystal defects at the step portion of the diffraction grating 12 hardly occur.

After that, mesa etching for the purpose of forming an optical waveguide is performed, then a current block structure (not shown) for the purpose of current confinement is crystal-grown, and n-type In is further added.
After the P contact layer 9 is laminated to a thickness of 1 μm to complete the epitaxial crystal growth, the n electrode 1 is formed on the wafer surface side.
0, the p-electrode 11 is formed on the back surface of the wafer by a method such as a vacuum evaporation method or a sputtering method, and the wafer process is completed. In the assembly process, both end faces of the device are formed by cleavage, end face reflection films are formed on the front and rear end faces thereof, and chip separation is performed to obtain a semiconductor laser that operates in a single mode.

In the semiconductor laser of the first embodiment thus obtained, the shape of the diffraction grating 12 is maintained as it is, and the side surface angle 13 of the diffraction grating after completion of the element is 13
Is about 80 degrees just after etching, the n-type first InP cladding layer 7 with the diffraction grating embedded, and the n-type second
It was confirmed by transmission electron microscope observation that almost no crystal defects were generated in the InP clad layer 8.

FIG. 4 shows the diffraction grating width / period (hereinafter referred to as duty).
This is the result of calculation of the variation of the coupling constant with respect to (when referred to as) when the side surface angle 13 of the diffraction grating 12 is 40 degrees and 80 degrees. The diffraction grating width is defined by the bottom of the diffraction grating 12. The coupling constant draws a sine curve with respect to duty. As the side surface angle 13 of the diffraction grating 12 becomes smaller, the peak value of the sine curve moves toward the larger duty. Since the diffraction grating period is about 0.2 μm, the processing width is 0.1 μm or less in order to form the diffraction grating 12 having a duty of 50% or more, which makes the processing itself difficult. Therefore, the duty is generally designed to be around 50%, but variations in the duty always occur in the wafer process during manufacturing.

The variation width of the coupling constant when the duty variation is 50 ± 10% is obtained by setting the side surface angle 13 of the diffraction grating to 4
The results calculated for 0 and 80 degrees are shown in FIG. It can be seen that the variation of the coupling constant with respect to the same duty variation is reduced to less than half of the case where the side surface angle 13 of the diffraction grating is 80 degrees as compared with the case where the side surface angle is 40 degrees. In the semiconductor laser according to the first embodiment of the present invention, the side angle 13 of the diffraction grating is set to 7
Since 0 degree or more and less than 90 degrees, preferably 75 degrees or more and 85 degrees or less and the center value thereof is set to about 80 degrees, it is possible to reduce the variation in duty that is unavoidable in the manufacturing process. The effect of improving the controllability of the coupling constant and stabilizing the device characteristics is obtained.

Further, in the manufacturing process of a semiconductor laser, stress is generally applied to the element after the completion of the manufacturing process, such as cleavage and soldering to a heat dissipation block. When a large number of crystal defects are present in the n-type first InP clad layer 7 and the n-type second InP clad layer 8 which are buried layers, the crystal defects cause a sliding motion due to stress and extend until reaching the MQW active layer 3. If a crystal defect is present in the MQW active layer 3, it becomes a non-radiative recombination center, so that device deterioration is induced during energization. In the semiconductor laser of the first embodiment, as described above, the n-type first InP cladding layer 7 and the n-type second In
Since almost no crystal defects occur in the P clad layer 8, the element deterioration is suppressed and the element reliability is improved.

In the method of manufacturing the semiconductor laser described above, as an example, the crystal growth temperature TG of the n-type first InP cladding layer 7 is used.
1 was 500 ° C., and the crystal growth temperature TG2 of the n-type second InP clad layer 8 was 560 ° C., but the crystal growth temperature TG2 is 540 ° C. or higher and 580 ° C. or lower, and the temperature difference between the crystal growth temperature TG2 and the crystal growth temperature TG1. Is 50 to 70 ° C,
The same effect can be obtained.

In the method of manufacturing the semiconductor laser described above, the layer thickness of the n-type first InP clad layer (first semiconductor layer) 7 is 0.05 μm as an example.
Similar effects can be obtained if the thickness is 25 μm or more and 0.1 μm or less.

Further, in the above-described semiconductor laser manufacturing method, the case where the MOCVD method is applied as the epitaxial crystal growth method is shown, but the same effect can be obtained by another epitaxial crystal growth method (for example, MBE method). Needless to say.

As described above, according to the semiconductor laser and the method of manufacturing the same in the first embodiment, the n-type first In is formed on the diffraction grating layer.
Since the P clad layer is formed and the crystal growth temperature TG1 of the n-type first InP clad layer is set to be relatively lower than the crystal growth temperature TG2 of the n-type second InP clad layer, the shape of the diffraction grating is maintained and a step is formed. Almost no crystal defects are generated in the portion, so that variation of the coupling constant is suppressed against the duty variation that is unavoidable in the manufacturing process. As a result, the controllability of the coupling constant is improved, the element characteristics are stabilized, and the element is degraded. Is suppressed and the reliability of the device is improved.

Embodiment 2. FIG. 6 is a diagram showing a method of manufacturing a semiconductor laser according to the second embodiment of the present invention. In the figure, 16 is an n formed by mass transport.
The first InP clad layer.

First, a p-type InP buffer layer 2 is laminated on the p-type InP substrate 1 to a thickness of 2 μm, and an In layer having a thickness of 0.01 μm is formed.
_0.7 Ga _0.3 As _0.6 P _0.4 barrier layer 15 and 0.01 μm thick In _0.8 Ga _0.2 As _0.9 P
A multiple quantum well active layer (MQW active layer) 3 in which ten _0.1 well layers 14 are stacked is stacked. After that, n-type InP
The barrier layer 4 has a thickness of 0.3 μm and n-type In _0.8 Ga _0.2.
The As _0.4 P _0.6 diffraction grating layer 5 and the n-type InP cap layer 6 are laminated in a thickness of 0.05 μm and 0.2 μm, respectively (FIG. 6).
(A)). Here, the epitaxial crystal growth method is a metal organic chemical vapor deposition method, so-called MOCVD (Metal Oxygen).
rganic Chemical Vapor Deposition) method is used.

Next, the diffraction grating 12 which is continuous in a predetermined cycle along the optical waveguide direction is formed by using a lithography technique such as electron beam exposure and a dry etching technique (FIG. 6).
(B)). In this case, the etching depth is n-type InP cap layer 6, n-type In _0.8 Ga _{0 . 2} As _0.4 P
_0.6 through the diffraction grating layer 5 to reach the middle of the n-type InP barrier layer 4. In addition, n-type In _0.8 Ga
The dry etching of the _0.2 As _0.4 P _0.6 diffraction grating layer 5 can be easily performed with the side surface angle 13 within the range of 70 degrees or more and less than 90 degrees. The side surface angle 13 of the diffraction grating 12 is typically about 80 degrees.

After the diffraction grating 12 is formed and before the crystal growth of the n-type second InP cladding layer 8, the heat treatment temperature (TG3).
By performing heat treatment at 500 ° C. for 5 minutes, n-type In
The P cap layer 6 has an n-type first In region partially having a region moved to the groove portion between the diffraction gratings as a result of the constituent elements thereof being diffused and melted on the wafer surface by mass transport.
It becomes the P clad layer 16 (FIG. 6C). In such a mass transport, the shape changes so that the convex portion on the crystal plane becomes round. However, in the method of manufacturing the semiconductor laser according to the second embodiment, the n-type InP cap layer 6 is formed.
Is formed as thick as 0.2 μm, the diffraction grating 12 is formed by a change in shape due to mass transport.
Part of the n-type InP barrier layer 4 and n-type In _0.8 Ga _0.2
As _{0. The} etching shape applied to the ₄ P _0.6 diffraction grating layer 5 is well retained. Further, since the n-type InP cap layer 6 is formed as thick as 0.2 μm and serves as a supply source of sufficient constituent elements, the diffraction grating 12 is completely covered by the n-type first InP clad layer 16 formed by mass transport. .

After the heat treatment, the n-type second InP clad layer 8
Is laminated at a crystal growth temperature TG2 of 560 ° C. for 0.5 μm. Since the diffraction grating 12 is already covered with the n-type first InP cladding layer 16 formed by mass transport, the shape change does not occur even when heated by the crystal growth temperature TG2, and since the temperature is high, sufficient surface diffusion is achieved. It becomes possible and no crystal defect occurs in the step portion of the diffraction grating.

After crystal growth of the n-type second InP clad layer 8, mesa etching for the purpose of forming an optical waveguide and a current block structure for the purpose of current confinement are formed (not shown). Contact layer 9 to 1
After stacking up to a thickness of μm and finishing all epitaxial crystal growth (FIG. 6D), the n-electrode 10,
The p-electrode 11 is laminated on the back side of the wafer, and the wafer process is completed. After that, both surfaces are cleaved to form end face reflection films on the front and rear end faces, and chip separation is performed to obtain a semiconductor laser operating in a single mode.

In the thus obtained semiconductor laser of the second embodiment, the shape of the diffraction grating after the element is completed is kept substantially the same as that immediately after etching. The side surface angle 13 of the diffraction grating after the element is completed is substantially the same as that after etching and is 70 degrees or more and less than 90 degrees, and is typically about 80 degrees. The n-type second InP cladding layer 8 in which the diffraction grating is embedded is formed.
It was confirmed by transmission electron microscope observation that almost no crystal defects were generated in.

In the semiconductor laser manufacturing method described above, the heat treatment temperature TG3 is 500 ° C. and the n-type second InP is used as an example.
Although the crystal growth temperature TG2 of the cladding layer 8 is 560 ° C., if the crystal growth temperature TG2 is 540 ° C. or higher and 580 ° C. or lower and the temperature difference between the crystal growth temperature TG2 and the heat treatment temperature TG3 is 50 to 70 ° C. The same effect can be obtained.

In the method of manufacturing the semiconductor laser described above, the layer thickness of the n-type InP cap layer 6 is 0.2 μm as an example, but the same effect can be obtained if the layer thickness is 0.15 μm or more and 0.3 μm or less.

Further, in the above-mentioned semiconductor laser manufacturing method, the case where the MOCVD method is applied as the epitaxial crystal growth method has been shown, but the same effect can be obtained by other epitaxial crystal growth methods (for example, MBE method). Needless to say.

As described above, according to the semiconductor laser and the method of manufacturing the same in the second embodiment, the n-type InP cap layer is formed on the diffraction grating layer, and the heat treatment temperature TG3 is set to the n-type second I2.
Since the temperature was set relatively low with respect to the crystal growth temperature TG2 of the nP clad layer, the shape of the diffraction grating was maintained and crystal defects were hardly generated in the step portion of the diffraction grating. As the fluctuation of the coupling constant is suppressed, the controllability of the coupling constant is improved and the element characteristics are stabilized, and the deterioration of the element is suppressed and the reliability of the element is improved.

[0050]

According to the semiconductor laser of the present invention, a first conductivity type InP substrate, a first conductivity type InP buffer layer formed on the first conductivity type InP substrate, and the first conductivity type InP substrate are provided.
An active layer formed on the conductive InP buffer layer, a second conductive InP barrier layer sequentially formed on the active layer, a second conductive InGaAsP diffraction grating layer, and a second conductive layer.
A diffraction grating which is composed of conductive InP cap layers and which is continuously repeated at a predetermined period along the optical waveguide direction, and a second diffraction grating which is sequentially formed on the main surface of the wafer including the diffraction grating. Conductive type first InP clad layer, second conductive type second InP clad layer, and second conductive type InP
Since the contact layer is provided, and the angle between the side surface of the diffraction grating and the main surface of the wafer in the optical waveguide direction is 70 degrees or more and less than 90 degrees, fluctuations in the coupling constant are suppressed against variations in duty that are unavoidable in the manufacturing process. As a result, the controllability of the coupling constant is improved and the device characteristics are stabilized.

In the semiconductor laser according to the present invention, the layer thickness of the second conductivity type first InP clad layer is 0.02.
Since the thickness is 5 μm or more and 0.1 μm or less, crystal defects are hardly generated in the step portion of the diffraction grating, so that the deterioration of the element is suppressed and the reliability of the element is improved.

In the method of manufacturing a semiconductor laser according to the present invention, the step of forming a diffraction grating on the main surface of the wafer and the epitaxial crystal growth of the first semiconductor layer on the main surface of the wafer including the diffraction grating at the crystal growth temperature TG1. And a step of epitaxially growing a second semiconductor layer on the first semiconductor layer at a crystal growth temperature TG2.
Since the crystal growth temperature TG1 is set to be 50 to 70 ° C. lower than the crystal growth temperature TG2, the shape of the diffraction grating is maintained and crystal defects are hardly generated in the step portion of the diffraction grating, which is an unavoidable duty in the manufacturing process. As a result of suppressing the variation of the coupling constant with respect to the variation, the controllability of the coupling constant is improved and the element characteristics are stabilized, and the element deterioration is suppressed, and the element reliability is improved.

In the method for manufacturing a semiconductor laser according to the present invention, after the step of epitaxially growing the second semiconductor layer, the angle between the side surface of the diffraction grating and the main surface of the wafer in the optical waveguide direction is 70 degrees or more. Since the angle is less than 90 degrees, the variation of the coupling constant is suppressed with respect to the duty variation which is unavoidable in the manufacturing process. As a result, the controllability of the coupling constant is improved and the element characteristics are stabilized.

In the method for manufacturing a semiconductor laser according to the present invention, the first conductivity type IP substrate is formed on the first conductivity type InP substrate.
nP buffer layer, active layer, second conductivity type InP barrier layer, second conductivity type InGaAsP diffraction grating layer, and second
A step of sequentially epitaxially growing each layer of the conductivity type InP cap layer, the second conductivity type InP barrier layer, the second conductivity type InGaAsP diffraction grating layer, and the second conductivity type by a lithography technique and a dry etching technique. In the InP cap layer, a step of forming a diffraction grating that is continuously repeated at a predetermined period along the optical waveguide direction, and a second conductivity type first InP clad layer on the main surface of the wafer including the diffraction grating. A step of growing an epitaxial crystal and a second step on the first conductivity type InP clad layer.
Second conductivity type InP cladding layer and second conductivity type In
A step of sequentially performing epitaxial crystal growth on the P contact layer, and a crystal growth temperature T when epitaxially growing the second conductivity type first InP clad layer.
G1 is 5 from the crystal growth temperature TG2 at the time of epitaxial crystal growth of the second conductivity type second InP clad layer.
Since the temperature is kept at 0 to 70 ° C., the shape of the diffraction grating is maintained and crystal defects are hardly generated in the step portion of the diffraction grating, so that the variation of the coupling constant is suppressed against the duty variation unavoidable in the manufacturing process. The effect of improving the controllability of the coupling constant and stabilizing the element characteristics, and the effect of suppressing element deterioration and improving the element reliability are obtained.

In the method for manufacturing a semiconductor laser according to the present invention, the first conductivity type IP substrate is formed on the first conductivity type InP substrate.
nP buffer layer, active layer, second conductivity type InP barrier layer, second conductivity type InGaAsP diffraction grating layer, and second
A step of sequentially epitaxially growing each layer of the conductivity type InP cap layer, the second conductivity type InP barrier layer, the second conductivity type InGaAsP diffraction grating layer, and the second conductivity type by a lithography technique and a dry etching technique. Forming a diffraction grating that is continuously repeated at a predetermined period along the optical waveguide direction on the InP cap layer, and melting the second conductivity type InP cap layer by mass transport by heat treatment. A step of forming a second conductivity type first InP cladding layer covering the main surface of the wafer including the diffraction grating, and the second conductivity type first InP
A step of sequentially epitaxially growing a second conductivity type second InP clad layer and a second conductivity type InP contact layer on the clad layer, wherein the second conductivity type InP cap layer is heat-treated. Heat treatment temperature T
From the crystal growth temperature TG2 when epitaxially growing the second conductivity type second InP clad layer, G3 is set to 5
Since the temperature is kept at 0 to 70 ° C., the shape of the diffraction grating is maintained and crystal defects are hardly generated in the step portion of the diffraction grating, so that the variation of the coupling constant is suppressed against the duty variation unavoidable in the manufacturing process. The effect of improving the controllability of the coupling constant and stabilizing the element characteristics, and the effect of suppressing element deterioration and improving the element reliability are obtained.

Further, in the method of manufacturing a semiconductor laser according to the present invention, the second conductivity type InP cap layer is formed by 0.15.
Since the size is set to be not less than μm and not more than 0.3 μm, the shape of the diffraction grating is maintained, so that the fluctuation of the coupling constant is suppressed against the duty variation that is unavoidable in the manufacturing process. It has the effect of stabilizing the characteristics.

Further, in the method of manufacturing a semiconductor laser according to the present invention, the crystal growth temperature TG2 is set in the range of 540 to 580 ° C., so that the shape of the diffraction grating is maintained and crystal defects are hardly generated in the step portion of the diffraction grating. Since it does not occur, fluctuations in the coupling constant are suppressed against variations in duty that are unavoidable in the manufacturing process. As a result, the controllability of the coupling constant is improved and element characteristics are stabilized, and element deterioration is suppressed, and element reliability is reduced. Has the effect of improving.

Further, in the method of manufacturing a semiconductor laser according to the present invention, after the step of sequentially epitaxially growing the second conductivity type second InP cladding layer and the second conductivity type InP contact layer, the above-mentioned process in the optical waveguide direction is performed. Since the angle between the side surface of the diffraction grating and the main surface of the wafer is set to 70 degrees or more and less than 90 degrees, the variation of the coupling constant is suppressed against the duty variation that is unavoidable in the manufacturing process. As a result, the controllability of the coupling constant is improved. Element characteristics are stable.

[Brief description of drawings]

FIG. 1 is a diagram showing the method of manufacturing the semiconductor laser according to the first embodiment.

FIG. 2 is an MQW in the semiconductor laser according to the first embodiment.
It is sectional drawing which shows the structure of an active layer.

FIG. 3 is a sectional view of a part of a diffraction grating in the semiconductor laser according to the first embodiment.

FIG. 4 is a diagram showing a variation of a coupling constant with respect to a duty of a semiconductor laser when a side surface angle of a diffraction grating is 40 degrees and 80 degrees.

FIG. 5 is a diagram showing coupling constant fluctuations when the side angle of the diffraction grating is 40 degrees and 80 degrees and the duty of the semiconductor laser fluctuates by 50 ± 10%.

FIG. 6 is a diagram showing the method of manufacturing the semiconductor laser according to the second embodiment.

FIG. 7 is a diagram showing a conventional method for manufacturing a semiconductor laser.

FIG. 8 is a diagram showing another conventional method for manufacturing a semiconductor laser.

[Explanation of symbols]

1 p-type InP substrate, 2 p-type InP buffer layer,
3 multiple quantum well layers (MQW layers), 4 n-type InP burrs
A layer, 5 n-type In_0.8Ga_0.2As _0.4P
_0.6Diffraction grating layer, 6 n-type InP cap layer, 7
  n-type first InP cladding layer, 8 n-type second InP cladding layer
Rad layer, 9 n-type InP contact layer, 10 n
Electrode, 11 p electrode, 12 diffraction grating, 13 times
Side angle of folded grid, 14 In_0.8Ga_0.2As
_0.9P_0.1Well layer, 15In_0.7Ga_0.3
As_0.6P_0.4Barrier layer, 16 mass transfer
N-type first InP cladding layer formed by
18 n-type InP buffer on 17 n-type InP substrate
Layer, 19 In_0.72Ga_0.28As_{0.6 1}P
_0.39Active layer, 20 p-type In_0.85Ga
_0.15As_0.33P_{0 ． 67}Light guide layer, 21
p-type InP cap layer, 22 p-type InP clad
Layer, 23 n-type InGaAsP guide layer, 24 I
nGaAsP active layer, 25p type InGaAsP guide
Layer, 26 p-type InP layer, 27 p-type InGaAs
P diffraction grating layer, 28 p-type InGaAsP contact
layer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyuki Murasaki             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Yasuo Nakajima             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F term (reference) 5F073 AA13 AA64 AA74 CA12 DA05                       EA28

Claims (9)

[Claims] 1. A first-conductivity-type InP substrate, a first-conductivity-type InP buffer layer formed on the first-conductivity-type InP substrate, and a first-conductivity-type InP buffer layer. An active layer and a second layer sequentially formed on the active layer.
Conductive InP barrier layer, second conductive InGaAsP
A diffraction grating which is composed of a diffraction grating layer and a second conductivity type InP cap layer and which is continuously repeated at a predetermined period along the optical waveguide direction, and on the wafer main surface including the diffraction grating. Sequentially formed second conductivity type first In
A P-cladding layer, a second conductivity-type second InP clad layer, and a second conductivity-type InP contact layer, and an angle between the side surface of the diffraction grating and the wafer main surface in the optical waveguide direction is 70 degrees or more and less than 90 degrees. A semiconductor laser characterized by: 2. The semiconductor laser according to claim 1, wherein a layer thickness of the second conductivity type first InP cladding layer is 0.025 μm or more and 0.1 μm or less. 3. A step of forming a diffraction grating on the main surface of the wafer, and a crystal growth temperature T on the main surface of the wafer including the diffraction grating.
G1 comprises epitaxially growing a first semiconductor layer on the first semiconductor layer, and G2 is a second semiconductor layer grown on the first semiconductor layer at a crystal growth temperature TG2. A method for manufacturing a semiconductor laser, wherein TG1 is 50 to 70 ° C. lower than the crystal growth temperature TG2. 4. After the step of epitaxially growing the second semiconductor layer, the angle between the side surface of the diffraction grating and the main surface of the wafer in the optical waveguide direction is 70 degrees or more and less than 90 degrees. Item 3. A method of manufacturing a semiconductor laser according to item 3. 5. An InP buffer layer of the first conductivity type, an active layer, an InP barrier layer of the second conductivity type, an InGaAsP diffraction grating layer of the second conductivity type, and a second conductivity type on an InP substrate of the first conductivity type. Step of sequentially performing epitaxial crystal growth on each of the InP cap layers, the second conductivity type InP barrier layer, the second conductivity type InGaAsP diffraction grating layer, and the second conductivity type InP by a lithography technique and a dry etching technique. A step of forming a diffraction grating which is continuously repeated at a predetermined period along the optical waveguide direction on the cap layer, and an epitaxial crystal of a second conductivity type first InP clad layer on the main surface of the wafer including the diffraction grating. Growing step and second conductivity type second InP cladding layer and second conductivity type InP contact layer on the second conductivity type first InP cladding layer And a step of sequentially performing epitaxial crystal growth on the first conductivity type InP of the second conductivity type.
The crystal growth temperature TG1 for epitaxially growing the cladding layer is the same as the crystal growth temperature TG2 for epitaxially growing the second conductivity type second InP cladding layer.
A method of manufacturing a semiconductor laser, wherein the temperature is lower by 50 to 70 ° C. 6. An InP buffer layer of the first conductivity type, an active layer, an InP barrier layer of the second conductivity type, an InGaAsP diffraction grating layer of the second conductivity type, and a second conductivity type on an InP substrate of the first conductivity type. Step of sequentially performing epitaxial crystal growth on each of the InP cap layers, the second conductivity type InP barrier layer, the second conductivity type InGaAsP diffraction grating layer, and the second conductivity type InP by a lithography technique and a dry etching technique. A step of forming a diffraction grating that is continuously repeated at a predetermined period along the optical waveguide direction in the cap layer, and melting the second conductivity type InP cap layer by mass transport by heat treatment to perform the diffraction. First conductivity type second In covering the main surface of the wafer including the lattice
Forming a P clad layer, and forming a first clad layer of the second conductivity type
A step of sequentially epitaxially growing a second conductivity type second InP clad layer and a second conductivity type InP contact layer on the InP clad layer.
The heat treatment temperature TG3 for heat treatment of the conductivity type InP cap layer is the crystal growth temperature TG2 for epitaxial crystal growth of the second conductivity type second InP clad layer.
A method of manufacturing a semiconductor laser, wherein the temperature is lower by 50 to 70 ° C. 7. The method of manufacturing a semiconductor laser according to claim 6, wherein the InP cap layer of the second conductivity type has a thickness of 0.15 μm or more and 0.3 μm or less. 8. The crystal growth temperature TG2 is 540 to 58.
8. The method for manufacturing a semiconductor laser according to claim 3, wherein the temperature is in the range of 0 ° C. 9. The angle formed between the side surface of the diffraction grating and the main surface of the wafer in the optical waveguide direction after the step of sequentially epitaxially growing the second conductivity type second InP cladding layer and the second conductivity type InP contact layer. Is over 70 degrees 9
9. The method for manufacturing a semiconductor laser according to claim 5, wherein the angle is less than 0 degree.