JPH06216463A - Semiconductor laser apparatus and manufacture thereof - Google Patents

Abstract

PURPOSE:To thin a lower clad layer by restraining diffusion of acceptor impurities into the lower clad layer from a p-type substrate. CONSTITUTION:A p-type lower clad layer 3 is grown on a p-type substrate in such a manner that an undoped epitaxial layer 2 of predetermined thickness is grown between the clad layer and the substrate. At this time, time for growing the undoped layer is adjusted by diffusion of acceptor from the substrate to make a carrier distribution of the undoped layer part at least euqal level to that of the lower clad layer. As a result, diffusion of p-type impurities from the substrate can be reduced and thickness of the lower clad layer can be made thin. Accordingly, time for crystal growth can be reduced and materials can be saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly, to a semiconductor laser device in which deterioration of laser characteristics due to impurity diffusion from a substrate into a lower clad layer at the time of manufacturing is suppressed. The present invention relates to a method for manufacturing a semiconductor laser device that can be manufactured with a small number of materials.

[0002]

2. Description of the Related Art FIG. 2 (a) is a sectional view of a wafer after a first crystal growth step in a conventional method for manufacturing a semiconductor laser device, in which 1 is a p-type InP substrate and 6 is a p-type InP substrate.
A P lower clad layer, 4 is an InGaAsP active layer, and 5 is an n-type InP first upper clad layer. Here, Zn is generally used as the p-type impurity. The carrier concentration of the substrate 1 is generally about 4 to 6 × 10 ¹⁸ cm ⁻³ , and the carrier concentration of the lower cladding layer 2 is generally on the order of 10 ¹⁷ cm ⁻³ .

Next, a method of manufacturing a semiconductor laser device from the double heterostructure wafer shown in FIG.
Will be described. On a wafer prepared by sequentially epitaxially growing a p-type InP lower clad layer 6, an InGaAsP active layer 4, and an n-type InP upper clad layer 5 on the p-type InP substrate 1 by, for example, a metal organic chemical vapor deposition (MOCVD) method. A resist is applied, and this is photoengraved to obtain the image shown in FIG.
A stripe-shaped resist pattern as shown in FIG. 3A is formed, and etching is performed using this resist pattern as a mask to form stripe-shaped grooves as shown in FIG. 3B. Next, after removing the resist pattern, the p-type InP burying layer 7 and the n-type In are formed by a liquid phase growth method.
A P block layer 8, a p-type InP block layer 9, then an n-type InP second upper cladding layer 10, and an n-type InGaAsP contact layer 11 are formed. As a result, a laser structure called BH (buried heterostructure) type is formed. Then, as shown in FIG. 3 (d), after the entire laser structure is mesa-etched, an insulating film 12 such as SiO2 is formed on the wafer, and an opening is provided in a portion of the insulating film 12 corresponding to the upper part of the active layer 4. An n-side electrode (negative electrode) 13 is provided so as to contact the contact layer 11 at the opening, and p is provided on the back surface of the substrate 1.
The semiconductor laser device is completed by providing the side electrode (positive electrode) 14.

FIG. 2B is a diagram showing a profile of the p-type impurity concentration NA after the semiconductor laser is completed. The position x in the depth direction from the active layer 4 is the abscissa, and the p-type impurity concentration NA for this is shown. Is on the vertical axis. As shown in FIG. 2B, diffusion of p-type impurities from the substrate 1 into the epitaxial layer occurs in the completed crystal.

[0005]

As described above, the conventional method for manufacturing a semiconductor laser device has a p-type I on a p-type InP substrate.
Since the nP clad layer is directly grown and p-type impurities are diffused from the substrate into the epitaxial layer in the manufacturing process, there are the following problems.

That is, in the semiconductor laser device manufactured as described above, the holes and electrons injected from the positive electrode 14 and the negative electrode 13 emit light in the active layer 4, but the light oscillated at this time rises and falls. It has a spread of about 1 μm to the clad layers 5 and 6.

For this reason, if a high concentration of impurities is present in the upper and lower cladding layers 5 and 6 within 1 μm or less of the active layer 4, absorption loss due to free carrier absorption of light occurs there, and the light emission efficiency decreases. The diffusion distance of the p-type impurity from the substrate shown in FIG. 2B depends on the carrier concentration of the lower cladding layer, and when the carrier concentration of the lower cladding layer is high, diffusion of 1 μm or more may occur. In such a case, in order to prevent the above-mentioned decrease in luminous efficiency, it is necessary to increase the growth layer thickness of the lower cladding layer to 2-3 μm.
Since a large amount of growth raw material is required, the cost is high and the growth time is long.

The present invention has been made in order to solve the above problems, and manufactures a semiconductor laser device capable of suppressing the diffusion of p-type impurities from the substrate without increasing the thickness of the lower cladding layer. It is intended to provide a way.

[0009]

In the method of manufacturing a semiconductor laser device according to the present invention, a crystal growth of an undoped layer having a predetermined thickness is performed between a p-type substrate and a p-type lower cladding layer to form a crystal from the substrate. It suppresses the diffusion of p-type impurities.

[0010]

According to the present invention, the undoped layer growth performed between the substrate and the lower clad layer suppresses the diffusion of impurities from the substrate, so that the lower clad layer can be made thin, which shortens the growth time in crystal growth. You can do it and save material.

[0011]

EXAMPLES Example 1. FIG. 1A is a sectional view of a wafer after a first crystal growth step in a method for manufacturing a semiconductor laser device according to a first embodiment of the present invention, in which 1 is p
-Type InP substrate, 2 is an undoped I substrate grown on the substrate 1.
nP layer, 3 is a p-type InP lower clad layer grown on the undoped InP layer 2, 4 is an InGaAsP active layer grown on the lower clad layer 3, and 5 is an n layer grown on the active layer 4. It is a type InP first upper cladding layer.

The manufacturing method for completing the semiconductor laser device from the wafer after the first crystal growth step shown in FIG.
The conventional example is the same as that shown in FIGS.

In this embodiment, at the time of the first crystal growth shown in FIG. 1A, an undoped layer without acceptor doping is first grown on the substrate 1. Specifically, for example, on a p-type InP substrate having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ ,
First, an InP layer is grown undoped by a predetermined layer thickness by MOCVD or the like, and then, as usual, a p-type lower clad layer having a predetermined carrier concentration (of the order of 10 ¹⁷ cm ⁻³ ) and InGa.
An AsP active layer and an n-type InP first upper clad layer are sequentially epitaxially grown. The wafer shown in FIG. 1 (a) is formed by continuously performing the above crystal growth steps.

Here, regarding the epitaxial growth of the undoped InP layer, the heat treatment applied until the semiconductor laser device is completed, that is, the first crystal growth step, and the second crystal growth by the liquid phase growth shown in FIG. 3C are performed. Depending on the process or the like, the undoped growth region becomes p-type due to the p-type impurities diffusing from the p-type InP substrate and the p-type InP lower cladding layer, and the carrier concentration is about the same as or higher than that of the p-type lower cladding layer 3. The growth time is controlled so that it becomes thick.

FIG. 2 shows a growth temperature of 650 ° C. and a growth pressure of 150.
When an InP layer with various carrier concentrations was grown on a p-type InP substrate with a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ under a torr, V / III ratio of −140, and a growth rate of 1 μm / hr for 3 hours. FIG. 3 is a diagram showing a diffusion distance of Zn from a substrate into a growth layer. As can be seen from this figure, the diffusion distance of the p-type impurity from the substrate into the epitaxial layer depends on the carrier concentration of the epitaxial layer, and the lower the carrier concentration, the shorter the diffusion distance. The thickness of the InP layer 2 to be grown undoped varies depending on the total growth time, but is, for example, 0.
It is appropriate that the thickness is about 5 μm to 1.0 μm.

FIG. 1B is a diagram showing a profile of the p-type impurity concentration NA after the semiconductor laser is completed. The position x in the depth direction from the active layer 4 is the horizontal axis, and the p-type impurity concentration NA corresponding thereto is shown. Is on the vertical axis. In this embodiment, as shown in FIG. 1 (b), p
The diffusion of the type impurities remains within the undoped InP layer 2 and does not diffuse into the p-type InP lower cladding layer 3. Therefore, if the p-type InP lower cladding layer 3 has a layer thickness corresponding to the spread of the laser light, it is possible to sufficiently suppress the reduction of the light emission efficiency due to the absorption loss due to the absorption of free carriers of the light.

As described above, in this embodiment, the p-type InP lower cladding layer 3 can have a minimum thickness, for example, about 1 μm, and as described above, the layer thickness of the undoped growth region can be 1 μm or less. Therefore, the layer thickness of the epitaxial layer forming the p-type InP lower cladding layer can be set to 2 μm or less, and the growth time can be shortened and the material can be saved as compared with the conventional case.

Example 2. In the first embodiment described above, the undoped semiconductor layer epitaxially grown on the substrate is InP which is the same crystal material as the substrate 1, but InGaAs or InGaAsP lattice-matched to InP forming the substrate as the undoped layer is shown. It is also possible to use ternary or quaternary mixed crystal materials such as.

FIG. 3 shows a growth temperature of 650 ° C. and a growth pressure of 150.
When an InGaAsP layer of various compositions was grown for 3 hours on a p-type InP substrate having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ under a torr, V / III ratio of 140 and a growth rate of 1 μm / hr, It is a figure which shows the diffusion distance of Zn from a board | substrate to a growth layer.

As shown in FIG. 3, the diffusion distance of Zn from the substrate into the growth layer decreases as the InGaAs component increases. That is, InGaAs or InG as an undoped layer
When a ternary or quaternary mixed crystal material such as aAsP is used, the acceptor diffusion distance is smaller than when InP is used as the undoped layer. Therefore, the crystal layer thickness of the undoped layer is, for example, about 0.1 to 0.5 μm. Even if it is thin, the sufficient effect can be obtained, and the process time can be further shortened and the material can be further saved as compared with the first embodiment.

In the first and second embodiments, InP is used.
Although the semiconductor laser device of the system has been shown, the present invention can be applied to the case of manufacturing a GaAs semiconductor laser device using a p-type GaAs substrate, and has the same effect as the above embodiment. AlGaAs, AlGaInP, or the like can be used as the undoped layer made of a ternary or quaternary mixed crystal material when applied to a GaAs semiconductor laser device.

[0022]

As described above, according to the present invention, after an undoped crystal layer having a predetermined layer thickness is epitaxially grown on a p-type substrate, a p-type substrate is formed on the p-type substrate on which the undoped layer is grown. Since the clad layer is epitaxially grown, the thickness of the lower clad layer can be reduced to the necessary minimum, and a semiconductor laser device having excellent characteristics can be manufactured with a short crystal growth time and a small amount of material.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a wafer structure after a first crystal growth step in a method for manufacturing a semiconductor laser device according to an embodiment of the present invention, and a diagram showing an impurity profile after laser completion.

FIG. 2 is a diagram showing a relationship between a diffusion distance of Zn from a substrate into a growth layer and a carrier concentration in the growth layer.

FIG. 3 is a diagram showing a relationship between a diffusion distance of Zn from a substrate into a growth layer and a material composition of the growth layer.

FIG. 4 is a cross-sectional view showing a wafer structure after a first crystal growth step in a conventional method for manufacturing a semiconductor laser device, and a diagram showing an impurity profile after completion of laser.

FIG. 5 is a diagram showing a manufacturing process of a conventional semiconductor laser device.

[Explanation of symbols]

 1 p-type InP substrate 2 undoped grown InP layer 3 p-type InP lower clad layer 4 InGaAsP active layer 5 n-type InP upper clad layer

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[Procedure amendment]

[Submission date] January 12, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

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Title: Method for manufacturing semiconductor laser device and half
Conductor laser

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[Claims]

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[0002]

2. Description of the Related Art FIG. 4 (a) is a sectional view of a wafer after a first crystal growth step in a conventional method for manufacturing a semiconductor laser device, in which 1 is a p-type InP substrate and 6 is a p-type InP substrate.
A P lower clad layer, 4 is an InGaAsP active layer, and 5 is an n-type InP first upper clad layer. Here, Zn is generally used as the p-type impurity. The carrier concentration of the substrate 1 is generally about 4 to 6 × 10 ¹⁸ cm ^-3 , and the carrier concentration of the lower cladding layer 2 is generally on the order of 10 ¹⁷ cm ^-3 .

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[0003] Next, FIG. 5 illustrates a method of manufacturing a semiconductor laser device from wafer double heterostructure shown in Figure 4 (a). On a wafer prepared by sequentially epitaxially growing a p-type InP lower cladding layer 6, an InGaAsP active layer 4, and an n-type InP upper cladding layer 5 on the p-type InP substrate 1 by, for example, a metal organic chemical vapor deposition (MOCVD) method. A resist is applied, and this is photolithographically processed as shown in Fig. 5 (a).
A stripe-shaped resist pattern as shown in, by etching using the resist pattern as a mask, as shown in FIG. 5 (b), to form a striped mesa <br/>. Next, after removing the resist pattern, the p-type InP burying layer 7, the n-type InP block layer 8, the p-type InP block layer 9, and then the n-type InP are formed by liquid phase epitaxy.
The second upper cladding layer 10 and the n-type InGaAsP contact layer 11 are formed. As a result, a laser structure called BH (buried heterostructure) type is formed. Then figure
As shown in FIG. 5 (d), after the entire laser structure is mesa-etched, an insulating film 12 such as SiO2 is formed on the wafer,
An opening is provided in a portion of the insulating film 12 corresponding to the upper part of the active layer 4, and an n-side electrode (negative electrode) 13 is provided so as to contact the contact layer 11 at the opening. A p-side electrode (positive electrode) 14 is provided on the back surface of the substrate 1. The semiconductor laser device is completed by providing.

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[0004] FIG. 4 (b) is a view showing a profile of the semiconductor after the laser completion of p-type impurity concentration NA, the position x in a depth direction from the active layer 4 on the horizontal axis, the p-type impurity concentration NA to this Is on the vertical axis. As shown in FIG. 4 (b), p-type impurities are diffused from the substrate 1 into the epitaxial layer in the completed crystal.

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As described above, in this embodiment, the p-type InP lower cladding layer 3 can have a minimum thickness, for example, about 1 μm, and as described above, the layer thickness of the undoped growth region can be 1 μm or less. since, p-type InP lower cladding layer may be a 2μm or less the thickness of the epitaxial layer constituting the, compared to the conventional, the <br/> also to be able shortened growth time, saving material.

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor laser device having a p-type lower clad layer having an impurity concentration lower than that of the p-type substrate on a p-type substrate, wherein an epitaxial layer having a predetermined layer thickness is formed on the p-type substrate. A method of manufacturing a semiconductor laser device, comprising: an undoped growth step; and a step of epitaxially growing the p-type lower cladding layer on the undoped growth epitaxial layer. 2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the undoped growth layer is made of the same crystalline material as the substrate. 3. The method for manufacturing a semiconductor laser device according to claim 1, wherein the undoped growth layer is a ternary or quaternary mixed crystal material.