JPH02263492A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To make a manufacturing process simple and obtain a highly reliable quantum well laser at a high yielding rate by replacing processes, i.e., vapor deposition of Si, adhesion of a Si3N4 film, and thermal annealing with those of 'on the spot' deposition of Si and thermal annealing that are performed in an epitaxial growth device. CONSTITUTION:The 1st clad layer 2, a quantum well active layer 3 consisting of a three-layer: photoguide layer - quantum well layer - photoguide layer, a p-type clad layer 4 as the 2nd clad layer, and a contact layer 5 are treated one after the other with organometal vapor phase epitaxy (MOVPE growth) on an n-type GaAs substrate 1 and a substrate crystal is obtd. Subsequently, SiH4 or Si2H6 gas is introduced in a device and the substrate crystal is exposed to the gas. This state allows laser beams 11 to irradiate on the surface of the substrate crystal and Si to perform deposition and then two pieces of Si films 80 are formed into the stripe shaped. Further, the stripes like Si films 80 which are obtained by heating the substrate crystal after putting it as it is in the device and by performing deposition are diffused thermally in the substrate crystal. This approach solves problems of a diffusion process of Si where its process is complicated and distortions appear in the case of thermal annealing for diffusion and a semiconductor laser which is simple and is superior in laser oscillation characteristics and reliability is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor laser, and in particular, a method for manufacturing a semiconductor laser, which has a quantum well as an active layer and a buried structure utilizing mixed crystallization of the quantum well by introducing impurities. This invention relates to a method for manufacturing a quantum well laser.

[Conventional technology]

In order to use a semiconductor laser as a light source for optical communication or optical information processing, it is required to oscillate in a stable fundamental transverse mode when driven with a pulse or direct current, regardless of the magnitude of the current. In order to stably obtain the fundamental transverse mode, it is common to form an artificial refractive index distribution in a direction parallel to the active layer, that is, in the lateral direction. Conventionally, as this type of semiconductor device laser, a semiconductor laser has been proposed in which a quantum well is used in an active region and a lateral refractive index distribution is formed by utilizing mixed crystal formation of the quantum well by impurity diffusion.

Figure 2 is a cross-sectional view perpendicular to the cavity direction showing an example of such a semiconductor laser, and a similar one is published in Applied Physics Letters.
Letters), Vol. 50, No. 23 (1987), pages 1637 to 1639. In FIG. 2, 1 is a substrate, 2 is a first cladding layer, 3 is a quantum well active layer, 4 is a second cladding layer, 5 is a contact layer, 6 is an insulating film, 7 is a diffusion region, 8 and 9 are electrodes. It is.

FIG. 3 shows the manufacturing process of this conventional semiconductor laser.

Metal organic vapor phase epitaxy (Metal Organic Vapor Ph
AseEpitaxy (hereinafter abbreviated as MOVPE) method was used to form an n-type Affi film with a thickness of 1 μm as the first ground layer.
o, tGa□, 3AS cladding layer 2, thickness 0.1 μm each
Undoped A lo, zs G a O,? S.A.
A quantum well active layer 3 consisting of an undoped GaAs single-ff well with a thickness of 100 mm is sandwiched between S light guide layers from both sides, and a p-type A 1 with a thickness of 1 μm serves as a second cladding layer.
g, qG 80.3AS cladding layer 4, thickness 0.1
A p-type GaAs:t cladding layer 5 of 5 μm is laminated (FIG. 3(b)).

Next, except for the striped active region that oscillates,
St to n-type Al 6. ? Ga 0.3A S diffuses to a depth reaching the cladding layer 2, but the diffusion of Si is 2
It is done in a step process. First, a 400-thick Si film 70 and a 900-thick St:+N4 film 71 are sequentially deposited on the surface of the p-type GaAs contact layer 5 by vapor phase growth (FIG. 3(C)). Ar'' laser beam 10 is irradiated onto a desired striped area from above to form a p-type G
aAs contact layer5. P-type A lo, ? A.S.
o, 2G a cladding layer 4. The quantum well active layer 3 is melted to infiltrate Si into the crystal (Fig. 3(d)).
.

Next, the crystal is annealed at 850"C for 0.7 hours, and Si is again diffused to the desired depth. The region 7 where Si is diffused becomes n-type, and the quantum well active layer 3 becomes Al o, zsG a 0.7SA The S light guide layer and the GaAs quantum well interdiffuse and become mixed crystal.The mixed crystal region has a lower refractive index than the unmixed region, and the effective The forbidden band width increases.

Next, an SiO or 5t3N4 insulating film 6 is deposited on the p-type GaAs contact N5 so as to cover the n-type diffusion region 7 in which Si is diffused in a stripe shape and expose the active region. An AuZn-based p-type electrode 8 is deposited on the insulating film 6 so as to make ohmic contact with the P-type GaAs contact layer 5, and then an AuGeNi-based n-type electrode 9 is deposited on the back surface of the n-type GaAs base Fi1. A semiconductor laser structure as shown in FIG. 3(e) was obtained. If this is folded in a direction perpendicular to the resonator and the folded surface is used as a Fobbly-Perot resonator reflection surface, the quantum well laser shown in FIG. 2 is completed.

In the semiconductor laser manufactured as described above, the active region has a structure in which the forbidden band width is wide (surrounded by a semiconductor layer with a small refractive index), and the refractive index distribution is sharp in the lateral direction. Since such a semiconductor laser has good light and current confinement efficiency, it oscillates with a low threshold current and has a stable fundamental transverse mode.

[Problem to be solved by the invention]

However, in the conventional manufacturing method described above, the Si diffusion process is complicated, and the thermal expansion coefficients of Si and N4 films and GaAS are different, so distortion occurs during thermal annealing for diffusion, which affects the oscillation characteristics of the semiconductor laser.

There are problems such as loss of reliability.

An object of the present invention is to provide a manufacturing method that solves these problems and allows a simple semiconductor laser with excellent laser oscillation characteristics and reliability to be obtained.

[Means to solve the problem]

The method for manufacturing a semiconductor laser of the present invention includes a quantum well structure including at least a first cladding layer of the first conductivity type and at least two types of semiconductor layers on a semiconductor substrate of the first conductivity type; a quantum well active layer with a narrow forbidden band width and a large refractive index; a second cladding layer of a second conductivity type with a wider forbidden band width than the quantum well active layer and a lower refractive index; An epitaxial growth process in which a substrate crystal is obtained by successively epitaxially growing a narrow electrode contact layer, and an energy beam extending parallel to two stripes on the substrate crystal surface while exposing the substrate crystal surface to an impurity gas atmosphere containing a first conductivity type impurity element. irradiating the impurity of the first conductivity type in stripes on the substrate crystal under the irradiation area; heating the substrate crystal to diffuse the precipitated impurity under the irradiation area; and an impurity diffusion step of making the electrode contact layer, the second cladding layer, and the quantum well active layer under the irradiation region have a first conductivity type, and making the quantum well active layer mixed crystal under the irradiation region. It is characterized by containing.

As the energy beam, a laser beam or a beam of charged particles such as electrons can be used.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a process diagram illustrating an embodiment of the present invention,
The manufacture of a semiconductor laser having the structure shown in FIG. 2 will be described.

First, the n-type GaAs substrate 1 is cleaned with an organic solvent and chemically etched to clean it, and then introduced into a MOVPE apparatus (FIG. 1(a)). On this n-type GaAs substrate 1, an n-type A 1! with a thickness of 1.0 μm is formed as a first cladding layer. ,
O,? Ga 0.3A S cladding layer 2 (Si doped; concentration l×10111cII-″), thickness 0.1 μm
(7) n-type A f o, zsG ao, tsA
S optical guide layer (Si doped; concentration I Xl0I7c
+a-3) and 100mm thick undoped GaAs single quantum well layer and 0.1μm thick p-type A lo,zs
A quantum well active layer 3 consisting of three layers: G ao, tsA s light guide layer (Zn doped; concentration I
10. ? G ao, xA S cladding layer 4 (Z
n-doped; concentration 1×101″cIl-″), thickness 0.1
5 μm p-type GaAS contact layer 5 (Zn doped;
Sequential MOVPE growth is performed at a concentration of I
FIG. 1(b)) is obtained.

Next, without taking the substrate crystal out of the MOVPE equipment,
E Introduce SiH4 or Si, H, gas into the apparatus and expose the substrate crystal to the gas. In this state, the spot size is 1 μm.
An Ar'' laser beam 11 focused on the crystal surface of the substrate is irradiated and scanned linearly to precipitate Si in two stripes to form two stripe-shaped Si films 80 (first
Figure (C)).

The power of the "Ar" laser is adjusted in the range of 0.01 to IW to prevent the temperature of the substrate crystal surface from rising excessively.For example, if the temperature is kept at about 650°C, St will precipitate, but the substrate crystal surface will not rise too much. The possibility of melting or introducing defects due to thermal distortion is small and appropriate.

If the striped Si film 80 has a thickness of about 10 to 100 layers, it can be used as a diffusion source in a subsequent diffusion step. Furthermore, two stripes of Si are precipitated, and the interval between them defines the width of the laser oscillation region (active amount region).

Since St moves in the next diffusion process and the actual active region width becomes narrower than the stripe spacing, the stripe spacing must be at least 1 μm in consideration of this.

Next, the substrate crystal is heated as it is in the MOVPE apparatus to thermally diffuse the striped Si deposited in the above process into the substrate crystal. As a substrate heating method, MOV
The same method used for PE growth, ie lamp heating or radio frequency heating, may be used, or Ar'' laser beam or electron beam may be used as shown in Figure 1(d). The electron beam is designated by reference numeral 12.

When using lamp heating or high frequency heating, the entire substrate crystal is kept at 850°C for about 1 hour to form an n-type A
By diffusing Si to a depth reaching the 10.7G ao, sA S cladding layer 2, the n-type diffusion layer 7 can be formed. When using a laser beam or an electron beam, it is possible to scan so as to locally heat only the striped Si film 8o. In this case, adjust the irradiation power density to diffuse Si to the desired depth in a short time without melting the substrate crystal or creating defects.
It is possible to form a type diffusion layer 7.

Next, an n-type diffusion region 7 is placed on the p-type GaAs contact layer 5.
A Stow or 5isN4 insulating film 6 is deposited to cover the active region and expose the active region.

This can be done by ordinary thermal CVD method and photolithography. An AuZn-based n-type electrode 8 is formed on the insulating film 6 so as to make ohmink contact with the p-type GaAs contact layer 6.
Then, AuGe is deposited on the back surface of the n-type GaAS substrate 1.
By depositing an n-type electrode 9 made of Ni, a semiconductor laser structure as shown in FIG. 2(e) is obtained. If this is interfolded in a direction perpendicular to the resonator and the interfolded surface is used as a Folibero resonator reflection surface, the quantum well laser shown in FIG. 2 is completed.

Dry etching may also be used to obtain the resonator reflecting surface. In that case, it is also possible to carry out the process from the epitaxial growth process to the formation of the resonator reflective surface in a consistent dry process, in other words, in a series of vacuum apparatuses without exposing the substrate crystal to the atmosphere.

In addition, in the above-mentioned example, epitaxial growth and subsequent processes were performed using a MOVPE apparatus.
This may be molecular beam epitaxy or gas source molecular beam epitaxy using gas as a raw material.

In addition, as a material, Ga As / A I G
Although it was explained using the a A s system, other m-v, ■-m
Compound semiconductors, such as InGaA using an InP substrate
s/InP, InGaAsP/InP, InGaAs/
It goes without saying that materials such as InAffiAs, InGaP/InAlGaP, etc. may also be used.

〔Effect of the invention〕

As realized above, the manufacturing method of the present invention eliminates the evaporation of Si, the adhesion of Si3N4 film, which were necessary in the conventional manufacturing method.
The step of thermal annealing is replaced by "in-situ" Si deposition and thermal annealing performed in an epitaxial growth apparatus. Therefore, St.

There is no need to transfer the substrate crystal to another device for N4 deposition, which simplifies the process.

Furthermore, in the present invention, since the substrate crystal is not exposed to the atmosphere during the process, there is no deterioration of laser oscillation characteristics or reliability problems due to oxidation or contamination. Furthermore, the problem of strain being introduced from the Si:+N4 film during thermal annealing, which was a problem with conventional manufacturing methods, is eliminated.

Therefore, according to the present invention, a highly reliable quantum well laser can be obtained with high yield.

[Brief explanation of drawings]

FIG. 1 is a process cross-sectional view explaining the main steps of the manufacturing method of the present invention, FIG. 2 is a cross-sectional view showing an example of a quantum well laser, and FIG. 3 is a process step explaining the main steps of the conventional manufacturing method. FIG. 1...Substrate 2...First cladding layer 3...Quantum well active layer 4...Second cladding layer 5, 6, 7, 8, 9, 10, 11・ 12 ・ 70.80 ・ 71 ・ ・ ・ ・ Contact layer Insulating film Diffusion region n-type electrode

Claims (1)

[Claims] (1) It has a quantum well structure consisting of at least a first cladding layer of the first conductivity type and at least two types of semiconductor layers on a semiconductor substrate of the first conductivity type, and has a narrower forbidden band width and refractive index than the first cladding layer. A quantum well active layer with a large
An epitaxial growth step in which a cladding layer and an electrode contact layer having a narrower bandgap than the second cladding layer are sequentially epitaxially grown to obtain a substrate crystal, and an energy beam is applied to the substrate crystal surface while exposing it to an impurity gas atmosphere containing an impurity element of the first conductivity type. a step of irradiating the impurity of the first conductivity type in stripes on the substrate crystal under the irradiated area by irradiating the impurity to two stripe-shaped regions extending in parallel on the surface of the substrate crystal; and heating the substrate crystal. The precipitated impurities are diffused under the irradiation region, and the electrode contact layer, second cladding layer, and quantum well active layer under the irradiation region are made to have the first conductivity type, and the quantum well active layer is made to be of the first conductivity type. 1. A method for manufacturing a semiconductor laser, comprising the step of diffusing an impurity to form a mixed crystal under an irradiated region.