JPS59132185A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve productivity and to enhance a yield rate, by a first liquid phase epitaxial growing process, an etching process, a process, by which a second liquid phase epitaxial growing is performed in the etched region, and a third liquid phase epitaxial growing process. CONSTITUTION:On an N type GaAs substrate 9, the following layers are formed by epitaxial growth: an N type Al0.3Ga0.7As clad layer 1; an N type Al0.1Ga0.9As light guiding layer 2; an Al0.03Ga0.97As active layer 3; and a P type Al0.3Ga0.7As clad layer 4. Then, the semiconductor layers 1-4 are made to remain in stripe shapes by etching. Then, a P type Al0.3Ga0.7As layer 5 and an N type Al0.3Ga0.7 As layer 6 are provided by the epitaxial growth. An oxide layer 14 is formed on the layer 4. Then, a P type Al0.3Ga0.7As layer 7 and a P type GaAs layer 8 are sequentially formed by a liquid phase epitaxial growth.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor laser having a buried heterostructure.

In general (in semiconductor lasers, buried type semiconductor lasers have appeared in order to realize low oscillation threshold current and stable fundamental mode oscillation.The structure of this semiconductor laser is as follows.
The active layer region is complementarily surrounded by a low refractive index material.
, for example, in the case of a Ga As active layer, λ/2 ()
It is surrounded by the a A s layer and has a strong optical waveguide effect. As a result, this semiconductor laser has a low threshold and a considerable development power, but on the other hand, the difference in refractive index between the active layer region and the surrounding low refractive index material becomes larger than necessary. Therefore, the stripe width is 1μ
Fundamental mode oscillation occurs within m m, but when the stripe width becomes wider than that, it becomes unavoidable that higher-order modes are mixed in. Also, if the stripe width is narrow, the optical output naturally decreases to f, l m. Although it is limited to W or less, there is a drawback that the optical output is too small.

In order to improve these drawbacks of the buried semiconductor laser, an optical waveguide-enclosed buried semiconductor laser has been proposed in which an optical waveguide layer is provided under the active layer. In this optical waveguide encapsulation structure, an optical waveguide layer is provided separately from the active layer, and the light from the active layer is propagated to the optical waveguide layer to obtain a large optical output.

The construction and manufacturing method of a conventional optical waveguide-sealed embedded semiconductor laser will be explained with reference to FIG. UMJ.

Figure 1 shows this conventional structure (1+j), and Figures 2 (, l) to (c) show the manufacturing process shown in Figure 1.
This is a Tfi plane view.

First, as shown in Figure 2<2), n-type C+ a A
n-type A4.3 Ga64 As cladding layer 1, n qA l, , G'ao, As light wave layer 2 on s substrate 9
A4°, 83 Gao, g7 AS active layer 3, P type A7o, 3Ga. , 7As cladding layer 4 is sequentially formed by a first liquid phase epitaxial growth process. Then the second
Figure (b) ζAs shown, a striped mask is provided on the cladding 1 and the semiconductor layer 1.2.3.4 is selectively etched to a depth that reaches the GaAs substrate 9.
is left in a stripe pattern. Next, the etching mask is removed and the crystal surface is cleaned, but since the AI composition ratio of this layer is high, an oxide layer 11 is naturally formed on the surface of the cladding layer 4 due to a chemical reaction with oxygen in the air, etc. . After that, a second liquid phase phase formation process is performed to form P-type Alo3Ga.
o7As layer 5, n-type An(,,Ga,), tAs layer 6
are sequentially provided, but since no crystal grows on the oxide M11, the oxide layer 11 becomes a selective crystal growth mask, and the semiconductor layer is formed only in the regions on both sides of the stripe (the second
(c) ). These semiconductor layers 5.6 are current blocking layers. After the second liquid phase epitaxial growth step, when this laser crystal is exposed to the atmosphere, n-type A 11 o, 3 Ga
(,,,, An oxide film 10 is naturally formed on the surface of the As layer 6. This oxide layer 11 is selectively removed, and the P electrode 12
, and the n-electrode 13 are formed to complete the optical waveguide-embedded semiconductor laser shown in FIG.

In this structure, the oscillated light spreads and propagates from the active layer to the optical waveguide layer, so the light intensity within the active layer does not increase much, and even if the light is output in a light-controlled manner, it can operate without causing optical damage to the active layer. can.

Furthermore, since the light propagation region is surrounded by a semiconductor layer having a lower refractive index than this region, stable fundamental mode oscillation is possible. In addition, current blocking layers are formed on both sides of the striped current injection region to achieve low-frequency oscillation. However, since no crystal grows on the oxide J-11, the n-type A7,3Ga , 3? As rs 6 grows upward or downward relative to the cladding layer 4 (compared to the cladding layer 4), and since the amount of upward or downward growth cannot be controlled, unevenness occurs on the crystal surface on the P electrode side, resulting in The P electrode also has irregularities.In a semiconductor laser, one pole (in this case, the P electrode) close to the active layer is densely layered on a heat sink to dissipate heat, but this type of semiconductor Since the electrodes of lasers are not flat, the heat sink is not flat, and the efficiency of heat dissipation is low.
The unevenness of the electrodes is not constant, which causes problems (the temperature customization of this element varies), and the unevenness of the crystal surface on the P'749 pole side makes the PEW formation process and device fabrication difficult, which reduces the yield. impeding improvement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a buried semiconductor laser which eliminates the above-mentioned drawbacks of the conventional manufacturing method and has good productivity and yield.

The semiconductor laser manufacturing method of the present invention includes first and second semiconductor cladding layers having a lower refractive index than that of the semiconductor active layer on both surfaces of the semiconductor active layer and in contact with the semiconductor active layer. a first liquid phase epitaxial growth process for forming a multi-M structure on a semiconductor substrate; an etching process for selectively etching from a second semiconductor cladding layer of BIJ to a depth reaching the semi-conductive substrate; and the etching region. A second liquid phase epitaxial growth step for forming a single or plural third semiconductors having a refractive index lower than that of the semiconductor active layer, and a second liquid phase epitaxial growth step in which the standard redox potential is negative and its absolute value is a cleaning step of cleaning and removing an oxide film on the surface of the second semiconductor layer using a solution containing one or more elements, and a single or plural fourth semiconductor layer in contact with the second and third semiconductor layers. and a third liquid phase epitaxial growth step for forming a semiconductor layer.

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 3 is a sectional view showing the embodiment of the present invention, and Fig. 4 is a sectional view showing the manufacturing process of this embodiment. Iti of (a) to (c)
'a process is W2 diagram (a), (b) 0) explanation and %
The explanation is the same as the first half of 2 IA(c), except that the oxide layer 11 in FIG. 2 is shown as the oxide layer 14 in FIG. P 41'A7o, 3G'a, 7A
s layer 5, n4pA11. ．． After forming 3Gao, 7As@6 on both horizontal sides of the stripe region, n-type Al
, ), 3Ga, 37As). The oxide layer 14 is removed by a cleaning solution placed between the solution used to grow the layers and the solution used to grow the next layer.

This cleaning solution is P-type AA'. , 3 Ga(1,7
' A 31) Growth of ji 5 (having a composition similar to the solution used and containing special violet substances such as Al, Mg, and Be whose standard oxidation attainment point (hereinafter referred to as "E") is negative) It has the function of removing the oxide layer.

After this, by the second latter half of liquid phase epitaxial growth, P
3JAAlo, Gao, 7As layer 7, P type Ga
A sA IJ O, 3G a 6.7 A 8 layer 7,
If the layer thickness of P-type GaAs J78 is made sufficiently large, then P-type A lo, 3 Ga6.7 As J@4 and n-type A
Even if there is a step between AssGa, lo, 30a, and AssGa, the surface of the P-type GaAs layer 8 is flat.

In this way, one crystal has 12 P' poles and n' ton poles]
3 is completed to complete the buried semiconductor laser.

In this case, the typical layer thickness is the n-type Ga As substrate 9
Step difference: 0.3μm, n%A 16.3Ga o4
A s ) 匈1 is 1 μm.

n 1gjA lo, I Ga 6. g A s ) f
42 is 0.5 μm, active No. 3 is 0.1 μm, p-type A1
0.3 Ga o, 7 As) 74 is 0.5 μm, PiJj
l A 7 o, 3 G a o, 7 A S Layer 5 is 1.511 m, n WAA! o, sGa. , 7As
146 is 1 μm, P type A It o, s Ga. ,y
As1tJ7 is 1μm, P-type GaAs layer 8 is 1μm.
m.

According to the manufacturing process of the present invention, when forming current blocking layers on both sides of the stripe region, the oxide layer 14 prevents crystal growth on the P-type AIJo, sGaO-?AsHa 4. Furthermore, after forming the current blocking layer, an epitaxial layer can be formed on the entire surface of the crystal by removing the oxide layer with a cleaning solution.

Although the selective crystal growth mask used here is a naturally formed surface oxidation layer, it may also be an actively formed surface oxidation layer. Furthermore, the elements such as A11Mg and Be contained in the cleaning solution used in this example are sufficiently effective even in the case of slight ruts.

In addition, the smaller the Eo value of these elements, the more likely the reduction reaction occurs, and the greater the effect, but EoIM
When is larger than -1, the effect of non-invention cannot be expected much. Chinami ζko AI! , M g , and Be, Mg (E, = -2,363> has the largest effect, followed by Be (-1,85) and Al (-1,
662).

According to the implementation of the present invention, since the laser crystal surface is flat, the electrode near the active layer can be formed flat, and this electrode can be used as a heat sink to improve heat dissipation efficiency. . Furthermore, since the electrodes can be felt over the entire surface of the laser crystal, the improvement in heat dissipation efficiency is even more remarkable.

Furthermore, the flatness of the surface facilitates the electrode formation process and digitization, thereby improving the manufacturing yield.

As described in detail above, the manufacturing method of the present invention enables stable zero-order mode oscillation with a low oscillation threshold current and high optical output, and also provides high heat dissipation efficiency. A semiconductor laser can be provided. In addition, since a flat crystal surface can be formed, it becomes easier to form electrodes and fix the device during electrification, which improves yield and eliminates distortion during device fixation, resulting in a highly reliable semiconductor laser. be able to.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional embedded semiconductor laser;
Figures (a) to (C) show the method in Figure 1 in order of process.
Figure 3 is a top view of one embodiment of the present invention;
Figures (a) to (d) are cross-sectional views showing the manufacturing method of an embodiment of the present invention in the order of steps. In the figure, 1.6... n-type A lo, s Ga o,...
As layer, 2--n FJA lo, tGa,),
g As7, 41.3°°゛・°°active active layer 4,
'5, 7-...-P type A11o, Gao, 7As
Layer, 8... P-type Ga As layer, 9--n
5G: 4A s substrate, 10--n5A l
(,,3Gao,7,AsB1 layer,11--P
i'd -A lO,3GaO17As oxide layer, 1
2...P electrode, 13...-n electrode, 14
...P type AA. , 3 G a O',?
This is an AS surface metamorphic layer. Figure 1 (b”) Figure 3 (α) (C) (d)

Claims (1)

[Claims] First liquid phase epitaxial growth for forming on a semiconductor substrate a semiconductor multilayer structure having at least first and second semiconductor cladding layers having a lower refractive index than the semiconductor active layer on both sides of the semiconductor active layer and in contact with the semiconductor active layer. process and
an etching step of selectively etching to a depth that reaches the semiconductor substrate from the second semiconductor cladding layer; and a single or plural third etching layer having a refractive index lower than that of the semiconductor active layer in the etching region. cleaning the oxide film on the surface of the second semiconductor layer using a second solution that forms a semiconductor layer; an epitaxial growth process; and a solution containing an element whose standard redox potential is negative and whose absolute value is 1 or more; and a third liquid phase epitaxial growth step of forming a single or plural fourth semiconductors W in contact with the second and third semiconductor layers. Production method.