JPH01289184A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent crystal defects in the vicinity of a re-grown interface for obtaining a laser device longer in service life and higher in reliability by a method wherein meltback is effected, just before the second epitaxial growth process, for the removal of a part of a P-type GaAs active Iayer and of an N-type GaAs current stopping Iayer oxidized in a stripe shape trench forming process. CONSTITUTION:In the first epitaxial growth process, an N-type GaAs layer 2, an N-type AlGaAs first clad Iayer 3, a P-type AlGaAs active layer 4, a P-type AlGaAs second clad layer 5, a P-type GaAs active Iayer 6, an N-type AlGaAs etching stopper layer 7, and an N-type GaAs current stopping layer 8 are formed, in that order, all on an N-type GaAs substrate 1. A process follows wherein a P-type Al GaAs third clad layer 9 and a P-type GaAs contact layer 10 are deposited and made to grow by liquid phase epitaxy on the N-type GaAs current stopping layer 8, which is accomplished just after the removal in a meltback process of the surfaces exposed in the trench 11, which surfaces were oxidized when a trench 11 was provided, of the P-type GaAs active layer 6 and of the N-type GaAs current stopping Iayer 8. This method prevents the generation of a deep Ievel attributable to crystal defects.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor laser device, and particularly to a method for manufacturing a semiconductor laser device with small manufacturing variations and high reliability.

[Conventional technology]

FIG. 3 is a cross-sectional view showing the structure of a conventional so-called SAS type semiconductor laser device. In the figure, 1 is an n-type (hereinafter abbreviated as n-) GaAs substrate, and 2 is an n- GaAs buffer layer, 3 n AIQ, 4SGa provided on the butts yiiZ 6. SSA s first kraft layer 4 is a p-type (
(hereinafter abbreviated as p-) Alo, +5Gao, 5sA3 active layer, 5 is pA lo, asG provided on the active layer 4
a a, s5A s second cladding layer, 8 is an n-GaAs current blocking layer provided on the second cladding layer 5 and has a stripe-shaped groove 11 reaching the second cladding layer 5; 9 is a current blocking layer; pA 10.4SG ao provided so as to embed the striped groove portion 11 on the blocking N8,
ssA S third cladding layer, 10 is third craft layer 9
A p-GaAs contact layer provided above.

Further, FIG. 4 (al) and FIG. 4 (bl) are diagrams showing a conventional method for manufacturing a semiconductor laser device.

Next, the operation will be explained.

When a bias is applied between the p-GaAs contact layer 10 and the n-GaAs substrate I so that the p-GaAs contact layer 10 becomes positive, the region where the n-GaAs current blocking layer 8 is interposed between them, i.e. In the region where there is no striped groove 11, no current flows because a pnpn silicon risk structure is formed, and the current does not flow in the n-Ga
A current selectively flows only in the region where the As current blocking N8 is not present, that is, the region where the striped groove portion 11 is present. Reference numeral 12 in FIG. 3 indicates the path of the flowing current.

Electrons and holes injected into the active layer 4 due to the flow of current recombine and radiate light.

As the current increases, induced radiation eventually begins, leading to laser oscillation. The laser beam is p-
A 1 o, +sG a o, esA S active layer 4
and n −A 1 o, asG a o, ssA
S first craft layer 3. nA I 11.4SG a
o, SSA 5 2nd Cla Nodo N5 and nA 1
o, as Ga o, 15 As due to the real refractive index difference between the third Kraft layer 9 and the laser beam being absorbed by the n-GaAs current blocking layer 8 in the lateral direction of the device. The wave is guided by the index difference.

Next, a conventional method for manufacturing a laser device will be described.

First, in the first epitaxial growth, the n-GaAs base V
n-GaAs buffer layer 2 on the il. n-A Io,a
sGao, 5sAS first cladding layer 3. p-A1.1.
Ga, 1. xAs active layer 4.1) Alo, 4sGa
A second cladding layer 5 of o.5sAs and a current blocking layer 8 of n-GaAs are sequentially epitaxially grown to obtain the wafer shown in FIG. 4(a). At this time, the epitaxial growth method is not particularly specified, but an organic metal thermal decomposition method (hereinafter abbreviated as MOCVD method), which allows good controllability of the thickness of the grown layer, is generally often used. Next, a photoresist pattern 13 having stripe-like openings is formed on the wafer shown in FIG. 4(a) by photolithography. Next, the etching rate of GaAs is AI. , 4SG 86.55A Using an etching solution sufficiently larger than that of 3, specifically, a mixture of aqueous ammonia and hydrogen peroxide, only the n-1caAs current blocking N8 is selectively etched away to form a striped pattern. Grooves 11 are formed to obtain the wafer shown in FIG. 4(b). After removing the photoresist pattern 13, p Alo, 4sGao, ss
A! 1. A third gland N9 and a p-GaAs contact layer 10 are epitaxially grown in sequence, and the semiconductor laser device shown in FIG. 3 is completed. In this second epitaxial growth, pA lo inside the striped groove 11,
asG ao, ssA sSince it is necessary to perform epitaxial growth on the second cladding N5, MO
CVD method is used.

Depending on liquid phase epitaxy (LPE) or molecular beam epitaxial growth (MBE), AlG with a large At molar ratio can be
Since it is difficult to obtain a good epitaxial layer on aAs,
These growth methods are not suitable for this second epitaxial growth.

[Problem to be solved by the invention]

Since the conventional method for manufacturing a semiconductor laser device is configured as described above, the interface nodule @14 indicated by the X mark in FIG.
However, this becomes an oxidized so-called regrowth interface that is exposed to the outside air between the first epitaxial growth and the second epitaxial growth. Among the regrowth interfaces 14, the interface between the second cladding layer 5 and the third craft JW9 is made of AlGaAs, and is particularly oxidized. Layers grown epitaxially on oxidized wafers contain various crystal defects therein. Such crystal defects are particularly common near the regrowth interface. The vicinity of the regrowth interface 14 of the striped groove portion 11 contains many crystal defects for the above-mentioned reason. Many of these crystal defects constitute deep levels. When a semiconductor laser device manufactured using conventional manufacturing methods is driven, a portion of the laser light is absorbed into deep levels caused by crystal defects such as those mentioned above and is converted into heat, or injected carriers are absorbed into deep levels caused by crystal defects such as those described above. It is trapped in the active layer 4 and converted into heat, and the temperature near the active layer 4 increases. An increase in temperature near the active N4 causes an increase in the level of injection current necessary for laser oscillation, leading to a further temperature increase. In addition to the temperature rise cycle described above, due to an increase in crystal defect density due to temperature rise, etc., the semiconductor laser device manufactured by the conventional manufacturing method shown in Fig. 3 can output a constant output in a short period of time when the device is continuously energized. However, there is a problem in that the drive current increases to obtain the required voltage, and the oscillation eventually stops, resulting in a short life.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a semiconductor laser device that can manufacture a semiconductor laser device with a long life and high reliability.

Means for Solving Problem C] A method for manufacturing a semiconductor laser device according to the present invention includes a method for manufacturing a semiconductor laser device according to the present invention, in which Ga-Al-As
The p-type G in the striped grooves is selectively removed by the system melt.
A part of the aAs buffer layer and the n-type GaAst flow blocking layer is melt-banked, and then a p-type Alx Gal-8As third cladding layer and a p-type GaAs contact layer are sequentially formed in the same device. It is epitaxially grown using a liquid phase growth method.

[Effect]

In this invention, p-type GaA38777 in the striped grooves is selectively removed by a Ga-Al-As melt.
layer and a portion of the n-type GaAs current blocking layer, followed by successive p-type A1. Ga,
- Since the 8As third ground layer and the p-type GaAs contact layer are epitaxially grown sequentially by liquid phase growth, the regrowth interface does not come into contact with the atmosphere and oxidize, which prevents oxidation from occurring due to crystal defects near the regrowth interface. Since no deep level is formed, a highly reliable semiconductor laser device can be manufactured.

〔Example〕

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

FIG. 1 is a cross-sectional view showing the structure of a semiconductor laser device manufactured by a manufacturing method according to an embodiment of the present invention. In the figure, l is an n-GaAs substrate, 2 is an n-GaAs8
771 layers, 3 is n AIG, 4SG ao, ssA
S first ground layer, 4 is p Alo, +sGa, 1
．． As active layer, 5 is p A 1 a, 4sG a o
, 5sAs second cladding layer, 6 p-GaAs buffer layer, 7 n-A 1 o, asG ao, ss
A S etching stopper layer, 8 an n-GaAs current blocking layer, 11 pA 1 o, asG ao, ss
p-GaAs so that the second cladding layer 5 is exposed.
Buffer layer 6. n-A1 o, 4sG ao, s
sA 3-piece fitting stopper layer 7. The stripe-shaped groove part 9 is formed in the n-GaAs current blocking N8, and the p-A is formed so as to bury the stripe-shaped groove part 11.
10 is a p-GaAs contact layer; 10 is a p-GaAs contact layer; Also, the second
FIG. 2(a) to FIG. 2(d) are diagrams showing the manufacturing method according to this embodiment.

Next, the manufacturing method will be explained.

First, in the first epitaxial growth, an rt-GaA98771 layer 2*nA 1o, 4sGao, siA S first ground layer 3. p-A1o, l5Gao, m5AS active layer 4+ p-A 1a, aiGao, s5A 3
Second kraft layer 5゜p-GaAs buffer layer 6, n
Alo, 1sGao, 5iAs processing stopper layer7. An n-GaAs1i flow blocking layer 8 is successively epitaxially grown to obtain the wafer shown in FIG. 2(a). The reason why the MOCVD method was adopted as the epitaxial growth method here is that compared to the LPE method that is generally used for manufacturing semiconductor lasers, the MOCVD method is more effective at improving the internal distribution of the composition of the epitaxial layer, the distribution between batches, the internal distribution of the epitaxial layer thickness, and the batch-to-batch distribution. The average distribution, etc. is extremely small (standard deviation is approximately 1/1
2 (a) using photolithography technology.
) A photoresist pattern 13 having stripe-shaped openings is formed on a shrimp wafer, and this is used as an etching mask. A 1 o
, asG ao, ssA A striped groove portion 11a reaching the three-cutting stopper layer 7 is formed, and a second
The wafer shown in Figure ('b) is obtained. By immersing the wafer from which the photoresist pattern 13 has been removed in an aqueous solution of iodine and potassium iodide or an aqueous solution of hydrofluoric acid, the nA present at the bottom of the striped groove 11a is removed.
16,4sGao, 5sAs etching stopper N7 is selectively etched away, and p-GaAs is added to the bottom.
The striped grooves 11b of the buffer layer 6 are formed to obtain the wafer shown in FIG. 2(C).
Insert the wafer shown in C) into an LPE device (not shown),
By bringing the wafer into contact with the Ga-Al-As melt, the p-caAs buffer layer 6 existing on the top of the n-GaAs1i flow blocking layer 8 and the bottom of the striped groove 11b is melted back, and the p- A 1 o, asG
ao, ssA Striped grooves 11C exposed in the second cladding layer 5 are formed to obtain the wafer shown in FIG. 2(d). Following this step, p A 1 o, asG a o, 5sAs
By epitaxially growing the third cladding layer 9 and the p-GaAs contact layer 10 in sequence, the semiconductor laser device shown in FIG. 1 is completed.

Next, the operation of the semiconductor laser device shown in FIG. 1 manufactured by the manufacturing method of this embodiment will be explained.

When a bias is applied between the p-GaAs contact 7110 and the n-GaAS substrate 1 so that the p-GaAs contact JILO becomes positive, n-
Since a pnpn thyristor structure is formed in the region where the GaAs current blocking layer 8 is interposed, that is, the region where the striped groove portion 11 is not present, no current flows, and the n-GaA
Current selectively flows only in the striped groove portions 11 from which the current blocking layer 8 has been removed. The current path is schematically shown at 12 in FIG. Electrons and holes injected into the active layer 4 as a result of current flowing in this manner recombine and radiate light. As the injected current increases, induced radiation eventually begins, leading to laser oscillation.

The laser beam is p-At in the vertical direction of the device. , 1°Ga
o, 5sAS active layer 4 and n-A 1o, 443Ga@
, 51As first cladding layer 3. n-A1o, asGao
, 5s AS second cladding layer 5 and n A 16.4S
Due to the real refractive index difference between G a @, 5SA3 and the third cladding layer 9, the laser beam becomes p- in the lateral direction of the device.
GaAs buffer layer 6 and n-GaAs1i flow blocking layer 8
The wave is guided by the refractive index difference caused by absorption by the

As described above, in the semiconductor laser device manufactured by the manufacturing method of this embodiment, the oxidized pCl was removed in the step of forming the stripe-shaped groove portion 11b immediately before the second epitaxial growth.
- Since part of the GaAs buffer layer 6 and f'1-GaA3 current blocking layer 8 is removed by meltback, deep levels due to crystal defects are not introduced near the regrowth interface, resulting in a long life and high stability. A semiconductor laser device can be obtained. In addition, p-GaAs buffer y from which meltback is removed
N6 is pA l 11+ 41cao, ssA
s second cladding layer 5 and pA l (1,4SG a
o, ssA Since it has the same electrical conductivity type as the S third cladding layer 9, the p-GaAs buffer layer 6 may remain slightly after melting back, or the p-GaAs buffer layer 6 may be completely melted back. However, even if the dopant remains at the interface, it does not cause deterioration of the electrical characteristics such as an increase in the series resistance of the device.

In the above embodiment, MOCVD was used as the first epitaxial growth method, but it goes without saying that other methods such as MBE or LPE may be used.

〔Effect of the invention〕

As described above, according to the present invention, a part of the n-GaAs current blocking layer and the p-GaAs buffer layer inside the striped groove are selectively grown using the Ga-Al-As melt in the liquid layer epitaxial growth apparatus. melt back,
Subsequently, p-AIX Ga+-w A in the same device
Since the third cladding layer and the p-GaAs contact layer are epitaxially grown sequentially by the LPE method, a semiconductor laser device with long life, high reliability, and good electrical characteristics such as series resistance of the device can be obtained. It has the effect of being

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a semiconductor laser device manufactured by a method for manufacturing a semiconductor laser device according to an embodiment of the present invention, and FIGS. Diagram 3 showing the manufacturing method of the laser device
The figure is a cross-sectional view showing a semiconductor laser device manufactured by a conventional method for manufacturing a semiconductor laser device, and FIGS. 1 is an n-GaAs substrate, 2 is an n-GaAs buffer layer,
3 is n A lo, asG a o, 55A
a first cladding layer, 4 p-A la, +sG a
o, ssA s active layer, 5 is p -A l 1),
45G ao, ssA s second cladding layer, 6 p-GaAs buffer layer, 7 n-Alo, 4sG a
6.55 A s etching stiffness layer, 8 is n-G
aAst flow blocking layer, 9 is pA 1 o, asG a
o, 5a AS third cladding layer, 10 a p-GaAs contact layer, 11 a striped trench. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An n-type GaAs buffer layer on an n-type GaAs substrate,
n-type Al_xGa_1_-_xAs first cladding layer, n
type or intrinsic or p-type Al_yGa_1_-_
yAs (y<x) active layer, p-type Al_xGa_1_-_
A first step of sequentially epitaxially growing an xAs second cladding layer, a p-type GaAs buffer layer, an etching stopper layer of n-type Al_zGa_1_-_zAs (z>0.40), and an n-type GaAs current blocking layer; The above n-type G is
aA3 current blocking layer with n-type Al_zGa_1_-_zAs
A second step of forming striped grooves reaching the etching stopper layer; and Al_zG in the striped grooves using an aqueous solution of iodine and potassium iodide or an aqueous solution of hydrofluoric acid.
a_1_-_zThe third step of removing the As etching stopper layer and the step of removing the Ga-Al-
a fourth step of selectively melting back a part of the p-type GaAs buffer layer and the n-type GaAs current blocking layer in the striped grooves with an As-based melt; p-type Al in the device
_xGa_1_-_xAs third cladding layer and p-type Ga
A method for manufacturing a semiconductor laser device, comprising: a fifth step of sequentially epitaxially growing an As contact layer by a liquid phase growth method.