JPH01304793A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To increase a crystallinity of a regrowing interface by forming a cap layer by a method wherein the cap layer is allowed to start growing with a GaAs etching stopper layer left behind and during the growth of the layer an upper clad layer is exposed by melting back the GaAs etching stopper layer. CONSTITUTION:The thicknesses d1-d5 of a GaAs etching stopper layer 10, an AlGaAs etching stopper layer 11, a current block layer 5, an anti-meltback layer 12 and a meltback layer 13 are on the following conditions: 0<d1<=0.3mum, 0<d2<=0.3mum, 0.3mum<=d3<=2mum, 0.1mum<=d4<=0.4mum and 0.1mum<=d5<=0.4mum. With the GaAs layer 10 for oxidation prevention left behind thinly at the bottom of a ditch formed on the current block layer 5 as a current path and an upper clad layer 4 not exposed to air, a cap layer 7 is formed by a method wherein the cap layer is melt back by the liquid phase epitaxial method at the time of growing and only the GaAs layer 10 for oxidation prevention is removed. By this method, a high crystallinity can be obtained at a regrowing interface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing an m-v group compound semiconductor laser device.

[Conventional technology]

FIG. 2 is a cross-sectional view showing a semiconductor laser device manufactured by a conventional manufacturing method, and in the figure, 1 is, for example, S
An n-type GaAs semiconductor substrate doped with a donor such as 1 at a high concentration; 2 is an n-type A semiconductor substrate 1 formed on the semiconductor substrate 1 by a method such as MO-CVD; G a, -, A
s upper cladding layer, 3 is A grown on the lower cladding N2
I, G a + -y As active layer, 4 is the lower cladding layer 2. P-type A 1 doped with an acceptor such as Zn, forming a double heterojunction with the active layer 3
g Ga +-++ As upper cladding layer; 5 is an n-type GaAs current blocking layer grown on the upper cladding layer 4; 6 is a current path trench formed in a stripe shape in the current blocking layer 5; 7 is a P-type At which is grown by a method such as MOCVD in order to electrically contact the upper cladding N4 in the groove 6 for the current path on the current block N5.
□Ga+-gAs cap layer, 8 is a P-type contact layer grown sequentially on the cap layer 7, 9a and 9b are the above-mentioned contacts, respectively) ii8. This is an electrode mainly made of, for example, AuGe, Ni, or Au, which makes ohmic contact with the semiconductor substrate 1.

Next, the operation will be explained.

If a forward voltage is applied between electrodes 9a and 9b, active N3
A forward electric field is generated in the PN junction including the PN junction, and a current flows. At this time, the current selectively flows through the current path groove 6 due to the depletion layer formed between the block layer 5 and the upper cladding layer 4, causing local current injection into the active layer 3, and , lower cladding [2° active layer 3. The double heterojunction formed with the upper cladding N4 causes population inversion of the injected carriers, stimulated emission of photons, and causes laser oscillation.

Further, a current blocking layer 5 for light seeping out from the active layer 3
The transverse mode is stable due to the effective refractive index distribution in the transverse direction caused by the difference in the amount of light absorbed by the cap 7I7 and the cap 7I7.
Laser oscillation characteristics with fewer kinks can be obtained.

Next, the manufacturing method will be explained.

First, in a first epitaxial growth step, a lower craft layer 2. Active layer 3. Upper cladding layer 4. current block 1i
5 are stacked one after another. Next, a striped current passage groove 6 exposing the upper cladding II 4 is formed in the current blocking layer 5, and then a second epitaxial growth process is performed to form the current blocking layer 5 and the current passage groove. A camp layer 7 and a contact layer 8 are sequentially laminated on 6. Then, electrodes 9a and 9b are formed in ohmic contact with semiconductor substrate 1 and contact layer 8, respectively, to complete the device.

[Problem to be solved by the invention]

Since the conventional method for manufacturing a semiconductor laser device is configured as described above, the upper craft layer is exposed at the bottom of the current path groove before the second epitaxial growth,
This part is oxidized, and due to the influence of this oxidation, there is a restriction that in order to grow the cap layer in the second epitaxial growth process, it cannot be grown unless a vapor phase growth method such as MOCVD is used. Even if the second epitaxial growth can be performed using the method described above, the oxide layer of the above-mentioned upper craft layer may exist in the interface or cause deterioration of crystallinity. The problem is that crystal defects occur due to the absorption of energy, that is, the absorption of photons, and the generation of heat spots, resulting in poor reliability.

This invention was made to solve the above-mentioned problems, and it is possible to prevent oxidation of the regrowth interface in the second epitaxial step, and to provide a highly reliable semiconductor laser device with improved crystallinity. It is an object of the present invention to provide a method for manufacturing a semiconductor laser device that can be manufactured at a low yield and at low cost.

[Means to solve the problem]

In the method for manufacturing a semiconductor laser device according to the present invention, AlxGal-
w A s AC 5 hood layer + AI, Gap-, A! 1 active layer, Aim Gap-g As upper cladding layer, Ga
A S engineering 7 Chingstukhva layer, A 1 r G
a + - r A s (r≧0.4) etching stopper layer, GaAs current blocking layer, first conductivity type A I ,
G a 1. -, As (p≧0.4) anti-meltback layer + GaAs meltback layer are grown sequentially, and a selective etchant selective to GaAs and a selective etchant selective to AlGaAs are alternately grown. Using the above meltback layer, anti-meltback layer, current block 15. A stripe-shaped groove is formed by processing to penetrate each layer of the AlGaAs etching stopper layer, and the GaAs etching stopper layer exposed at the bottom of the stripe-shaped groove is melted back in a crystal growth apparatus to form the upper craft. A1. layer is exposed, followed by A1. A Ga, mAs cap layer is laminated by liquid phase epitaxy so that the main surface is flat.

[Effect]

In this invention, a GaAs layer for preventing oxidation is left in the form of a thin film at the bottom of the current path groove formed in the current blocking layer grown in the first epitaxial growth step, and the upper cladding layer is exposed to the atmosphere. Since the next cap layer is melted back during growth using the liquid phase epitaxial method and only the GaAs layer for preventing oxidation is removed, the crystallinity at the regrowth interface is improved. A highly reliable semiconductor laser device can be obtained.

〔Example〕

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

FIG. 1 is a cross-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. In the figure, the same reference numerals as in FIG. Type Al, Ga, -
, ASz etching stopper layer, 12 is current blocking layer 5
The n-type Al, Ga, -, As anti-meltback layer 13 laminated thereon is an n-type GaAs meltback layer laminated on the anti-meltback layer 12 .

6 is a GaAs etching stopper layer 10. AlGaAs
Etching stopper! j11. Flow block layer 5. Anti-meltback layer 12. The current path grooves 7 formed in the meltback layer 13 are P-type Al@Ga formed by liquid phase epitaxial method so that the main surface is flat.
This is a p-++ As cap layer.

Next, the manufacturing process will be explained.

First, in the first epitaxial growth step, n-type Ga
On the As substrate 1, 1) n-type AIX Ga, -, AI lower cladding 92° 2)
Aly Gap-y As active layer 3゜3) P type A 1
@G a l-m A S upper cladding layer 4゜4) P-type GaAs etching stopper N10゜5) n-type Al, G
a, -, As (r≧0.4) Etching stopper layer 1
1゜6) N-type GaAs current flow layer 5゜7) N-type At, Ga1-p As (p≧0.4) anti-meltback layer 12. and 8) sequentially grow an n-type GaAs melt buffer layer 13. Here, the GaAs etching stopper Fil O, the AlGaAs etching stopper layer 1
1. Flow block layer 5. Anti-meltback layer 12. The thickness of each layer of the meltback layer 13 d1+ di, ds,
d4+ a, is 0<d, ≦0.3 μm.

Q<d2≦0.3 μm.

0.3. czm≦d, ≦2pm.

0.1 μm≦d4≦0.4 μm+ 0.1, c+m5d, ≦0.4 μm.

By setting the thickness of each layer to the above values, a desired laser structure can be easily obtained.

Next, a method of forming the groove 6 for the current path will be described.

Melt bank layer 13. The soil component of the current block layer 5 is Ga
As the etchant used for forming the groove, for example, NHa OH: Hz Ox -1=30.1
0°C, tartaric acid:HtO□=5:1°20°C, etc., and is hereinafter referred to as GaAs etchant. These G
The aAs etchant has a characteristic that the etch rate of AltGa and As (l≧0.4) is about two orders of magnitude lower than that of GaAS. Also A
lp Gat-p A” Anti-meltback l!12.
The main component of the Air Ga1-r As etching stopper layer 11 is A170al-7AS, and the etchant used for groove formation is, for example, KI:Jz:H□
0-345:195:300 (weight ratio), RT, etc., and these AtGaAs etchants, hereinafter referred to as AlGaAs etchants, are AIJGa+-tAs.
For an etch rate of (ffi≧0.4), GaA
It has the characteristic that the etch rate of s is about two orders of magnitude smaller.

In the laser structure of this example, E≧0.4, that is, p≧0°4
, r≧0.4, it becomes possible to sequentially and selectively etch the above-mentioned epitaxial layer using the above-mentioned etchant. That is, meltback layer 1
After photoengraving stripes on 13.3, these meltback layers 13. Anti-meltback layer 12. Current blocking layer 5. By sequentially etching the four epitaxial layers of the AIGaAS etching stopper layer 11 using the above-mentioned GaAs etchant and A, lGaAs etchant in the order of GaAS etchant AIGaAs etchant-GaAs etchant-A and 1GaAs etchant. , very reproducibly, GaA
Etching for forming the groove 6 for the current path can be completed with the etching stopper 1110 remaining, that is, with the upper cladding layer 4 not exposed to the atmosphere.

Next, the cap layer 7 and the contact layer 8 are epitaxially grown using a liquid phase epitaxial growth method or the like on the wafer in which the current path grooves have been formed as described above. The GaAs etching stopper layer 10 left in the above-mentioned groove processing is melt-punctured by performing melt contact with the saturability of the layer slightly unsaturated and then lowering the growth temperature to grow the saturability in a saturable state. to expose the upper craft layer 4 during growth,
By growing the cap layer 7 thereon and subsequently growing the contact layer 8, the device of this embodiment can be obtained with good reproducibility.

A lx G a +-7A S (1≧0.4)
It is known that the meltback speed of GaAs is about 8 times lower than that of GaAs, so in this embodiment, an anti-meltback layer 12 with a large A1 molar ratio is provided to protect the current blocking layer 5. , this anti-meltback N1
A melt-back layer 13 is provided to prevent oxidation of 2.

Next, the operation will be explained.

Similarly to the conventional device, the semiconductor laser device manufactured by the manufacturing method of this example also oscillates in a stable transverse mode based on the same principle if a forward voltage is applied between the electrodes 9a and 9b. In this case, since the cap layer 7 was grown without exposing the upper cladding N4 to the atmosphere, the crystallinity of the regrowth interface is improved, and the absorption of light energy generated during laser operation, that is, absorption of photons, and heat spots are improved. Inconveniences such as an increase in crystal defects due to the occurrence of this do not occur.

In the above embodiment, the conductivity type of the semiconductor substrate 1 is n type, but it is assumed that the conductivity type of the semiconductor substrate 1 is n type.
Each semiconductor layer may also be of an opposite conductivity type.

〔Effect of the invention〕

As described above, in the method for manufacturing a semiconductor laser device according to the present invention, the growth of the cap layer is started with the GaAs etching stopper layer remaining, that is, the upper cladding layer is not exposed to the atmosphere, and the cap layer is grown. Ga inside
Since the As etching stopper layer is melted back to expose the upper cladding layer and the cap layer is grown on the upper cladding layer, the crystallinity of the re-grown interface is good and a highly reliable semiconductor laser device can be obtained. There are benefits to be gained.

[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 FIG. 2 is a sectional view showing a semiconductor laser device manufactured by a conventional manufacturing method. . 1 is a semiconductor substrate, 2 is a lower cladding layer, 3 is an active layer, 4 is an upper cladding layer, 5 is a current blocking layer, 6 is a groove for current passage, 7 is a cap layer, 8 is a contact layer, 9a and 9b are electrode, 10 is a GaAs etching stopper layer, 11 is A
12 is an anti-meltback layer, and 13 is a meltback layer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A first conductivity type Al_xGa_1_-_xAs lower cladding layer and an Al_yGa_1_-_yAs active layer on a first conductivity type GaAs substrate. A second conductivity type Al_xGa_1_-_xAs upper cladding layer, a second conductivity type GaAs etching stopper layer with a layer thickness d_1, a first conductivity type Al_rGa_1_-_rA with a layer thickness d_2
s etching stopper layer, first conductivity type GaAs current blocking layer with layer thickness d_3, first conductivity type Al_pGa_1_-_pA with layer thickness d_4
s anti-meltback layer and a GaAs meltback layer of the first conductivity type with a layer thickness d_5, where 0<d_1≦0.3μm 0<d_2≦0.3μm 0.3μm≦d_3≦2μm 0.1μm≦d_4≦ 0.4μm 0.1μm≦d_5≦0.4μm r≧0.4 p≧0.4 A first step of sequentially growing 0.4μm 0.1μm≦d_5≦0.4μm r≧0.4 p≧0.4 and a selective etchant that is selective to GaAs and AlG
A second method of processing and forming striped grooves penetrating each layer of the meltback layer, anti-meltback layer, current block layer, and AlGaAs etching stopper layer by alternately using a selective etchant that is selective to aAs. The GaAs etching stopper layer exposed at the bottom of the striped groove is melted back to expose the upper cladding layer in a crystal growth apparatus, and then the striped groove is grown in the same apparatus. and a third layer in which an Al_xGa_1_-_xAs cap layer of the second conductivity type is laminated on the melt-back layer by liquid phase epitaxy so that the main surface is flat.
A fourth step of laminating a second conductivity type GaAs contact layer on the cap layer, and a fifth step of forming ohmic electrodes on the GaAs substrate and the contact layer, respectively. A method for manufacturing a semiconductor laser device.