JPS62186580A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent the annulment of an internal stripe structure, by forming a groove right above a current blocking layer of multi-layer structure formed on a substrate possessing a ridge, and forming a double hetero-structure in the blocking layer containing the groove. CONSTITUTION:A ridge is formed on a GaAs substrate 1, and a current blocking layer 10 is formed thereon by epitaxial growth, wherein a plurality of GaAs layers having a conduction type inverse to the substrate and barrier layers are alternately formed. Using a photo mask, a central portion of the ridge in the blocking layer 10 is eliminated in the form of a stripe, which is used as a mask for etching to expose a part of the substrate 1. After that, a double hetero-structure is grown on the substrate surface, followed by the formations of a clad layer 4, an active layer 5, a clad layer 6 and a cap layer 7. In this manner, the annulment of an internal stripe structure can be prevented, even if the thickness and the carrier density of the current blocking layer disperse irregularly. Consequently, a laser device which operates with a small current and oscillates in a fundamental mode can be manufactured with high reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor laser device, which has been rapidly used as a light source for various electronic devices and optical devices and is in increasing demand in recent years. be.

(Prior Art) Important performances required of semiconductor lasers as coherent light sources for electronic and optical equipment include low current operation and fundamental transverse mode oscillation. In order to achieve these performances, the current flowing through the laser element is concentrated near the active region where the laser light propagates, suppressing its spread.
and needs to be confined. A semiconductor laser having such a structure is usually called a stripe type semiconductor laser, and one typical stripe type semiconductor laser is an internal striso type laser.

Below, with reference to the drawings, BTR8 (Buri
ed Twjn-Ridge 5ubstrate 5
The structure type laser will be explained.

Figure 4 shows the configuration of the BTR8 type laser, where 1 is a p-type GaAs substrate, 2 is an n-type GaAs current blocking layer, 4 is a p-type Ga1 yAtxAs cladding layer, and 5 is a Ga1
-yAlyA B active layer (0≦y<x), 6H,
n-type Ga1-XAtXAs cladding layer, 7 is n-type Ga
, As cap layer, 8 is p-side ohmic electrode, 9 is n
It is a side ohmic electrode.

The manufacturing method and operation of the BTR8 type laser configured as described above will be briefly described below.

The conventional BTR8 laser is formed using two liquid phase epitaxy (LPE) crystal growth steps.

First, an n-type GaAs current block 1F is placed on a p-type GaAs substrate 1.
The first crystal growth step is to form layer 2, and then 7-shaped grooves with internal stripe width W are formed by 7-otolithography. Then, a double heterostructure including an active layer 5 is formed thereon, and ohmic electrodes 8 and 9 are formed on the p side and the n side.
It is made by forming. Then, when voltage (g) is applied to the p-side electrode 8 and voltage (-) is applied to the n-side electrode 9, n-type GaA
s Current blocking layer 2. , only the p-n junction portion of the Thp type GaA mu S succinode layer 4 is applied with a voltage in the opposite direction, and the injected current flows only from the internal stripe width W.
The current concentrates directly on the active M5, and as a result, low current operation and fundamental transverse mode oscillation are realized.

(Problems to be Solved by the Invention) However, in the above internal stripe structure, the layer thickness and gearia concentration of the n-type GaAs current blocking layer 2 are 1
If there are variations in the individual laser elements or variations within the wafer surface, the n-type Ga
The diffusion distance of holes in the electron-hole pairs generated in the AT4 current blocking layer 2 is larger than the thickness of a part of the n-type GaAs current blocking layer 2, and the n-type GaAs The current blocking layer 2 is accumulated near the interface with the p-type substrate 1, and as a result, an internal stripe structure is formed.1. The barrier created by the p-n junction in the opposite direction, which had been maintained, is no longer active, and the internal stripe structure is lost.

Therefore, the operating frost flow value required to obtain the same light output increases, and the effective current stripe width also increases, resulting in an increase in the light emitting area in the active region, resulting in the problem of multimode oscillation. occurs. This phenomenon is considered to be due to the synergistic effect of the fact that the current blocking layer is a single layer and that the two crystal growths are both carried out in the liquid phase by the taggital method.

In view of the above problems, the present invention provides that even if the layer thickness and carrier concentration of the n-type GaAa current blocking layer 2 vary, the n-type GaAl
1. In the current blocking layer 2, holes in electron-hole pairs generated by light emission from the active layer 5 are effectively recombined with electrons,
The present invention provides a method for manufacturing a semiconductor laser device that can prevent the internal striso structure from expiring and can produce a semiconductor laser device that operates at low current and oscillates in a fundamental transverse mode with good reproducibility.

(Means for Solving the Problem) In order to solve the above problem, the method for manufacturing a semiconductor laser device of the present invention first includes forming a conductive type opposite to that of the substrate on a conductive substrate having a ridge. A first multilayer thin film consisting of three or more layers including at least one layer with a forbidden band width smaller than other layers is formed by an epitaxial method, and then, directly above the horn of the first multilayer thin film, A step of forming a groove reaching the conductive substrate from the surface thereof, and forming a second multilayer thin film having a double heterostructure including an active layer on the first multilayer thin film including the groove by liquid phase epitaxial method. It is something to be taken.

(Function) With this configuration, a semiconductor laser device having an internal stripe structure that operates at low current and oscillates in a fundamental transverse mode can be manufactured with high yield.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross section of a semiconductor laser device according to an embodiment of the present invention. In Figure 1, 1 is p-type GaAa
A substrate, 10 a current blocking layer made of a multilayer thin film, 4 a p-type C
5 is a GaAtAs active layer, 6 is an n-type GaAtAs cladding layer, 7 is an n-type GaAs cap layer, 8 is a p-side ohmic electrode, and 9 is an n-side ohmic electrode.

FIG. 2 is a diagram showing the manufacturing process of a semiconductor laser according to the present invention, in which 1 is a p-type GaAs substrate, 1o is a multilayer current blocking layer,
3 is a photoresist film. FIG. 3 shows a cross section of an example of a multilayer current blocking layer 1o, where 1 is a p-type G
aAs substrate, 2 is n-type GaAs layer, 11 is GaAtAs
The barrier layer 4 is a p-type layer aAtAs cladding layer.

Next, a specific manufacturing method will be explained. First, here, a p-type QaAs substrate is used as the substrate.

This p-type GaAs substrate 1 (carrier concentration) ~1019
On the (100) plane of cm -3), stripes with a width of 50 μm were formed using a photoresist film at a pitch of 250 μm in parallel to the <01> direction, and by chemical etching, a ridge with a height of 1.5 μm was formed. do. After cleaning the surface and removing the photoresist film, remove the p-type Ga with the ridge.
The metal organic vapor phase epitaxial growth method (hereinafter referred to as MOCV) allows easy growth of multilayer thin films on the As substrate 1 and has good layer thickness control.
(referred to as the D method), the thickness is 0.3μ as shown in Figure 3.
m n-type GaAs layer 2 (carrier concentration ~5 x 101
GaAtAs2 with a thickness of 005 μm and 3 layers of
Two layers of 97 layers 11 were epitaxially grown alternately, resulting in a total of 5 layers.
A multilayer current blocking layer 10 having a thickness of 1 μm is formed. An example of the crystal growth conditions at this time is that the growth temperature is 75
The temperature was 0° C., the growth rate was 3 μm/hour, the total gas flow rate was 5 t/min, and the supply molar ratio of group V elements to group II elements was V/III ratio of 20.

Furthermore, as shown in FIG. 2, a photoresist film 3 is coated on the multilayer current blocking layer 10, a part of the central part of the ridge is removed in a stripe shape with a width of 5 μm, and then chemical etching is performed using the photoresist film 3 as a mask. . The etching is continued until a part of the multilayer current blocking layer 10 is completely removed in the depth direction of the groove as shown in FIG.
Continue until exposed. Here the depth of the groove is 1.2μm
And so. Thereafter, the photoresist film 3 is removed and the substrate surface is cleaned, after which a double heterostructure is grown by a liquid phase epitaxial method. Growth temperature 850℃, supersaturation degree 7
Liquid phase epitaxial growth is performed under the growth conditions of 0.5° C. and a cooling rate of 0.5° C./min, and the layers described below are sequentially grown. That is, as shown in FIG. 1, on a p-type GaAs substrate 1 on which a multilayer current blocking layer 10 is formed, a p-type layer a 1+xA
tzA s cladding layer 4 with a thickness of 0.3 μm on the flat part, G
a 1-A bamboo A s active layer 5 (0≦y<x) is 0.08
μm, n-type Ga 1-xAtzAs cladding layer 6 is 2 μm
m, n type layer AAs cap layer 7 was grown to a thickness of 1.5 μm. The p-side control electrode 9 is made of AuZn on the p-type GaAs substrate 1, and the AuGeN is made on the n-type GaAs cap layer 7.
An n-side ohmic electrode 8 is formed on the i.

When the semiconductor laser manufactured as described above is mounted and a current is applied, the current is narrowed by the stripe width of W shown in FIG. Expressing an example of typical laser characteristics within a wafer in terms of a threshold current value, a low threshold current value of 35 mA was obtained at W=2 μm, and the oscillation was stable fundamental transverse mode oscillation. Compared to a conventional BTRS laser with a single-layer current blocking layer, the dispersion of the threshold current value for 30 elements in the BTRS laser manufactured using the method of the present invention is approximately 2/3 that of the conventional one, and the number of minority carriers is reduced. This shows that the effective diffusion length is shortened and the current blocking effect is working effectively.

In this embodiment, GaAs-based and GaAtAs-based semiconductor lasers are described, but the present invention can be similarly applied to semiconductor laser devices made of compound semiconductors including InP-based and other multi-component mixed crystal systems. Furthermore, among the multilayer current blocking layers, except for one layer, which has a conductivity type opposite to that of the substrate,
Any of a non-doped layer, a p-type layer, and an n-type layer may be used, and either GaAs or AtGaAs may be used.

In addition to MOCVD, MBE (molecular beam epitaxial growth) is also used as an epitaxial growth method.
Similar results can be obtained using the taxi method.

(Effects of the Invention) As explained above, according to the present invention, it is possible to easily form an internal stripe structure with good reproducibility, and as a result, it is possible to form a high-performance structure that oscillates in the fundamental transverse mode with a low threshold current value. A semiconductor laser device can be manufactured, and its practical effects are remarkable.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a diagram showing the manufacturing process of the same device, and FIG.
FIG. 4, which is a cross-sectional view of an example of a multilayer current blocking layer, is a cross-sectional view of a conventional semiconductor laser device. 1...p-type QaAs substrate, 2...n-type GaAs layer,
3... Photoresist film, 4... p-type GaAtAs
cladding layer, 5- GaAtAs active layer, 6- n-type layer aAtAs clad layer, 7- n-type GaAs cap layer, 8... p-side ohmic electrode, 9... n-side ohmic electrode, 10... Multilayer current blocking layer, 11...G
aAtAs barrier layer, W...internal stripe width. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 3--Photoresist film Figure 3 Figure 4 Team lane

Claims (3)

[Claims] (1) A first multilayer thin film consisting of three or more layers, including at least one layer having a conductivity type opposite to that of the substrate and having a smaller forbidden band width than other layers, is formed on a conductive substrate having a ridge. a step of forming by an epitaxial method, a step of forming a groove with a depth reaching the substrate from the surface of the first multilayer thin film directly above the central portion of the ridge, and a first multilayer thin film including the groove. A method for manufacturing a semiconductor laser device, comprising the step of forming a second multilayer thin film having a double heterostructure including an active layer by liquid phase epitaxial growth. (2) The method for manufacturing a semiconductor laser device according to claim (1), wherein MOCVD is used as the epitaxial method for forming the first multilayer thin film. (3) A method for manufacturing a semiconductor laser device according to claim (1), characterized in that an MBE method is used as the epitaxial method for forming the first multilayer thin film.