JPS5969984A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture the titled laser device with a crescent-shaped active layer formed on a grooved substrate by a method wherein various layers including an active layer are formed on a substrate with a devetail groove the depth of which fluctuates discontinuously while the lower surface of the active layer above the groove is formed into a convex crescent-shape. CONSTITUTION:A first N type clad layer 2, a second active layer 3, a third P type clad layer 4 and a fourth current limiting layer 5 are continuously grown on an N type substrate 1. A dovetail groove is formed on the substrate 1 either by an etching before the growth or by utlizing both the etching before the growth and the melt-back in case of the growth. The active layer 3 thus formed on the groove is formed into crescent-shape by means of adjusting the growing time of the first clad layer 2. After growing the fourth current limiting layer 5, a P type impurity is selectively diffused into stripe type to make the diffused front reach the third clad layer 4. After removing a diffusion preventing film 17 grown on the crystal surface for the selective diffusion, a P side ohmic electrode 6 may be formed while N side ohmic electrode 7 may be formed likewise on the substrate side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser device and a method for manufacturing the same.

Conventional configurations and their problems In recent years, there has been a demand for semiconductor lasers that oscillate in fundamental transverse mode at a low threshold as light sources for loading and reading information into DADs, optical disk files, etc., or as light sources for optical communications. has been done. An effective way to achieve this is to create a refractive index distribution in the cross section of the semiconductor laser in a direction parallel to the active layer. has been announced.

FIGS. 1(a) and 1(b) each show a cross-sectional view of a conventional semiconductor laser. Figure 1(a) (is CS P (Ch
anneled -3ubstrate -Plana
r) What is called a v-za, 1 is an n-type GaAs substrate, 2 is an n-type Ga1xAlxAs 11 layer, 3 is a non-doped Ga, ', A, dyAs active layer,
4 is a P-type Ga1-xA1xAS cladding layer, 5 is an n-type G
aAs current limiting layer, 6 a metal film for the P-side ohmic electrode,
7 is a metal film for an ohmic electrode on the n-side, and 8 is a zinc diffusion region. By providing a groove on the substrate 1, the laser
This is intended to trap light leaking from the active layer 3 into the cladding layer 2.degree. by creating a dynamic refractive index difference between the inside and outside of the groove.

In addition, FIG. 1(b) shows B C (Buried Cres
cent) is called a laser, and 7 is n 1ill
Metal film for ohmic electrode, 8 is a zinc diffusion region, 9 is an n-type InP substrate 5, 10 is an n-type IHGaAsP layer, 11 is a P
12 is an n-type InP cladding layer, 13 is a non-doped InGaAsP active layer, 13' is a crescent-shaped non-doped InGaAsP active layer, 14 is a p-type InP cladding layer, 15 is an n-type 11GaAsP current limiting layer, 16 is cadmium This is a diffusion area. This laser attempts to confine light in the lateral direction by embedding a crescent-shaped active layer 13' due to the shape of the active layer.

However, in the above-mentioned asp laser, since the effective refractive index difference in the lateral direction is small, there is a possibility that light and carriers may not be sufficiently confined. Furthermore, since the Be laser requires steps such as growing the active layer twice, it is labor intensive to manufacture and is disadvantageous in terms of cost.

The present invention eliminates the above-mentioned conventional drawbacks and ? ? The object of the present invention is to provide a semiconductor laser with a new structure in which a crescent-shaped active layer is formed on a substrate, and a method for manufacturing the same.

In other words, in the semiconductor laser device of the present invention, each layer including the active layer is formed on a substrate in which a dovetail groove whose depth changes discontinuously is formed, and the upper part of the groove is formed on the substrate. The active layer is characterized in that it has a downwardly convex crescent shape.

Furthermore, the method for manufacturing a semiconductor laser device of the present invention includes a step of forming a groove on the surface of a semiconductor substrate, and epitaxially growing each layer including an active layer on the surface of the semiconductor substrate, so that the groove has a discontinuous depth. The active layer deforms into a dovetail shape that changes into a dovetail shape, and the active layer forms a downwardly convex crescent shape above the dovetail groove.

DESCRIPTION OF THE EMBODIMENTS On an n-type substrate 1, as shown in FIG.
, the fourth layer current limiting layer 5 is continuously grown. The tabtail-shaped grooves shown in the figure are formed on the substrate by etching before growth.
Alternatively, it is formed by a combination of etching before growth and tartback during growth. The active layer formed on such a groove has a crescent shape as shown in the figure by adjusting the growth time of the first cladding layer 2. Fourth
After growing up to the layer current limiting layer 5, the p-type impurity is selectively diffused in a stripe pattern so that the diffusion front reaches the third cladding layer 4 (Fig. 2(b)). After removing the diffusion prevention film 17 attached to the surface, the p-side ohmic electrode 6 is formed.

In addition, an n-side ohmic electrode 7 is formed on the substrate side, as shown in FIG.
Produce as in C1.

In a semiconductor laser with this structure, a crescent-shaped active layer, which is effective for confining laser light and carriers, can be formed in only one growth process, which requires less work and number than the conventional two-step growth method. It is very advantageous in terms of cost since it requires much less and a higher yield can be expected.

By making the shape of the groove into a dovetail shape, 31"
One of the features of this structure is that it is possible to form the moon's active layer with good reproducibility.

Examples of the laser of the present invention constructed by the liquid phase epitaxial method using GaAs-4aA and gAs will be described in more detail below.

(01'+") on the (1oo) plane of the n-type GaAs substrate 1
The third layer has a depth h or 1.5 μm in the direction, and a width W at the bottom of 5 μm.
An NLT having the shape shown in the figure is formed by etching.

A fourth layer of n-type GaAs (J
o, s5A S cladding layer 2 is placed on the substrate flattened portion outside the groove portion approximately 0.2 μm % 2nd layer non-doped 0.95 A
(The thickness of the 10,05As active layer 3 at the center of the groove is approximately 0.1 μm.
, the third layer p-type Ga065A#0.35 As cladding layer 4 has a thickness of about 1.5 μm, and the fourth layer n-type GaAs 5 has a thickness of about 0.35 μm.
Continuous growth is performed to a thickness of 5 μm (FIG. 2(a)). When growth is continued from a constant temperature of 790'C with supercooling of 5'C, the shape of the groove changes to that shown in Figure 2 (Fig. 2) due to meltback.
It changes into a dovetail shape as shown in a) and (b),
The width of the upper part of the groove is approximately 7 μm. The active layer above the groove has a crescent shape as shown in the figure. Next, 813N4 is applied to the growth surface.
A film 17 is applied, a striped window is formed on the top of the groove of the substrate, and selective diffusion is performed there, so that the diffusion front is in the third layer p.
It is made to reach the Gao6sAno55As cladding layer 4 (FIG. 2(b)). After that, Si3N on the surface
4 film 17 is removed, p-side electrode metal is deposited, and alloying is performed to form p-side ohmic electrode 6. A metal for the n-side electrode is deposited on the substrate side and alloyed to form the n-side ohmic electrode 7 (FIG. 2(C)).

The semiconductor wafer produced in this way is cleaved and S
Complete the semiconductor laser by placing it on one block.0 With the laser structure using the manufacturing method described above,
Fundamental transverse mode oscillation with a threshold of about 50 mA and an optical output of 40 mW could be obtained.

As described in detail, the method for fabricating a semiconductor laser device of the present invention has the advantage that the active layer can be easily formed by only one growth, so that the manufacturing process requires only a single peak i and j.

[Brief explanation of drawings]

Figure 1 (a) shows the conventional Q S P (G: hannel
ed-8ubstrate-Planar) Cross-sectional view of the laser, Figure 1 (bl is the conventional B C (Buri
ed Crescent) A cross-sectional view of the laser, FIG. It is a sectional view of a substrate used for manufacturing. 1--n' type G&AS substrate, 2-... n-type Ga
1xA 1xAs cladding layer, 3...Non-doped Ga
t yA y ASt occupancy layer, 4...p-type Ga I
X A lx A s cladding layer, 5...n
type GaAs current limiting layer, 6...p'11 metal film for ohmic electrode, 7...metal film for n-side ohmic electrode, 8...zinc diffusion region, 9.・・・・・・
n-type InP substrate, 10...n-type InCraAsP layer, 11-==p-type InP layer, 12... npIn
P cladding layer, 13...non-doped InGaA
s P active layer, 14... p-type InP cladding layer,
1 B-・-=-n-type InGaAsP current limiting layer, 16
．． ,. ...Cadmium diffusion region, 17...Insulating film. Name of agent: Patent attorney Toshio Nakao and 1 other person36
9- Figure 1 Figure 3

Claims (2)

[Claims] (1) Each layer including an active layer is formed on a substrate in which a dovetail groove whose depth changes discontinuously is formed, and the active layer above the groove has a downwardly convex shape. A semiconductor laser device characterized by having a crescent shape. (2) forming a groove on the surface of the semiconductor substrate, epitaxially growing each layer including the active layer on the surface of the semiconductor substrate, deforming the groove into a dovetail shape whose depth changes discontinuously, and forming the groove on the surface of the semiconductor substrate; The layer is convex downward at the top of the gubtail-shaped groove.