JPS60158684A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the efficiency of oscillation by forming a ridge having a conduction type reverse to a substrate to the substrate with a projection, to which a striped groove is formed, and shaping each layer containing an active layer on the ridge. CONSTITUTION:Two parallel erected ridges are formed to the surface of a wafer, in which a blocking layer 10 is grown on a P type GaAs substrate 9 to which a projection is shaped, while holding a groove. The groove is positioned just above the projection, and the bottom of the groove reaches to the P type substrate 9 while the blocking layers 10 are left on the outside of the ridges. A P type clad layer 11, a non-doped active layer 12, an N type clad layer 13 and an N type electrode forming layer 14 are grown continuously on the surface of the substrate 1. An N side ohmic electrode 15 is formed on the electrode forming layer 14 and a P type ohmic electrode 16 on the substrate side. Accordingly, currents can be injected concentrically to the active layer, and a laser device having a low oscillation threshold can be manufactured simply.

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 configuration and its problems In recent years, there has been an increasing demand for high-power semiconductor laser devices that emit fundamental transverse mode oscillation in a wide range of fields, such as for writing optical disk files and laser printers. The developed TR8 (Twin-Ridge
-8ubstrate) type semiconductor laser devices meet this demand.

FIG. 1 shows a conventional TR8 type semiconductor laser device using an n-type substrate, in which two ridges standing parallel to each other are formed on a substrate 1, and each layer 2, 3, 4 including an active layer 3 is formed on the substrate 1. After continuous growth of .6 and diffusion of zinc from the crystal surface for current injection, electrodes 6 and 7 are formed on both upper and lower surfaces. In this structure, the growth on the wide ridge is suppressed due to the anisotropy of crystal growth compared to the side surfaces of the ridge, so that an extremely thin active layer can be formed on the ridge with good reproducibility. This thinning of the active layer reduces the confinement coefficient of light within the active layer, so light seeps into the cladding layer to a large extent, and the light that seeps into the 1st and 11th layer 2 is trapped on the ridges other than the grooves. Since it is absorbed by the substrate, it is confined in the groove between the ridges, where stable fundamental transverse mode oscillation can be obtained.

However, the conventional structure shown in FIG. 1 has the following problems. (The current injected from the zinc diffusion region 8 flows not only into the groove where oscillation occurs, but also into the ridge other than the groove, so the current in the other parts is not only a loss, but also an effective current flowing into the groove.) (2) The diffusion front does not reach the second cladding layer 4 because it is difficult to thermally diffuse zinc in a stripe pattern to any depth with good reproducibility in terms of controllability. In some cases, it may even reach the active layer 3, which is a major cause of lowering the oscillation rate.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a semiconductor laser device having a novel structure that solves the above-mentioned problems, and a method for manufacturing the same.

Structure of the Invention In order to achieve this object, a semiconductor laser device of the present invention is provided, in which a layer having a conductivity type opposite to that of the substrate is formed on a substrate provided with striped protrusions having grooves, except for the grooves. In addition, the layers of opposite conductivity types have steps on both sides of the protrusion to form two ridges, and each layer including an active layer is formed on the substrate having the ridge.

Further, the method for manufacturing a semiconductor laser device of the present invention includes a step of forming striped protrusions on a substrate, alternating conductivity types on the substrate on which the protrusions are formed, and filling the protrusions completely. the bottom of the groove between the ridges reaches the upper end of the protrusion, and the bottom surface of the step outside the ridge is The method consists of a step of forming the ridge so that it does not reach the substrate, and a step of forming each layer including the active layer on the substrate having the ridge.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 2a to 2d show cross-sectional views of each step of a method for manufacturing a semiconductor laser according to an embodiment of the present invention.

A blocking layer 10 is applied to the surface of a p-type GaAs substrate 9 (Fig. 2a) on which protrusions of 2.2 μm in height and 10 μm in width are formed by etching.The thickness above the protrusions is O.S μm and the surface becomes flat. (Figure 2b).

On the surface of the wafer after this first growth, a height of 1
．． Two parallel upright ridges of 6 .mu.m width and 20 .mu.m width are formed by etching with grooves of 4 .mu.m width.

The groove between the ridges is located directly above the protrusion and its bottom is reached at the p-type substrate 9'=1. On the other hand, the blocking layer 10 remains on the flat part outside the ridge even after etching (Fig. 2C).
).

A first layer of p-type Ga1. AjA%A
The thickness of the s-cladding layer 11 on the ridge is approximately 0.2 μm.
, the second layer of non-dawg Ga1. , cklxAs active layer 1
2 to about 0.06 μm, and the third layer of n-type Ga4. Al
Similarly, the yAs cladding layer 13 is continuously grown to a thickness of about 1.5 μm, and the fourth nm GaAs electrode forming layer 14 is similarly grown to a thickness of about 20 μm (FIG. 2d).

In the above example, :=o, os, y−〇A3
It is. A metal for the n-side electrode is deposited on the fourth electrode forming layer 6, and an alloying process is performed to form the n-side ohmic electrode 1.
A p-type ohmic electrode 16 is formed by depositing a p-type electrode metal on the substrate side and performing an alloying process.

Since the semiconductor laser device of this embodiment has the above configuration, there are five features as described below.

(1) The blocking layer formed in the first epitaxial growth creates a reverse bias state of the pn junction and blocks current flow. Therefore, the current injected from the substrate side is intensively injected into the active layer above the groove where oscillation occurs. As a result, the oscillation threshold can be lowered and the external differential quantum efficiency can be improved. As a result of the experiment, it was confirmed that the oscillation threshold was about 30 mA and the external differential quantum efficiency was about 70%, which resulted in a lower threshold and higher efficiency than the conventional TR8 type semiconductor laser.

(2) The blocking layer formed in the first epitaxial growth completely fills the protrusions previously formed on the substrate and grows so that the surface is flat, so the depth of the groove between the ridges and the height of the step on the outside of the groove are Because it can be made the same.

This can be done in one etching.

(3) Since the semiconductor laser of this embodiment allows current to pass only through the groove between the ridges, there is no need for zinc diffusion for current injection, which is required in the conventional 1'R3 semiconductor laser. Since the oscillation rate is reduced by iy<m due to the variation in the depth of the epitaxial layer, the steps after epitaxial growth can be greatly simplified.

Note that although the embodiment has been described using a p-type substrate, it goes without saying that the same implementation can be performed using an n-type substrate, and the same effect will be obtained.

Effects of the Invention As described above, according to the present invention, by intensively injecting current into the active layer, a semiconductor laser device with a low oscillation threshold can be manufactured through a simple process, and its practical use can be improved. The effect is like a dog.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional semiconductor laser device, and FIG. 2 is a cross-sectional view of each step of the method for manufacturing a semiconductor laser device of the present invention. 1----= n-type GaAs substrate, 2...n-type G
a1. AlyAs cladding layer, 3...non-doped Ga1. A#xAs active layer, 4...p-type Ga
11A 1. y A S advanced layer, 6...
n-type GaAs electrode forming layer, 6... p-type ohmic electrode, 7... n-type ohmic electrode, 8...
...Zinc diffusion region, 9...p-type GaAs substrate,
1o...N-type GaAs7'o soaking layer, 11
-n-type Ga4. AiyAs. Cladding layer, 12...Non-doped Ga, -x A
ex As active layer, 13...n-type Ga1-A
ly As cladding layer, 14...n-type Ga
A s electrode forming layer, 15...n-side ohmic electrode, 16...p-side ohmic electrode. Name of agent: Patent attorney Toshio Nakao (1st person)
figure

Claims (2)

[Claims] (1) A layer of a conductivity type opposite to that of the substrate is formed on a surface other than the groove portion of a substrate having a protrusion with striped grooves formed on the surface, and the layer of the opposite conductivity type has a step on both sides of the protrusion. 1. A semiconductor laser device characterized in that two parallel ridges are formed by forming two parallel ridges, and each layer including an active layer is formed on a substrate having the ridges. (2) forming striped protrusions on the substrate;
a step of growing at least one layer on the substrate in which the protrusions are formed, alternating the conductivity type and filling the protrusions; forming two ridges parallel to each other in the form of stripes in a direction such that the bottom of the groove between the ridges reaches the upper end of the protrusion, and the lower surface of the step outside the ridge does not reach the substrate; 1. A method for manufacturing a semiconductor laser device, comprising: forming each layer including an active layer on a substrate having a ridge.