JPH0574237B2 - - Google Patents

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.

Configuration of conventional example and its problems In recent years, demand for high-output semiconductor laser devices that emit fundamental transverse mode oscillation has been increasing in a wide range of fields, such as for writing optical disk files and laser printers. already developed
TRS (Twin-Ridge-Substrate) type semiconductor laser devices meet this demand.

Figure 1 shows a conventional TRS type semiconductor laser device using an n-type substrate.
Each layer including the active layer 3 (n-type Ga ₁ - _y Al _y As clad layer 2, non-doped
After successively growing a Ga ₁ - _x Al _x As active layer 3, a P-type Ga ₁ - _y Al _y As cladding layer 4, and an n-type GaAs electrode forming layer 5, and diffusing zinc from the crystal surface for current injection. , electrodes 6 and 7 are formed on both the upper and lower surfaces.

Due to the anisotropy of crystal growth, this structure suppresses growth on the ridge compared to the sides of the ridge.
An extremely thin active layer can be formed on the ridge with good reproducibility. By making the active layer thinner, the light confinement coefficient within the active layer becomes smaller.
A large amount of light seeps into the cladding layer, and the light that seeps into the first cladding layer 2 is absorbed by the substrate on the ridges other than the grooves, so it is confined in the grooves between the ridges, where a stable fundamental transverse mode is generated. Oscillation is obtained.

However, the conventional structure shown in FIG. 1 has the following problems. (1) The current injected from the zinc diffusion region 8 flows not only to the groove where oscillation occurs but also to the ridges other than the groove, so these currents not only result in losses but also reduce the effective current flowing to the groove. Inhibits injection. (2) Heat diffusion of zinc to a desired depth in stripes with good reproducibility is problematic in terms of controllability, so the diffusion front may not reach the second cladding layer 4 or reach the active layer 3. In some cases, this 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 in which the above-mentioned problems are solved, and a method for manufacturing the same.

Structure of the Invention To achieve this object, a semiconductor laser device of the present invention includes a substrate having a groove, and a layer having a conductivity type opposite to that of the substrate except for the groove portion, and a layer having a conductivity type opposite to that of the substrate. The mold layer has steps on both sides of the groove to form two parallel ridges, and each layer including the active layer is formed on a substrate having the ridges. Further, the method for manufacturing a semiconductor laser device of the present invention includes a step of growing at least one layer on a substrate so that the conductivity type is alternately changed, and a step of growing parallel striped layers on the substrate on which the growth has been performed. The bottom surface of the groove between the ridges is below the step surface on the outside of the ridge and reaches the substrate, and the step surface is formed so that it does not reach the substrate; It is formed from the steps of forming each layer including the active layer.

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

First, an n-type GaAs blocking layer 10 is grown to a thickness of 2.0 μm on the surface of a p-type GaAs substrate 9 by liquid phase epitaxial method (FIG. 2a). This first
A width of 20 μm was
Two ridges are formed by etching with a groove of width 4 μm in between. The depth of the groove between the ridges is approximately
The thickness is 2.2 μm, and the bottom reaches the p-type substrate 9. On the other hand, the height of the outside of the ridge is about 1.1 μm, and the blocking layer 10 remains on the surface (FIG. 2b).

A first layer of p-type Ga ₁ - _y is then deposited on the surface of the substrate 9 on which the ridges have been formed again by epitaxial method.
The thickness of the Al _y As cladding layer 11 above the ridge is approximately
Similarly, the thickness of the second layer of non-doped Ga ₁ - _x Al _x As active layer 12 is approximately 0.05 μm, and the third layer of n-type Ga ₁ - _y Al _y.
The As cladding layer 13 is similarly grown to a thickness of approximately 1.5 μm, and the fourth layer n-type GaAs electrode forming layer 14 is similarly grown to a thickness of approximately 2.0 μm.
Figure c).

In addition, in the above example, x=0.08, y=
It is 0.43. A metal for the n-side electrode is deposited on the fourth electrode forming layer 14, and an alloying process is performed to form the n-side electrode.
A semiconductor wafer of the present invention is obtained by forming a side ohmic electrode 15, depositing a metal for a p-type electrode on the substrate side, and performing an alloying process to form a p-side ohmic electrode 16.

Since the semiconductor laser device of this embodiment has the above structure, the pn junction is reverse biased by the action of the blocking layer formed in the first epitaxial growth, thereby blocking 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 experiments, the oscillation threshold is approximately
At 30mA, the external differential quantum efficiency was approximately 70%, and it was confirmed that a lower threshold and higher efficiency can be obtained compared to conventional TRS semiconductor lasers.

In addition, in the structure of this example, the passage of current is limited to the groove between the ridges, so there is no need for zinc diffusion for current injection, which is required in conventional TRS semiconductor lasers, which reduces the variation in the depth of zinc diffusion. This eliminates the decrease in oscillation rate caused by this, and it is possible to greatly simplify the steps after epitaxial growth.

Although this embodiment has been described using a p-type substrate, it goes without saying that the same implementation can be achieved 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 in a simple process. The practical effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional semiconductor laser device, and FIGS. 2 a to 2 c are sectional views at each step of a method for manufacturing a semiconductor laser device according to an embodiment of the present invention. 1... n-type GaAs substrate, 2... n-type Ga ₁ - _y Al _y
As crust layer, 3...non-doped Ga ₁ − _x Al _x As
Active layer, 4... p-type Ga ₁ - _y Al _y As cladding layer, 5
... n-type GaAs electrode formation layer, 6 ... p-type ohmic electrode, 7 ... n-type ohmic electrode, 8 ... zinc diffusion region, 9 ... p-type GaAs substrate, 10 ... n-type
GaAs blocking layer, 11... p-type Ga ₁ - _y Al _y
As clad layer, 12...non-doped Ga ₁ − _x Al _x
As active layer, 13... n-type Ga ₁ - _y Al _y As cladding layer, 14... n-type GaAs electrode forming layer, 15... n
type ohmic electrode, 16...p side ohmic electrode.

Claims (1)

[Scope of Claims] 1. A substrate of a predetermined conductivity type having striped grooves with flat bottoms on the surface, two ridges parallel to each other and with flat tops on both sides of the grooves on the substrate. a layer of opposite conductivity type, which fills the groove between the two ridges and forms a flat surface spanning each top surface of the two ridges, and a cladding layer having a step on the outside of both ridges; A semiconductor laser device with a thick active layer. 2. A process of growing at least one layer on a substrate so as to change the conductivity type, and forming striped ridges parallel to each other and having a flat top surface on the substrate on which the growth has been performed, and forming a layer between the ridges. a step of forming the groove so that the bottom surface is flat and reaches the substrate below the step surface on the outside of the ridge, and the step surface does not reach the substrate; A method of manufacturing a semiconductor laser device, comprising the step of forming each layer including a cladding layer so that the active layer is flat across the groove and straddles both ridges.