JPS6297384A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To improve the maximum optical output, by forming each layer including an active layer on a substrate, on which two parallel ridges, whose width becomes narrow in the vicinity of an end surface, are formed. CONSTITUTION:Widths WR of ridges 2a and 2b are different in the vicinity of the center (A-A') and in the vicinity of an end surface (B-B') in a laser chip. In this BTRS laser device, the smaller the width WR of the ridges 2a and 2b, the thinner the thickness of a grown film on the ridges. In liquid phase epitaxial growing, the slower the growing speed of an active layer 4, the larger the composition ratio of Al in a crystal and the larger the forbidden band width tends to become. Therefore, the film thickness dB of the active layer in the vicinity of the end surface of the laser chip becomes thinner than the film width dA in the vicinity of the center. As a result, the forbidden band width becomes large only in the vicinity of the end surface. Therefore, laser light emitted in the laser chip is not absorbed in the vicinity of the end surface, and end surface breakdown, which determines the maximum optical output of the laser device, is hard to occur.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a semiconductor laser device.

2. Description of the Related Art In recent years, there has been an increasing demand for high-power semiconductor laser devices that emit fundamental transverse mode oscillation for use in a wide range of fields such as writing optical disk files and laser printers. In order to meet this demand, the present inventors have developed BTRS (Burried Twin-Rigging System).
We have proposed a semiconductor laser device with an e5ul)strate) structure. Its cross section is shown in FIG. p-type G a A
A mesa 1a is formed on an s-substrate 1, and an n-type G
a As current confinement layer 2 is grown.

Two parallel ridges 2a and 2b are formed in the current narrowing layer 2. On top of that is a p-type Ga1-xAlxAs cladding layer 3. Non-doped Ga1-AlyAs active layer 4゜n
Type Ga1. -, AlxAs cladding layer5. n-type Ga
A B contact layer 6 is grown by liquid phase epitaxial growth, after which electrodes 7.8 are formed. The current injected from the substrate 1 flows through the two ridges 2a on the mesa 1a,
2t) and is efficiently injected only into the light emitting region of the active layer 4. On the other hand, due to the anisotropy of crystal growth, the growth on the ridges 2a, 2b is suppressed compared to the side surfaces of the ridges 2a, 2b, so an extremely thin active layer can be formed on the ridges 2a, 2b. As a result of this thinning of the active layer, the light confinement coefficient within the active layer becomes smaller, so the light seeps out into the cladding layer, increasing the light emitting spot size and reducing the optical power density at the light emitting end face. be able to. In this way, efficiency of current injection,
By making the active layer thinner, it is possible to increase the output power of a semiconductor laser. On the other hand, the light seeping into the first cladding layer 3 is absorbed by the substrate 1 on the ridges 2a, 21) other than the grooves, so it is confined in the grooves between the ridges 2a, 2b, where the basic horizontal Mode oscillation is obtained.

Problems to be Solved by the Invention However, with the above configuration, as the output increases, the absorption of light at the end face increases, eventually causing destruction. This level of destruction was the most important factor in determining the maximum optical output of a semiconductor laser device.

In view of the above drawbacks, the present invention aims to provide a semiconductor laser device that takes advantage of the characteristics of the BTR8 structure, has less light absorption near the end facets, and can achieve higher output than conventional devices.

Means for Solving the Problems In order to solve the above problems, in the semiconductor laser device of the present invention, a layer having a conductivity type opposite to that of the substrate is formed on a substrate having a projection, and a layer having a conductivity type opposite to that of the substrate is formed. A groove is formed that reaches the protrusion from the surface of the conductive layer, and two parallel ridges are formed on both sides of the groove so that the width becomes narrower near the end surface, and an active layer is formed on the substrate having the ridge. Each layer including layers is formed and configured.

Effect: This configuration reduces light absorption near the end face.
Higher output can be achieved.

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

<011 on the (ioo) plane of the p-type GaAs substrate 1
> forms a mesa in the direction. Mesa width is Bpm, height is 1
．． The diameter was set at 7 μm (Fig. 2a). An n-type GaAs current confinement layer 2 is formed on this substrate by liquid phase epitaxial growth.
was grown until the film thickness on the mesa was 1.0 μm (Figure 2b). Thereafter, two parallel ridges 2a, 21) were formed by etching. The width of the ridges 2a and 2b was 5 pm within 10 .mu.m from the end face, and 20 .mu.m elsewhere.

The height of the ridges 2a and 2b was set to 1.5) trn, and the width of the groove of the ridges 2a and 2b was set to 4 μm (FIG. 2C).

A third n-type Ga AI As cladding layer 3 was formed on this substrate by a liquid phase epitaxial growth method.
57 0.43 0.2)tm in the flat part on the ridges 2a and 2b, second layer non-doped G a Al! A s active layer 4 at the same 0.92 0.08 location, approximately 0.05/1 m, third layer n-type Ga AI
AsO,570,43 Cladding layer 5 is 1.577m at the same location, 4th layer n-type G
The a As contact layer 6 was continuously grown at the same location to a thickness of 4.0 μm (FIG. 2d).

Thereafter, a metal for an n-side electrode was deposited on the growth surface, and an alloying process was performed to form an n-side ohmic electrode 7.

A p-side electrode metal was deposited on the substrate side and alloyed to form a p-side ohmic electrode 8 (FIG. 2d). This wafer is interbonded and mounted on a Si chip to complete the process.

The reason why the semiconductor laser device of this embodiment configured as described above allows a BTRS laser device with a window structure in which laser light is not absorbed near the end face to be obtained will be explained below.

Cross-sectional views along lines A-A' and B-B/ in FIG. 2d are shown in FIGS. 1a and b, respectively. Near the center of the laser chip (A-
A/) and near the end face (B-B').

This is a BTRS laser device in which the widths WR of the beams 2a and 2b are different. By the way, in the BTRS laser device,
As shown in FIG. 3, the ridge 2a.

A feature is that the smaller the width WR of 2b, the thinner the grown film on the ridge becomes. Furthermore, in liquid phase epitaxial growth, as shown in FIG. 4, the slower the growth rate of the active layer, the greater the composition ratio of A4 in the crystal, which tends to increase the forbidden band width.

From the results in FIGS. 3 and 4, as shown in FIGS. 1a and 1b, the active layer film thickness dB near the end face of the laser tip is thinner than the film thickness dA near the center of the laser chip, and as a result, The forbidden band width increases only near the end face. The situation is shown in FIG. As is clear from the figure, the laser light generated inside the laser chip is not absorbed near the end face because the forbidden band width is large (window effect). Therefore,
Since end face destruction occurs which determines the maximum optical output of the laser device, a very large optical output can be obtained. fact,
The window type BTRS laser device manufactured based on this example was able to achieve a high output of a maximum optical output of 200 mW.

In addition, as an example, an example in which the ridge is narrow in parallel near the end face has been shown, but as another example, as shown in the top view of the ridge in Fig. 6 a, l), the ridge is Even if the width is gradually narrowed, exactly the same effect is produced.

Effects of the Invention As described above, in the semiconductor laser device of the present invention, each layer including the active layer is formed on a substrate in which two parallel ridges whose widths are narrow near the end facets are formed, so that laser irradiation at the end facets is achieved. It can reduce the absorption of device light and increase the maximum light output, and has great practical value.

[Brief explanation of drawings]

Figures 1a and 1) are cross-sectional views near the center and near the end face of a semiconductor laser device according to an embodiment of the present invention, respectively, and Figures 2a+b+c and d are cross-sectional views of a semiconductor laser device according to an embodiment of the present invention. 3 is a characteristic diagram showing the relationship between the ridge width and the film thickness on the ridge in a BTRS laser device, and FIG. 4 is a relationship between the growth rate of the active layer and its forbidden band width in liquid phase epitaxial growth. FIG. 6 is a diagram showing the distribution of the forbidden band width of the active layer of the window type BTRS laser device of the first embodiment, and FIG. The top view and FIG. 7 are cross-sectional views of a conventional BTRS type laser device. 1...p-type GaAs substrate, 2...n-type G
a As current confinement layer, 3...p-type Ga1-
Air AlxAs cladding layer, 4...Non-doped Ga1-AlyAs active layer, 6...
n-type Ga1-AirA lxA s cladding layer, 6...
... n-type Ga As contact layer, 7... group n-type ohmic electrode, 8... p-type ohmic electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person f-
P Yuki LGaA & Kimusuee, 5--11 Yuki =
Figure 2 Figure 3 Figure 5 11 Wind tilt - K
Quinto Area Figure 6 Figure 7

Claims (1)

[Claims] A layer of a conductivity type opposite to that of the substrate is formed on a substrate having a protrusion, and a groove is formed reaching the protrusion from the surface of the layer of the opposite conductivity type, so that a groove is formed on both sides of the groove. A semiconductor laser device characterized in that two parallel ridges are formed so that the width becomes narrower near the end face, and each layer including an active layer is formed on a substrate having the two ridges.