JPH0632327B2 - Semiconductor laser device and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser device, which has rapidly expanded in use and is in high demand as a light source for various electronic devices and optical devices.

(Structure of Conventional Example and Problems Thereof) One of the important performances required for a semiconductor laser as a coherent light source for electronic devices and optical devices is oscillation at a single spot, that is, single transverse mode oscillation. In order to realize this, it is necessary to suppress the spread and confine the light so that the current flowing in the laser element is concentrated near the active region where the laser light propagates. Such a semiconductor laser is usually called a stripe type semiconductor laser.

A relatively simple striping method uses only current narrowing. Although these lasers realize single transverse mode oscillation, their threshold value is high. There is a buried stripe type semiconductor laser (generally called a BH laser) as a stripe structure which has the lowest threshold. However, in order to manufacture this laser, the crystal growth step, which is usually performed once with other lasers, is required twice, and it is technically somewhat difficult to manufacture.

(Object of the Invention) In view of the above drawbacks, the present invention provides a semiconductor laser device capable of producing a buried stripe structure required for single transverse mode oscillation and low threshold voltage operation by one-time crystal growth, and a method of manufacturing the same. Is provided.

(Structure of the Invention) In order to achieve this object, a semiconductor laser device of the present invention comprises a first multi-layered thin film having a double heterostructure including an active layer on a stripe-shaped inverted mesa-shaped convex portion of a substrate of one conductivity type. Is formed, and even on both side surfaces of the inverted mesa-shaped convex portion, up to the thin film layer directly above the active layer, the second layer is formed in the same order in the stacking direction.
Is independently formed, a thin film having a conductivity type opposite to that of the substrate is formed directly on the first multilayer thin film, and has the same conductivity type as the substrate on the second multilayer thin film. A thin film is formed.

With the above configuration, a current can be narrowed in the active layer on the stripe-shaped inverted mesa-shaped convex portion, and a semiconductor laser device with single transverse mode oscillation and low threshold operation can be realized. If a metalorganic vapor phase epitaxial growth method or a molecular beam epitaxial growth method is used as the method for manufacturing the semiconductor laser device, the embedded stripe structure can be easily formed by one-time crystal growth.

(Explanation of Examples) A semiconductor laser device and a method for manufacturing the same according to the present invention will be specifically described with reference to an example.

As an example, an n-type GaAs substrate is used as the conductivity type substrate.

FIG. 1 is a cross-sectional view of a semiconductor laser device, and 10 is an n-type in which a stripe-shaped inverted mesa-shaped convex portion 10a is formed in the central portion.
GaAs substrate, 11 is n-type Ga _1-x A formed on the substrate 10.
l _x As clad layer, 12 is an undoped Ga _1-y Al _y As active layer formed on the clad layer 11, and 13 is a p-type Ga _1-x Al _x As clad layer formed on the active layer 12. , 14 are n-type Ga
As cap layer, 15 indicates a p-type GaAs region.

Next, a method of manufacturing the semiconductor laser device having the above structure will be described. As shown in FIG. 3, on the (100) plane of the n-type GaAs substrate 10, as shown in FIG. 2, a photoresist 16 having a width d is used as a mask to form concaves and convexes parallel to the <011> direction by chemical etching. Such a stripe-shaped inverted mesa-shaped convex portion 10a having a width of 5 μm and a height of 1.5 μm is formed. Next, the n-type Ga _1-x Al _x As cladding layer 11 is 1.5 μm thick and the undoped Ga _1-y Al _y As active layer 12 (0 ≦ y <x) is formed by metalorganic vapor phase epitaxial growth method (usually MOCVD method). To 0.08
After forming the p-type Ga _1-x Al _x As cladding layer 13 having a thickness of 1.2 μm, the n-type cap layer 14 is grown to have a thickness of 2 μm. As an example, the crystal growth condition is a growth rate of 2 μm /
At this time, the growth temperature is 770 ° C., the total gas flow rate is 5 / min, and the molar ratio of the group V element to the group III element is 40. As shown in FIG. 4, up to the p-type Ga _1-x Al _x As clad layer 13, epitaxial growth is performed independently on the convex portion and other portions, and the growth material diffuses in a direction parallel to the growth substrate surface. The crystal growth with the effects such as the above is not observed.

After crystal growth, after cleaning the surface, applying photoresist 17 and rotating at 5000 rpm, as shown in FIG. 4, the convex portions become thin and the other portions become thick. By optimizing the exposure conditions, the photoresist film 1 on the convex portion 1
Only 7 is removed, and the convex portions of the n-type GaAs cap layer 14 are removed by etching to form the surfaces 18 and 19 shown in FIG. Further, Zn diffusion is performed with a width w to form stripes. As a result, the semiconductor laser structure shown in FIG.
Put on 0, 21. When current injection is performed, the current is n-type GaAs.
P-type GaAs region 1 formed by projections and diffusion of substrate 10
By 5, the upper and lower sides are narrowed. As a result, a semiconductor laser device having a single transverse mode oscillation with a threshold current value of 30 mA was obtained. As shown in FIG. 5, in the crystal growth on the convex portion of the stripe-shaped forward mesa shape, when the epitaxial growth layer grows to a certain thickness or more, the epitaxial growth layers 25 and 27 do not grow independently, An epitaxial growth layer 26 is formed between them, and the epitaxial growth layers 25, 26 and 27 are crystal-grown as the same epitaxial growth layer.

Therefore, even if an attempt is made to form the semiconductor laser structure of the present invention, the p / n junction does not play a role of current blocking on both side surfaces of the convex portion, so that not only low threshold current value operation cannot be realized but also laser oscillation occurs. There will be no.

Further, the semiconductor laser structure of the present invention is of a buried type, and other buried lasers require crystal growth twice, whereas the buried laser of the present invention can be manufactured by one crystal growth. It is possible. In FIG. 1, an n _- type Ga substrate 10 and an n-type Ga _1-x Al _x As cladding layer 11 are provided between
Similar results were obtained with a structure including an As buffer layer.

In this embodiment, the GaAs-based and GaAlAs-based semiconductor lasers have been described, but the present invention can be similarly applied to a semiconductor laser made of a compound semiconductor containing InP 3 or other multi-element mixed crystal system. Furthermore, regarding the conductive type substrate,
Even if a p-type substrate is used, another crystal growth method with material supply rate control, for example, a molecular beam epitaxial growth method (MBE method) may be used for crystal growth.

(Effect of the Invention) The semiconductor laser device and the method of manufacturing the same according to the present invention realize an embedded laser that oscillates in a single transverse mode at a low threshold current value with a single crystal growth. Is remarkable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a semiconductor laser device according to an embodiment of the present invention, FIGS. 2 to 4 are diagrams showing a manufacturing process thereof, and FIG.
The figure is a diagram showing a crystal growth shape on a convex portion having a normal mesa shape. 10 ... n-type GaAs substrate, 11 ... n-type Ga _1-x Al _x As clad layer, 12 ... Ga _1-y Al _y As active layer, 13 ... p-type Ga _1-x A
l _x As clad layer, 14 …… n-type GaAs cap layer, 15 ……
p-type GaAs region, 16 ... Photoresist film for mesa etching, 17 ... Photoresist film, 18 ... Epitaxial growth surface, 19 ... Etched surface, 20, 21
... ohmic electrode fabrication surface, w ... current narrowing stripe width, d ... mesa mask width, 24 ... GaAs substrate having forward mesa-shaped convex portions, 25, 26, 27 ... epitaxial growth layer.

Claims (3)

[Claims] 1. A first multi-layered thin film having a double heterostructure including an active layer is formed on a stripe-shaped inverted mesa-shaped convex portion of a substrate of one conductivity type, and both side surfaces of the inverted mesa-shaped convex portion are also formed. A second multilayer thin film is independently formed in the same order in the stacking direction up to the thin film layer directly above the active layer, and a thin film having a conductivity type opposite to that of the substrate is formed directly above the first multilayer thin film. And a thin film having the same conductivity type as that of the substrate is formed on the second multilayer thin film. 2. A double heterostructure including an active layer on the convex portion and a region other than the convex portion by a metalorganic vapor phase epitaxial growth method on a substrate of one conductivity type having a stripe-shaped inverted mesa convex portion. Are independently formed up to the thin film layer directly above the active layer, and a thin film showing the same conductivity type as that of the substrate is grown on the uppermost layer on the double heterojunction, and Zn diffusion is performed.
A method of manufacturing a semiconductor laser device, wherein only a region of the uppermost layer directly above the convex portion is a thin film layer having a conductivity type opposite to that of the substrate. 3. A double heterostructure including an active layer on the convex portion and a region other than the convex portion is formed on the one conductivity type substrate having the stripe-shaped inverted mesa-shaped convex portion by a molecular beam epitaxial growth method. The thin film layer directly above the active layer is formed independently, and a thin film having the same conductivity type as that of the substrate is grown on the uppermost layer on the double heterojunction, and by Zn diffusion, directly on the convex portion of the uppermost layer. A method of manufacturing a semiconductor laser device, wherein only the region is a thin film layer having a conductivity type opposite to that of the substrate.