JPS5932076B2 - Semiconductor laser device and its manufacturing method - Google Patents

Description

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

Various proposals and prototypes of single transverse mode oscillation semiconductor lasers have been made so far.

By narrowing the stripe width of the active layer and confining only the lowest order transverse mode of light, single mode oscillation becomes possible. The most typical single mode oscillation laser structure is a buried stripe structure as shown in FIG.
The manufacturing method of this structure is to form an n-type G
al-xAlxAs2, n-type GaAs active layer 3, p-type G
Al-xAtxAs4 and p-type GaAs5 were grown sequentially,
Next, a VCSi02 film is applied and formed into stripes, and mesa etching is performed using the VCSi02 film as a mask to form a grown layer in the form of stripes. Thereafter, a buried layer 6 having a wider forbidden band width and higher specific resistance than the active layer is grown. Finally, the ohmic electrode T is formed to complete the process. However, in this manufacturing process, it is necessary to attach a striped VCSi02 film as a mask to prevent the buried layer from growing above the stripes. During the growth of the buried layer, the SiO2 film and the vicinity of the active layer are left in close contact with each other at high temperatures, so stress is applied to the active layer due to the difference in thermal expansion coefficient between the SiO2 film and the GaAs layer, causing deterioration. . Furthermore, impurities that form deep energy levels are used to increase the resistivity of the buried layer, but these impurities diffuse and invade the active layer, causing deterioration of characteristics. Recently, in order to overcome these problems with buried stripe type lasers, single mode oscillation has been developed using new structures.

An example of its configuration is shown in FIG. The manufacturing method is to deposit n-type Gal-XAtXAS on a grooved n-type GaAs substrate 8.
9, n-type GaAs active layer 10, p-type Gal-XAtXA
Sll and p-type GaAsl2 are grown sequentially, and S is deposited on the surface.
Attach the iO2 film 13 and place it opposite to the grooved position.
Open a window in the form of a 13VC strip of O2 film. Thereafter, an ohmic electrode 14 is formed to complete the process. During growth, the first layer n-type Gal-
The structure is such that it passes through the XAtXAS layer 9 and is absorbed by the n-type GaAs substrate 8, and single mode oscillation is possible in the active layer in the groove.

However, in this structure, the active layer 10 is flat, and the light generated in the active layer in the groove portion easily propagates and spreads in the lateral direction, so that the oscillation mode is distorted in the lateral direction.

Regarding heat dissipation characteristics, in the former buried stripe type, the active layer is surrounded by a high-resistance layer with poor thermal conductivity, which results in poor heat dissipation, and in the latter case, current is limited by an insulating film. Therefore, it does not exhibit good heat dissipation characteristics to the heat sink.

The present invention provides a new structure that has excellent heat dissipation characteristics and realizes single mode oscillation, unlike the above structures, and a method for manufacturing the same. The present invention will be described below based on examples together with drawings.

Step-like steps are formed on the n-type substrate 15 as shown in FIG. 3a.

Using this as a substrate, as shown in FIG. 3b, an n-type clad layer 16, a non-doped active layer 17, a p-type clad layer 18,
An n-type current limiting layer 20, which can be selectively etched, is continuously grown on the ohmic electrode forming layer 19 and the fourth layer 19, and an insulating film 21 is attached thereon. Striped windows will be opened in the area. Using the insulating film 21 with the opening as a mask, the n-type current limiting layer 20 is removed by selective etching, and after contact diffusion is performed on the p-type ohmic electrode forming layer 19 that appears in a stripe shape, the insulating film 21 is removed. is removed to produce a structure as shown in FIG. 3c. Next, a p-type ohmic electrode 22 and an n-type ohmic electrode 23 are sequentially provided to produce a laser device as shown in FIG. 3d. In this structure, the first cladding layer 16 is made thick enough that the light leaking from the active layer 17 is not absorbed by the substrate 15 at the step portion, and extremely thick at the portion other than the step portion so that the light is absorbed by the substrate 15. By making the active layer 17 thinner, it can suppress the spread of light by providing the same effect as the structure shown in FIG. It has the characteristics of being able to

By shortening the length between the bends of the active layer 17, only the lowest-order transverse mode light is confined, and stable single mode oscillation can be obtained. Moreover, heat dissipation is achieved by not using an insulating film as the current limiting layer, but by using the current limiting layer 20, which has higher thermal conductivity than the insulating film and has a coefficient of thermal expansion that is not different from that of the fourth layer p-type ohmic electrode forming layer 19. Characteristics can be improved. A specific example of a method for manufacturing a single mode oscillation semiconductor laser having this new structure will be described below.

GaAs, Gal-XAlxAs on n-type GaAs substrate
A single mode oscillation semiconductor laser constructed by

100 of the VCn-type GaAs substrate 15 as shown in FIG.
11 which is the cleavage plane of the substrate by chemical etching on the plane
A step of 1 μm is formed perpendicular to the 0 plane.

Next, a first layer n is formed on the surface by liquid phase epitaxial method.
Type Gal-XAlxAsl6 at flat part 0.2 μm~2nd layer non-doped GaAsl7 0.1 μm13rd layer p-type Gal-XAlx'Asl8 1.5 μm14th layer p-type GaAsl9 1 μm15th layer n-type Gal- YAtyA
S2O is continuously grown to 1 μm.

Subsequently, a Si3N4 film 21 is applied to the surface, and striped windows with a width of 5 .mu.m are formed in correspondence with the positions of the steps on the substrate, thereby producing the structure as shown in FIG. 3b. Next, Si3N4 film 2
1 as a mask, the fifth layer n-type Gal-YAtyAS2O
etching. At this time, hydrochloric acid, phosphoric acid, or a mixture thereof is used as a selective etching solution so that etching is stopped at the fourth p-type GaAsl layer 9. Subsequently, zinc is diffused onto the surface of the fourth layer p-type GaAsl9 exposed in a stripe pattern, and then the Si3N4 film 21 is removed to form the structure shown in FIG. 3c.
form like this. Next, as shown in FIG. 3d, p-type electrode metal is vacuum-deposited and alloyed to form the p-side ohmic electrode 22. Further, a metal for an n-type electrode is vacuum-deposited on the substrate side, and an alloying process is performed to form an n-side ohmic electrode 23. Finally, the device is separated into element pieces, the p-side electrode 22 is adhered to a heat sink, and a gold wire is connected on the n-side electrode metal film 23 to complete the process. GaAs-Ga produced in this way
The l-XAtxAs semiconductor laser operated in single mode continuous wave operation at room temperature and exhibited excellent heat dissipation characteristics.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a laser with a buried stripe structure, FIG. 2 is a cross-sectional view of a laser constructed on a grooved substrate, and FIGS. 3a-d are fabrication of an embodiment of the present invention. It is a process cross-sectional view of a method. 15...n-type GaAs substrate, 16...
n-type Gal-AtXASll7... n-type Ga
Asll8...p-type Gal-o'Alx'As
ll9...p-type GaAsl2O...n
Type Gal-YAtyASl2l...Si3N4
Film, 22...P-side electrode metal film, 23...
・N-side electrode metal film.

Claims (1)

[Scope of Claims] 1. An active layer is formed on a semiconductor substrate having a step on its main surface, with a cladding layer interposed therebetween, so that the active layer is inclined with respect to the main surface at the step, and is identical to the semiconductor substrate. conductive type,
A current limiting layer having stripe-shaped openings is formed at a position facing the sloped portion of the active layer, and the sloped portion forms a striped active region, and the cladding layer allows light to pass through the semiconductor substrate at the stepped portion. 1. A semiconductor laser device having a thickness such that light is not absorbed by the semiconductor substrate, and a thickness such that light is absorbed by the semiconductor substrate in areas other than the stepped portion. 2. A step of forming a step on the surface of the semiconductor substrate, and forming a cladding layer on the semiconductor substrate to a thickness such that light is not absorbed by the semiconductor substrate in the step portion, and that light is not absorbed into the semiconductor substrate in areas other than the step portion. a step of forming an active layer on the cladding layer so as to be inclined with respect to the main surface at the stepped portion; forming a current limiting layer having a striped opening at a position facing the sloped portion of the semiconductor laser device.