JPS6197986A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To enable to oscillate a single transverse mode with high efficiency and in low operating current in a semiconductor laser by a method wherein the laser is constituted in the structure, wherein the clad layer on the active layer has a protruded part, and at the same time, the refractive index in the clad layer reduces as going away from the center of the active region. CONSTITUTION:An N type GaAs buffer layer 2, an N type Ga1-xAlxAs clad layer 3, a P type Ga1-yAlyAs active layer 4 and a P type Ga1-zAlzAs clad layer 5 are made to grow on the (100) plane of an N type GaAs substrate 1. Provided that, the mixed crystal ratio in the N type Ga1-xAlxAs clad layer 3 is made smaller as becoming nearer the center of the active layer. Then, a stripe is formed of a photo resist film 7 in parallel to the <011> direction of the surface 6 of an epitaxial layer and an etching is performed on the P type Ga1-zAlzAs clad layer 5. Moreover, a P type Ga1-z'Alz'As clad layer 8 and an N type GaAs current stopping layer 9 are made to grow. The P type Ga1-z'Alz'As clad layer 8 is made to grow in such a way that the refractive index in the layer 8 becomes smaller as going away from the center of the active layer and a diffusion of Zn is performed on a part thereof to form a P type GaAs region 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser device used as a light source for various electronic devices and optical devices.

Conventional Structures and Problems Low current operation and single-transverse mode oscillation are important performances required of semiconductor lasers as coherent light sources for electronic and optical equipment. In order to achieve these, it is necessary to effectively confine the laser light near the active region where the laser light propagates, and to suppress its spread so as to concentrate the current flowing through the laser element. A laser with this structure is usually called a striped semiconductor laser.

There are relatively simple striping methods that use only current narrowing, specifically those that apply proton irradiation to a planar semiconductor laser, those that perform Zn diffusion, and those that form an insulating film such as an oxide film. Examples include those that have an internal current constriction region formed by crystal growth, etc.

However, in these methods, although the confinement of laser light is weak and the spread of current is suppressed, it is difficult to say that carriers are effectively confined within the active layer by current injection.

In addition, by changing the refractive index and A-Lugieganop in the cladding layers that sandwich the active layer of a conventional planar semiconductor laser, we have effectively confined light and carriers and achieved low-current operation (RIM laser (Talaib node index laser)). ), but it is insufficient in terms of light confinement in the direction parallel to the active layer.

OBJECTS OF THE INVENTION In view of the above drawbacks, it is an object of the present invention to provide a semiconductor laser device having a stripe structure for current confinement and further having a structure that effectively confines laser light and carriers in both directions perpendicular and parallel to the active layer. .

Structure of the Invention To achieve this object, the semiconductor laser device of the present invention includes a multilayer thin film forming a double heterostructure including an active layer on a substrate, and a part of the cladding layer directly above the active layer has a convex shape. , the refractive index in the cladding layer above the active layer decreases with increasing distance from the center of the active region. With this configuration, laser light can be effectively confined within the active region by changing the refractive index and carriers can be effectively confined within the active region by changing the energy gap, thereby achieving low current operation, single-transverse mode oscillation, and highly efficient oscillation.

DESCRIPTION OF EMBODIMENTS An embodiment of the semiconductor laser device of the present invention will be specifically described with reference to the drawings.

As an example, an n q Ga As substrate (carrier concentration ~101801n, about -3) is used as the substrate. n-type Ga
As shown in FIG. 1, an n-type GaAs buffer layer 2 of 0.6p was formed on the (100) plane of the As substrate 1 by metal organic vapor phase epitaxial growth (hereinafter referred to as Mocvn method).
m + nm Ga, -xA, 5xAs cladding layer 3 11-57-(.

Ga1-yAlyAs active layer 4 (0≦y<x;
y<z) was grown to 0.05 μm, and the p-type Ga, -2A12As cladding layer 5 was grown to 0.5 μm. However, at this time,
The mixed crystal ratio in the n-type G2L1-xAlxAs cladding layer 30 was made smaller as it got closer to the active layer, and therefore the refractive index was made larger as it got closer to the active layer.

Next, the shrimp layer surface 6 was subjected to a cleaning treatment, and stripes with a pitch of 250 μm and a width of 2 μm were formed using a photoresist film 7 parallel to the <011> direction.

By H2SO4 etching for 2 nights, p-type Ga, -
z The film thickness h2 of the k12As cladding layer 5 in FIG. 2 is 0.
．． Etching was performed until the thickness was 2 μm.

Further, on the shrimp layer on the etched substrate, mo
By the cvD method, as shown in Figure 3, pzGa, -2/
k12t As cladding layer s (z≦z') in Figure 3, film thickness h2 is 1.2 μm, n-type GaAs current blocking layer is film 1, h3 is 0.8 μm, film thickness h4 is o, 4 μm. was grown epitaxially. At this time, p-type Cr&
The mixed crystal ratio in the 1-2tk12tAs layer 8 grew to increase as it moved away from the active layer, and therefore the refractive index grew to decrease as it moved away from the active layer.

Furthermore, as shown in Figure 3, Zn is diffused to form a p-type G.
a AS region 12 was formed.

The refractive index profile in the vicinity of the active region 13 of the semiconductor laser has an origin of ○ shown in FIG. 3, yR9yL, x+
, x in one direction as shown in FIG. 6 or FIG. 7, respectively. The refractive index profile of a normal semiconductor laser is shown in FIG. 4, and the refractive index 10 file of a GR N laser is shown in FIG. In this example, compared to the semiconductor laser having the refractive index profiles shown in FIGS. 4 and 5, the carriers are equal to or better in the X direction and also in the yR1yL direction perpendicular to the X direction due to the energy gap difference. Laser light can be effectively confined by a difference in refractive index. An example of crystal growth conditions for the MOCVD method is a growth temperature of 770° C., a growth rate of 8 μm/hour, a supply molar ratio of the group Ⅰ element to the group Ⅰ element of 50, and a total gas flow rate of 5β/min.

Ohmic electrodes 11° and 10 were fabricated on the p-side and n-side, respectively.

When current was injected, single-transverse mode oscillation occurred at a low threshold of 25 mA to 30 mA. A high external differential quantum efficiency of about 50% was obtained on both sides of the laser symmetry device.

It has been experimentally demonstrated that by changing the mixed crystal ratio with dense crat formation, it is possible to give the energy gap and refractive index a profile (V) that is effective for confining carriers and laser light.

In this embodiment, GaAs-based and GaJUAs-based semi-4 body lasers have been described, but the present invention is also applicable to semi-4 body lasers made of compound semiconductors containing InP threads and other multi-component mixed crystals. It is possible.

Crystal growth methods other than MOCVD, such as LPE and MBE
You may also use the law.

Effects of the Invention As described above, the semiconductor laser device of the present invention has a structure in which the cladding layer on the active layer has a convex portion and the refractive index in the cladding layer decreases as it moves away from the active region and from U. It can perform single-transverse mode oscillation with high efficiency and low current operation, and its practical effects are remarkable.

[Brief explanation of the drawing]

1, 2, and 3 are diagrams showing the process of manufacturing a semiconductor laser device according to an embodiment of the present invention, and FIGS. 4 and 5 show the refractive index of the cladding layer of a conventional semiconductor laser device. 6 and 7 are diagrams showing the refractive index profile in the cladding layer of the semiconductor laser device in this example. 1... n-type Ga As substrate, 2... n-type Ga As substrate layer, 3... n-type Ga,
-x klxAs cladding layer, 4...Ga,
-y A% As active layer, 5...p type (ra,
-2Ad2As cladding layer, 6-...pgGa, -2A
d2As cladding layer surface, 7...Striped photoresist film, 8...p 5 Ga 1
- Z/A lz t As cladding layer, 9'''
"' N-type Ga As current blocking layer, 10...n-side ohmic electrode, 11...p-side ohmic electrode, 12...Zn diffusion region or p m Ga As
Region, 13...Active region, hI I h21 h
51 h4...Thickness of each layer at each position. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 6 Refraction middle refraction cell

Claims (1)

[Claims] There is a multilayer thin film forming a double heterostructure including an active layer on a substrate, the cladding layer directly above the active layer has a convex portion, and the refractive index in the cladding layer above the active layer is different from the center of the active region. A semiconductor laser device characterized by decreasing monotonically as the distance increases.