JPS62296487A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To concentrate an applied current at a projection efficiently by interrupting a current flow forming a reverse bias junction internally by setting a current constriction layer grown selectively in a region except the projection in a different electric conduction type from that of a substrate or the first clad layer. CONSTITUTION:A stripe like projection of definite height and width is formed along a specific crystal axis on the surface of a semiconductor substrate 1 by a photoetching technique, a semiconductor layer 2 which has different conductivity from that of the semiconductor substrate is provided except the region of the stripe like projection for a current constriction layer and covering these, the first clad layer 3, an active layer 4 and the second clad layer 5 are formed in sequence by epitaxial growth. The semiconductor layer 2 for the current constriction layer is set to have as different conductivity type from that of the substrate 1 or the first clad layer 3 and a reverse bias junction is formed internally for interrupting a current flow.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a semiconductor laser, and more particularly, to a current confinement structure of a semiconductor laser.

BACKGROUND OF THE INVENTION Semiconductor lasers are ideal as light sources for optical fiber communications and optical disks due to their excellent features such as small size, high efficiency, and long life, and their applications in these areas have already begun.

Recently, they have been actively used in consumer electronics such as compact discs, and the demand for them is rapidly increasing.

In order to apply semiconductor lasers to the various applications mentioned above, firstly, in order to improve the focusing ability of the laser beam and the coupling efficiency to optical fibers, etc., it is necessary to stabilize the transverse mode in the direction parallel to the junction. It must be controlled to have a single peak shape, and secondly, it is necessary to introduce a current confinement limiting layer or the like so that the injection current is effectively supplied to the laser active region.

FIGS. 4 to 6 are sectional views of main parts showing representative examples of striped structures that have been proposed so far. FIG. 4 shows a structure in which a double heterojunction formed by an active layer 14 and a cladding layer 18 is etched to leave a stripe shape, and then this is embedded with a low refractive index current confinement layer 15 with a wide forbidden band width. Yes, it is called an embedded hetero-stripe structure. In contrast, FIG. 5 shows a buried crescent stripe structure in which a current confinement layer 15 is grown on a substrate 17, a striped groove is formed, and a double heterojunction is formed in the groove by second epitaxial growth. . In addition, FIG. 6 shows an isometric refractive index optical waveguide and a plano-convex waveguide stripe structure in which the thickness of the optical guide layer 19 adjacent to the active layer 14 is changed by grooves formed in the substrate 17. Concentration is
This is due to the formation of the high concentration region 16 by thermal diffusion. In each structure, the laser active region 14 becomes an optical waveguide surrounded by a low refractive index medium, and transverse mode control and stabilization are achieved.
The current path is restricted by the high concentration diffusion region 16 and the high concentration diffusion region 16. Through such efforts, highly reliable and highly efficient semiconductor lasers have come to be realized, and the application to the above-mentioned law field is the result of the above-mentioned improvement efforts.

Problems to be Solved by the Invention In the conventional technology represented by FIGS. 4 to 6, in order to realize the above structure, multiple epitaxial growths or high-temperature processes such as thermal diffusion are required. The manufacturing process was becoming more complex. In order to manufacture a semiconductor laser with excellent characteristics, the thickness and width of each layer must be precisely controlled, and complicating the process causes a significant decrease in yield.

Additionally, during the epitaxial growth and thermal diffusion process of the current confinement layer, diffusion of added impurities and thermal damage to the already grown regions may occur.
These also cause a loss of reliability. As mentioned above,
The conventional structure is insufficient to mass-produce elements with high reliability and excellent characteristics, and there is a need for a new structure to solve the above-mentioned problems.

Means for Solving the Problems The present invention provides a striped convex portion on a semiconductor substrate, and firstly restricts the current path to only areas other than the above-mentioned convex portions during epitaxial growth on the semiconductor substrate. A semiconductor layer having a conductivity type different from that of the substrate is grown to form a current confinement layer, and then a first cladding layer, an active layer, and a second cladding layer are grown sequentially over the entire surface to form a double heterostructure. It is a joint.

According to the present invention, a reverse bias junction is formed inside by setting the current confinement layer selectively grown in a portion other than the convex portion to have a different electrical conductivity type from that of the base and the first cladding layer. The flow of current can be blocked, thereby
Injected current can be efficiently concentrated on the convex portion. Furthermore, if a semiconductor material having a refractive index different from that of the first cladding layer is used as the current confinement layer, the equivalent refractive index for the optical mode guided by the active layer can be changed between the convex portion and the other portions. It is possible to control the transverse mode in the direction parallel to the pn junction.

Embodiment FIG. 1 is a sectional view of a main part of an embodiment of the present invention, in which a surface portion of a semiconductor substrate 1 having a predetermined conductivity type is etched at a predetermined height along a specific crystal axis by a well-known photolithography technique. A striped convex portion having a length and a width is formed, and a semiconductor layer 2 having a conductivity different from that of the semiconductor substrate is formed in a portion other than the striped convex portion.
are provided to serve as a current confinement layer, and a first cladding layer 3. is formed to cover these layers. The active 7 layer 4 and the second cladding layer 5 are sequentially formed as epitaxially grown layers. The semiconductor layer 2 serving as the current confinement layer is set to have a different conductivity type from both the base body 1 and the first cladding layer 3, and forms a reverse bias junction therein to function to prevent current flow.

FIG. 2 is a sectional view of a main part of another embodiment of the present description, in which a semiconductor layer as a current confinement layer is formed into two layers having different forbidden band widths.
1.22.

In this case, the first semiconductor layer 21 is used for current limiting, and the second
The semiconductor layer 22 is used for controlling the transverse mode of laser oscillation,
Highly efficient and unimodal fundamental mode oscillation characteristics can be achieved.

In Figure 3, the active layer is InGaAsP and the base is InP.
FIG. 2 is a cross-sectional view of an embodiment of a so-called long wavelength semiconductor laser.

As shown in FIG. 3, striped convex portions were formed along the <011> crystal axis direction on the P-type InP substrate 6 by chemical etching. The height is about 3 μm, and the width of the convex portion is 3 to 4 μl. In epitaxial growth,
If the melt is grown on the substrate with a very low degree of supersaturation, growth on the convex portions will be suppressed. According to experience, when the width of the convex part is less than 6 μm, depending on the growth time,
No growth was carried out on the convex part, and selective growth was possible on other parts. 1
nGaAsP (λg=1.3 μm) 8 is grown, followed by a P-type 1nP cladding layer 9. InGaAsP
An active layer (λg to 1.3 μm) 10 and an n-type 1nP cladding layer 11 were sequentially grown over the entire surface to form a double heterojunction. On the outside of the convex portion, the n-type 1nGaAsP layer 8 is close to the active layer 10 with the cladding layer 9 in between.
The isometric refractive index decreases and forms a refractive index optical waveguide with the convex portion. By appropriately selecting the thicknesses of the cladding layer 9 and the active layer 10, the transverse mode can be stably maintained in the fundamental mode. In this example, the active layer thickness was approximately 0.1 μl, and the clad layer thickness was approximately 0.4 μm.

Electrode 1 was placed on the epitaxial wafer fabricated as described above.
3, and after going through processes such as creases, assemble it on the stem,
Characteristics were measured. It was confirmed that the light emission caused by current injection was concentrated in the convex portion, and that current confinement was completely performed. Further, the oscillation threshold current value was around 40a+A, oscillation was in a single-peak fundamental mode, and the structural mode was also stable.

In the embodiment of the present invention, InGaAs with InP as a substrate is used.
Although the case of a P long wavelength laser has been shown, it goes without saying that the same effect can be obtained for other materials as long as the active layer has a combination of materials in which the forbidden band width is smaller than that of the substrate.

As described in detail, the present invention solves the problems in the prior art and can provide semiconductor lasers with excellent characteristics with good mass production. Further, the method for doing this is extremely simple and has a great advantage in that it can be easily realized. In addition, the present invention takes advantage of the characteristics of epitaxial growth; for example, growth on convex portions has a lower growth rate than on flat portions, making it possible to precisely control the thickness of the active layer and cladding layer. , which is much easier than the conventional method.

[Brief explanation of the drawing]

1 and 2 are sectional views of main parts of a semiconductor laser according to each embodiment of the present invention, FIG. 3 is a sectional view of main parts of another embodiment of the present invention, and FIGS. 4 to 6 are sectional views of main parts of a semiconductor laser of a conventional structure. It is a representative sectional view of each. 1...Semiconductor substrate, 2,21.22...
・Current confinement layer, 3...First cladding layer, 4...
...Active layer, 5...Second cladding layer, 6.
...P-1nP substrate 7゜11-- n-type 1nP,
8-- n-type 1nGaAsP. 9-.-P-1nP, 10-.-InGaAsP active layer. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1
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Claims (2)

[Claims] (1) Striped protrusions having a predetermined height and width are formed along a specific crystal axis on the surface of a semiconductor substrate having a predetermined conductivity type, and the semiconductor substrate is formed in a portion other than the striped protrusions. What is claimed is: 1. A semiconductor laser comprising a semiconductor layer having a conductivity type different from that of the first cladding layer and a double heterostructure comprising a first cladding layer, an active layer, and a second cladding layer. (2) The semiconductor laser according to claim 1, wherein the semiconductor layer is composed of two or more semiconductor layers having different forbidden band widths.