JPS5957487A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To manufacture a multimode laser with small non-spot astigmation by a method wherein a clad layer near the end of laser beam emitting channel of a gain guide type laser is made thicker near the stripe type current supplying region and thinner distant from the region providing the clad layer with a waveguide filling the effective role of refractive guide. CONSTITUTION:Before starting epitaxial growing operation, an N type GaAs substrate 1 is preliminarily etched by mask and etching solution excluding the part directly below the stripe type current supplying region so that the part A with specified length near the end is made thicker than the remaining region i.e. forming a groove 9 with a concave section. When an N type AlxGa1-xAs clad layer 2 is epitaxially grown on such an N type GaAs substrate 1, the grown surface becomes almost flat when the clad layer 2 is completely grown. Therefore the thickness of said layer 2 is thicker at the A part near the end directly below the stripe becoming thinner at both sides. The non-spot astigmation of the gain guide type laser may be improved by means of providing the part A near the end of a laser resonator with said structure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain guide type semiconductor laser device that oscillates in longitudinal multimode, and particularly to a structure for improving astigmatism thereof.

In recent years, the development of semiconductor laser devices has been remarkable, and in particular, not only transverse single mode oscillation of various stripe structures with refractive index guides, but also longitudinal single mode oscillation (hereinafter referred to as single mode oscillation) have been realized, and semiconductor laser devices have been used for reading optical disk memories. It is now reaching the practical stage in fields such as digital audio discs (digital audio discs, etc.) and communications. However, single mode oscillation has problems such as noise being easily generated due to the interference of the returning light to the laser itself, and significant mode competition noise occurring during longitudinal mode transitions due to temperature changes.
Particularly in the field of consumer equipment such as video discs and audio discs, which are used over a wide temperature range, it is said that semiconductor lasers with longitudinal multimode oscillation, which are less susceptible to these phenomena, are more suitable than single-mode lasers. ing.

On the other hand, various narrow stripe-shaped lasers without a refractive index guide are known as semiconductor laser structures that emit multimode oscillation. However, in such a narrow striped laser, the light is guided by a gain guide in the direction parallel to the active layer (hereinafter referred to as a gain-guided laser), so the wavefront of the light is curved and the wavefront is bent in the direction parallel to the active layer. Compared to the laser light pressure that spreads out in different directions, the virtual radiation position differs, which is what is called astigmatism. videotask, digital audio disc (
This astigmatism is undesirable for applications such as 1) AD) in which laser light is focused by a t-lens. This is because if there is astigmatism, a special lens such as a cylindrical lens must be used to effectively focus the light. Moreover, even if a cylindrical lens is used, astigmatism slightly depends on the manufacturing conditions of the element and has poor reproducibility, so it is necessary to prepare lenses of various standards, and in fact, it is difficult to use a cylindrical lens. It was difficult to compensate for astigmatism.

This invention was made in view of the above points, and the cladding layer near the end face of the laser light emission path of a gain-guided laser is made thick near the striped current injection region and thinned away from the stripe. By providing a waveguide that effectively functions as a refractive index guide, the objective is to provide a multimode laser with small astigmatism. The present invention will be explained below based on the drawings.

FIG. 1 is a perspective view showing a semiconductor laser device according to an embodiment of the present invention, in which 1 is an n-type gallium arsenide (GaAs) substrate, 2, 3, and 4 are the n-type GaAs substrates, respectively.
A first layer is laminated on the main surface of the substrate 1 using a liquid phase epitaxial growth technique: an n-type AlxGa1-, As cladding layer, a p-type AIyGa,-yAs active layer, and a p-type Alx
Ga, -x A, s cladding layer, n-type Alx
Ga+-xAs rad layer 2 and p-type AlxGa,-,
The refractive index of the As cladding layer 4 is p-type A ly G a
The values of X and y are selected to be sufficiently smaller than the refractive index of the H-y As active layer 3, forming a double heterostructure. Here, the feature of this invention is that n-type Qa A
Before epitaxial growth, the s-a plate 1 is prepared by removing the area immediately below the striped current injection part, and forming a part (A in the figure) near the end face with a certain length of the n-type GaAs substrate 1, which is thicker than the remaining area. A predetermined mask (
In this way, an n-type Al %
In epitaxial growth, the growth rate of the n-type A IxGa, -XAs cladding layer 2 has a characteristic that the crystal growth is generally faster in the four parts and slower in the convex parts. At the end of the process, the growth surface becomes almost flat.

Therefore, the thickness of the n-type A I X G ;+1-x A S cladding layer 2 can be made thicker in the vicinity of the end face, directly under the stripe, and thinner on both sides thereof.

In this invention, as described below, by providing such a +i structure near the end face of the laser resonator, the astigmatism of the gain guide type laser can be improved. 5 is an n-type Ga formed on such a double heterostructure
A 8 layer 8 is a groove formed by etching the n-type GaAs105Y stripe up to the p-type AlxGa, -X, As cladding layer 4, and the position of this groove 8 is directly in line with the groove 9 at the edge of the substrate. Ten pressure is located. 6 is a p+ diffusion layer in which KZn is diffused over the entire surface including the inside of this groove 8, 7 is a p-side electrode, and 1° is an n111] electrode.

In this embodiment, when a voltage is applied between the n-side electrode 1 and the n-side electrode 1° so that the former has positive polarity, the area other than the bottom of the striped groove 8 is p−n −− Since it acts as a p-structured current blocking layer, current flows concentrated only directly under or in the vicinity of the striped grooves 8. At this time, the electron has a mouth shape A I y Ga 1-
In the S cladding layer 2, the holes are p-type Alx oa,
-, As cladding layer 4 to p-type Al, Ga I-, A
s is injected into the active layer 3, and light emission occurs due to recombination of electrons and holes. It is well known that in such a structure, if the current is increased sufficiently, gain-guided laser oscillation will occur in which light is guided by the gain distribution in a direction parallel to the p-type AlyGa+ -yAs active layer 3. It is being In general, if the stripe width is made narrow enough (for example, 5 μm or less), the oscillation mode can become single mode in the transverse mode and multimode in the longitudinal mode (it is known that this type of gain guide type As mentioned above, astigmatism is seen in the oscillation of , and since the astigmatism has poor reproducibility, it would be better to eliminate this astigmatism or to adjust it to a certain value with good reproducibility. It is difficult to put multimode lasers into practical use, which has the advantage of low noise.

Therefore, in the present invention, after forming an IK groove 9 in an n-type GaAs substrate near the end face of a laser beam emission path of a gain-guided laser, as shown in the part in FIG.
Form A IX Qa I-! By growing the As cladding layer 2, the cladding layer 2 is given a thickness distribution, and a waveguide is provided which effectively functions as a refractive index guide.

FIG. 2 schematically shows how light seeps out from the p-type AlyGaI-yAS active layer 3 in a cross section perpendicular to the junction surface in the part shown in FIG. 1B. n in the outer part of the groove 9 of the n-type GaAS substrate 1 (the part marked with a square in FIG. 2)
Type A I
a 1-y A The light seeping out from the A S active layer 3 is an n-type G a A with large absorption, as shown in 11 in Fig. 2.
Reach the S substrate 1 and be affected by the refractive index of the n-type GaAs substrate 1. The refractive index of the n-type QaAs substrate 1 is n-type A.
1xGa I-x A, which is larger than the refractive index of the s cladding layer 2, and has large light absorption (n-type Al
Since the bandgap of the aH-XAS cladding layer 2 is larger than that of the p-type Al, OA, -Y As active layer 3), a kind of refractive index guide is likely to be formed in this part. Become.

FIGS. 3(a) and 3(b) show the waveguide portion A of the present invention.
is a plan view schematically showing the effect of improving astigmatism when viewed from a direction perpendicular to the active layer surface, and FIG.
FIG. 3(b) shows the wavefront of the laser beam and the spread of the light in the vicinity of the resonator end face in the embodiment of the present invention. As can be seen from FIG. 3(a), in the conventional gain-guided laser, the wavefront (indicated by the broken line in the figure) gradually curves near the cavity end face, and the p-type AlyGa+ -YAs active layer 3 Since the light confinement effect in the horizontal direction is weak, the light emitted from a considerable depth of the end face also contributes as laser light, so the laser light appears to be emitted from the depth of the resonator end face by a distance li++i d. However, in the structure of the above embodiment of the present invention, as shown in FIG. 3(b), the light entering the waveguide portion A from the gain guide type laser portion B is refracted by the waveguide portion A as described above. It acts as a rate guide and has a light confinement effect, and n-type GaA
Since the light leaking into the s-substrate 1 is absorbed, it does not spread near the end face, and the laser light is transmitted near the end face (d' in the figure).
It appears to be radiated from.

On the other hand, since the light is guided by a double heterostructure refractive index guide in the direction perpendicular to the three surfaces of the p-type A1yGal-yAs active layer, the laser light source position is at the resonator end surface pressure. The positions of the radiation sources in the vertical and horizontal directions with respect to the p-type At, oa, -y As active layer 31C are almost the same,
Astigmatism almost disappears. In addition, the waveguide part A
If the length is too long, the mode will become close to vertical oscillation mode or single mode, which will increase the noise, so it is better to make it as short as possible. However, if the length is too short, the guide effect will be lost, and the minimum length of about 20 μm to 30/Am is required because of the accuracy in forming a mirror surface by cleavage.

In addition, in the above embodiment, GaAs AlGaAs
Although examples using InP (indium phosphide) and InGaAsP (indium gallium arsenic phosphorous) based quaternary compounds have been shown, it goes without saying that the present invention can also be applied to semiconductor lasers using quaternary compounds such as InP (indium phosphide) and InGaAsP (indium gallium arsenic phosphorus). Further, the present invention can also be applied to semiconductor lasers having a gain guide type stripe structure other than those using the current narrowing method using grooves as in this embodiment. Further, in the above embodiment, for the sake of simplicity, the waveguide guide is provided only on one end face of the laser resonator, but it is of course possible to provide the waveguide guide on both sides.

As explained above, the semiconductor laser device according to the present invention provides a waveguide guide having a structure in which the cladding layer near the cavity end face of the semiconductor laser is thick immediately below the striped region and thin in the region other than the striped region. Since this is not provided, astigmatism can be reduced to a minimum, and therefore, if this invention is used, the mode transition noise during temperature changes will be reduced, resulting in multi-mode oscillation! This is an extremely effective way to realize a practical gain-guided laser that is free of astigmatism while keeping the Samurai's characteristics intact.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an embodiment of the present invention, and Fig. 2 is a sectional view perpendicular to the joint surface of the human part in Fig. 1. Schematic diagram, Figure 3 (a)
, (b) is a diagram showing that the waveguide portion of the present invention improves astigmatism, and (a) is a diagram showing the wavefront of laser light and light near the resonator end face in a conventional gain guide type laser. FIG. 3B is a diagram showing the wavefront of laser light and the spread of light in the embodiment of the present invention. In the figure, 1 is an n-type Ga AS substrate, 2 is an n-type Al x
Ga, -. As cladding layer, 3 is p-type A ly G a H-y
AS active layer, 4 is p-type Atxoa, -1As cladding layer, 5 is n-type GaA 8 layer, 6 is p+ diffusion layer, 7 is pall TL pole, 8 is formed by etching n-type QaAs*Y 9 is a groove in the substrate in a waveguide portion, 10 is an n-side electrode, A is a waveguide portion, and B is a gain guide type laser portion. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Makoto Kuzuno - (1 other person) Figure 1 Figure 2 - 43'; Figure 3 (a) Hand line, correction i4F C spontaneous)''4':'+
': Mr. Director-General of Fl Agency 1, 1'1.
7-170051 2, Invention? , Name Semiconductor laser device 3.1 Yamamasa - Name (GOI) Mitsubishi type (Group 1, Company representative Kata 111 Jinhachibe 4, Agent note Address 1.1, Marunouchi, I-ku, Chiyo, Tokyo Nicho I
I Z Sound 33S5, Section 4 of Claims of Specification Subject to Amendment 1) and Section 1 of Claims; C Detailed Explanation Column 6, Contents of Amendment (1) The scope of claims of the specification as attached. Make amends. (2) “The cladding layer 2j is [
n-type A LX Ga1-xAsAs Clara 1ζ layer 2 tuyere 1+ru. (3) Similarly, “Figure 1 B” on page 7, line 14 is changed to “Figure 11
Figure A”. 1゜2, 4; Persimmon claimed by Ir 1NJ, a double-hetero drawing in which a surrounding active layer is sandwiched between crat layers with a larger band cap and a lower refractive index ii9
In a gain-guided double heterojunction semiconductor laser having a structure in which carriers are intensively injected into narrow stripe-like regions of two active layers, two The thickness of at least one of the two cladding layers near one or both of the end faces in the direction perpendicular to the striped region surface is set to be 4I thick in the vicinity of the striped region and thick in other regions. A semiconductor laser device ν1゜ characterized in that it is provided with a waveguide whose thickness is reduced.

Claims (1)

[Claims] The active layer has a thicker band cap (2) with a double heterostructure sandwiched by crat layers with a lower refractive index.
Concentrated in narrow stripe-like tfI regions of two active layers =
In a Geitz-guided double-i1 junction semiconductor laser having a structure in which V rays are injected, the resonator of this semiconductor laser is n? The thickness distribution t in the direction perpendicular to the striped region surface of at least one of the two cladding layers near one or both of the two end faces of the striped region is thick in the vicinity of the striped region and thick in other regions. 1. A semiconductor laser device comprising a waveguide that is thinner in a region.