JPS6236888A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To perform low returning light noise by providing a waveguide region of a refractive index guide at both ends of a light emitting region, and providing a portion having the waveguide region for mainly guiding a gain at least part of the interior to generate an effect of mode filter, thereby resultantly preventing an astigmatism. CONSTITUTION:A recess 2 is formed by selective chemical etching on an N-type GaAs substrate 1. Then, an N-type GaAlAs clad layer 3, an uncoped active layer 4, a P-type GaAlAs clad layer 5 and an N-type cap layer 6 are sequentially grown. Thereafter, a P<+> type region 7 is formed by a selective Zn diffusing method to deposit an Mo-Au electrode 8 and an AuGeNi-Au electrode 9. Subsequently, it is cleaved to form a reflecting surface. A recess is also formed on the active layer above the recess 2 to produce a refractive index difference between the striped interior and the outer edge. Thus, since the laser light is enclosed in this manner, an astigmatism is small. Since no step is formed on the active layer, it becomes a normal narrow striped laser structure in multimode of laser oscillation, thereby generating no returning light noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor laser, and in particular to a semiconductor laser without astigmatism.
This invention relates to an element with good noise characteristics.

[Background of the invention]

In a so-called refractive index waveguide element in which the laser light distribution (transverse mode) of a semiconductor laser is confined by the refractive index difference between the center and outer edge of the stripe, the oscillation spectrum line (longitudinal mode) is single. When such an element is applied to an optical disk, return light noise is generated due to light reflected from the disk. On the other hand, in an element with a small refractive index difference, the longitudinal modes become multiple and return optical noise does not occur, but so-called astigmatism occurs in which the position of the beam waste is different in the vertical and parallel directions of the active layer, making it difficult to focus the laser beam. There is a drawback that there is no For this reason, an element with multi-mode longitudinal modes and no astigmatism is desired.

To achieve this, the above objective can be achieved by changing the stripe structure in the optical axis direction of the semiconductor laser, making the refractive index difference small inside the element, and increasing the refractive index difference near at least one laser beam emitting end face. be able to. Regarding such devices, Shimada has already developed a ``rib optical waveguide mode.''
Characteristics of filter type GaA Q As laser, No. 31
There are lectures on reaction products (March 29 to April 2, 1982), etc.

However, such semiconductor lasers have the drawback of lacking stability.

[Purpose of the invention]

An object of the present invention is to provide a semiconductor laser for an optical disk that has good noise characteristics and is free from astigmatism.

[Summary of the invention]

In the present invention, when forming striped light-emitting regions in the active layer, a shallow recess is provided in advance in the substrate corresponding to the end face of the stripe, and the central part of the stripe is left flat without forming a recess. , a means is provided for making the refractive index difference small between the stripe central portion and its outer edge portion, and the refractive index difference large between the stripe end face portion and its outer edge portion.

Representative examples are shown in FIGS. 1 to 3. The inside of the element has a normal narrow stripe structure. On the other hand, near the end surface, metal-organic pyrolysis (
MOCVD method) or molecular beam epitaxial method (
(MBE method), it is possible to increase the difference in refractive index between the stripe portion and its outer edge portion.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail using FIGS. 1 to 3.

□゛-, -Example 1 - Figure 1 is a plan view showing a recess provided in the substrate, Figures 2 and 3 are cross-sectional views taken along line A-A' in Figure 1 and B
-B' line sectional view. First, an n-type GaAs substrate 1 is etched by selective chemical etching to a depth of 0.05-0.3 as shown in FIG.
pm, longitudinal width 50~'1.00μm, narrow direction width 5~
A section 2 of 10 μm is provided.

Thereafter, as shown in FIG. 2, an n-type GaA Q As cladding layer 3. Undoped active layer 4 (thickness 0.04-0.05
pm).

p-type GaA Q As cladding layer5. n-type cap layer 6
grow sequentially. Next, a p+ region 7 is formed by a selective Zn diffusion method, and a Mo-Au electrode 8, an AuGe
A Nj, -All electrode 9 is deposited. Thereafter, the arms are opened according to the dashed line in FIG. 1 to form a reflective surface. Figure 2 shows a cross section near the end face, where a recess is also formed in the active layer above the recess 2, which creates a refractive index step between the inside of the stripe and the outer edge, and the laser light is trapped by this, making it non-reactive. Point aberration is small. In order to make the refractive index step large enough, the recess step should be 0.05 to 0.3 μm and the active layer thickness should be 0.
, 04--0, 15 pm.

The thickness of the n-type cladding layer is preferably 1.5 to 2 μm.

Moreover, the stripe width becomes 3 to 5 μm by setting the concave portion 2 to 5 to 10 μm.

FIG. 3 is a cross-sectional view of the element inside the stripe. Since there is no step in the active layer, relay laser oscillation with a normal narrow stripe laser structure becomes multi-mode and does not generate return optical noise.

The thickness of each layer is 1.5 to 2 μm for the p-type rad layer 5, and n
The mold cap layer 6 has a thickness of 0.3 to 0.5 μm. A of each layer
fl As composition is 35 to 55% in layers 3 and 5.

Layer 4 is 5-20%.

In this device, the longitudinal mode is multi-mode, and the relative noise intensity is 1.0 regardless of the amount of returned light. X 10-13Hz-
It was 1. Moreover, astigmatism was 5 μm or less.

Example 2 Next, an example in which the substrate is made of p-type GaAs will be described with reference to FIGS. 4 and 5.

First, a concave portion 2 similar to that shown in FIG. 2 is provided on a p-type substrate 1, and a p-type GaA 11 As cladding layer 3. Undoped active layer 4. n-type GaA 11 As cladding layer5. n-type Ga
After providing the As cap layer 6, p is deposited by selective Zn diffusion method.
+ region 7 is provided, then AuGeNj-Au electrode 8°M
An o-Au electrode 9 was deposited. Same as Example 1-1
After forming the folds according to the dashed line in the figure and forming a reflective surface, the laser element was assembled and oscillated, and the astigmatism was 5.
A low-noise, low-aberration laser with a relative noise intensity of I x 10-''Hz-1 or less was obtained, which was as small as μm or less, regardless of the amount of returned light.

Example 3 An example will be described in which both sides of the active layer are provided with a gradient refractive index separation and confinement structure.

FIG. 6, FIG. 7, and FIG. 8 are compositional cross-sectional structural diagrams of the active layer and its surrounding cladding layer in FIGS. 2 to 5. 6 to 8, 11 is an n-type cladding layer or a p-type cladding layer, 2 is an n-type graded refractive index layer or a p-type graded refractive index layer, and 13 is an n-type graded refractive index layer or a p-type graded refractive index layer. Thickness approx. 0
．． 01-0.02 μm undoped active layer, 14
is a p-type graded refractive index layer or an n-type graded refractive index layer, and 1-5 is a p-type rad layer or an n-type cladding layer.

By adopting such a tilted refractive index separation and confinement structure, the laser light not only exhibits low noise and low aberration characteristics, but also the laser oscillation spot diameter can be increased, so the level difference between the end face of the stripe and the inside of the stripe can be reduced. In addition to the advantage of increasing the margin, there is also the advantage of reducing the oscillation threshold current density.

In the above explanation, the material system is GaA Q As / Ga
Although explained as As-based, other materials such as InGa
Similar effects can be expected with AsP/InP and InGaP/GaAs systems.

〔Effect of the invention〕

As explained above, in the semiconductor laser of the present invention, a waveguide region of a refractive index guide is provided at both ends of the light emitting region, and a portion having a waveguide region mainly composed of a gain guide is provided in at least a part of the interior thereof. be.

In the waveguide regions of the refractive index guides at both ends of the emission region, the mode and
A filter effect is produced, resulting in (1) no astigmatism and (2) low return light noise.

Since the semiconductor laser of the present invention does not require a lens for correcting astigmatism, it is most suitable as a light source for video discs, compact discs, and the like.

[Brief explanation of the drawing]

1 to 3 are diagrams showing examples, and FIG. 1 is a plan view showing grooves provided in the base, and FIGS. 2 and 3 are 8' lines in FIG. 1 of the semiconductor laser device. It is a sectional view and a BB' line sectional view. FIGS. 4 and 5 are cross-sectional views showing the second embodiment. Furthermore, FIG. 6, FIG. 7, and FIG. 8 show Example 3.
FIG. 2 is a compositional cross-sectional structure diagram of an active layer and its surrounding area. 1...Substrate, 2...Shallow recess, 3...p (n)
Cladding layer, 4... Active layer, 5...n (P) cladding layer, 6... Cap layer, 7... Zn diffusion layer, 8
, 9... Electrode, 1.1. ．． 15...pan cladding layer, 1.2.14...p. n graded refractive index layer, 13... active layer;

Claims (1)

[Claims] 1. A semiconductor laser in which a shallow rectangular recess is formed in a semiconductor substrate, and multiple semiconductor layers including an active layer are stacked to fill the recess, except for the vicinity of at least one light emitting end face. 1. A semiconductor laser device, wherein the active layer is formed flat, and the active layer is provided with a recess in the same shape or similar shape to the recess formed in the substrate near the at least one light emitting end face. 2. In the semiconductor laser device according to claim 1,
The depth of the rectangular recess provided in the substrate is 0.05 to 0.3μ
A semiconductor laser device characterized in that the thickness of the active layer is in the range of 0.04 to 0.15 μm. 3. A semiconductor laser device according to claim 1 or 2, in which each growth layer is formed by vapor phase growth.