JPS6254990A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce an astigmatism by increasing the exciting intensity of laser light at the periphery from the center of a stripe in a region near one emitting end and the intensity largest at the center of the stripe in the region except the emitting end. CONSTITUTION:An N-type Ga1-xAlxAs clad layer 2, a P-type Ga1-yAlyAs active layer 3, a P-type Ga1-xAlxAs clad layer 4 an P-type GaAs cap layer 6 are sequentially formed on an N-type GaAs substrate 1. Then, a striped region 9 remains, and proton is implanted to a region 10. Thereafter, a Cr-Au electrode 7, an AuGeNi-Au electrode 8 are deposited, and an element is separated. Since a current flows in a stripe shape except a region near the right end of the element, it is of gain waveguide type. However, since the wavy surface becomes curved and no current flows at the center of the stripe in the region near the right end, a gain distribution becomes of reverse waveguide structure. Thus, a noise is small in a longitudinal multimodes, and small astigmatism in a semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor laser for optical disks, and particularly to an element with low noise and small astigmatism.

[Background of the invention]

Semiconductor lasers for optical disks have low noise and
A gain waveguide element that performs multi-mode oscillation, in which an element with small astigmatism is desirable, has a drawback of low noise but large astigmatism. To alleviate this, Mamina et al., G.A. Applied Physics, Vol. 56, p. 3116, 1984 (T.
et al, J, Appl, Phys, Vol.
56P3116.1984) reports a structure in which the stripe width is narrowed near the end face in a gain waveguide element. However, even with this, the astigmatism is still 10 μ
m or more, and as it is, it is unsuitable as a light source for optical disks.

[Purpose of the invention]

An object of the present invention is to provide a semiconductor laser that is optimal as a light source for an optical disc.

[Summary of the invention]

The outline of the present invention will be explained using FIGS. 1 and 2.
The figure is a cross-sectional view of a gain waveguide element, in which there is no refractive index difference in the vicinity of the active layer 3 in the direction parallel to the layer.

In such a laser, the transverse mode is confined by the gain distribution 12, and the refractive index distribution is anti-waveguide as shown in 13. , Therefore, it is easy to oscillate in a contracted multimode, but the wavefront becomes curved and astigmatism becomes large. Also, as shown in Figure 2, if two electrodes are provided and a current is applied.

The gain distribution and refractive index distribution are as shown in Fig. 2 12 and 13 respectively.If laser oscillation occurs at the center of the element, the gain will be anti-guided and the refractive index guided structure. I considered it. Therefore, the wavefront is curved in the opposite direction to that shown in FIG. 1, and it is thought that astigmatism occurs in the opposite direction to that of the element shown in FIG. Based on the above considerations, it was discovered that if both regions are provided in the optical axis direction within the same element, the astigmatism cancels out and becomes extremely small, resulting in longitudinal multi-mode oscillation. It has been found that an element with small astigmatism can be implemented.

[Embodiments of the invention]

Examples of the present invention will be described below.

Example 1 This example will be explained using FIGS. 3 to 5. n-type GaAs
n-type Gaz-J Q on substrate 1 (thickness ~ 100 μm)
xAsAs Clara 2 (x=0.45. Thickness 2p
m), P-type Gat-yA Q yAs active layer 3 (y=
0.14. thickness 0.08 μm), P type Gaz-xA Q
xAsAs Clara 4 (X=0.46. Thickness 2μ
m), a P-type GaAs cap layer 6 (thickness 1 μm) was sequentially grown.

After that, protons are implanted into the region 10 to a depth of 3 μm, leaving the striped region 9. After this, the Cr-Au electrode 7
, where the AuGaNi-Au electrode 8 is deposited and separated into devices, except for the area near the right end face of the device, where current flows in a striped pattern as shown in FIG.

It is a gain waveguide type. Therefore, it oscillates in longitudinal multimode, resulting in low noise. However, the wavefront is curved. On the other hand, in the region near the end surface of the cloth, as shown in FIG. 5, no current flows at the center of the stripe, so the gain distribution becomes an anti-waveguide structure. If this region is not too long, laser oscillation will occur at the center of the stripe, so that the wavefront will be curved in a direction that cancels out the curved wavefront that occurs outside this region. As a result, the wavefront becomes flat at the right end surface, and astigmatism becomes small. The stripe width of region 9 is 2 to 8 μm,
The spacing between stripes in the area near the right end face is 2 to 5 μm.
, the length of this region in the optical axis direction is the length of the entire element 250
μm, it was 20 to 80 μm. At this time, the astigmatism of the laser beam emitted from the right end surface was as small as 2 to 8 μm.

Example (2) This example will be explained using FIGS. 6 to 8. n-type GaAs
Area 1 is left on the substrate (thickness ~100 μm), leaving area 9.
0. After that, only near the right end face of the element,
Grooves 11 are provided by chemical etching. After this, as in FIGS. 3 to 5, the n-type Get-xA n xAa cladding layer 2
．． P-type Gat-yA 11 yAs active layer 3. P-type Ga
z-xA Q
- Deposit Au electrode 8 and cut into elements.

In this element, current flows only in region 9 except near the right end face, and the element becomes a gain waveguide type. On the other hand, in the area near the edge of the cloth,
Since no current flows in the center of the stripe, the structure becomes an anti-waveguide structure in terms of gain, but the active layer is curved due to the groove 11 provided in the substrate, resulting in a refractive index waveguide structure. Due to both of these effects, the wavefront becomes flat near the right end surface, and astigmatism becomes small. The width of region 9 was 2 to 5 μm, the interval between stripes in the region near the right end face was 2 to 5 μm, and the width of groove 11 was 3 to 5 μm. At this time, the astigmatism of the laser beam emitted from the right end surface was 0 to 5 μm.

〔Effect of the invention〕

According to the present invention, a semiconductor laser with vertical multimode, low noise, and low astigmatism can be realized.

In the examples, GaA nAs-based materials were used, but it goes without saying that other materials can be used as well. Striped structures can also be created using not only proton implantation and Zn diffusion.
Naturally, structures using other methods are also effective.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a gain-guided laser, and a diagram showing the gain and refractive index distribution. FIG. 2 is a cross-sectional diagram when two electrodes are provided, and a diagram showing the gain and refractive index distribution. Figure 3 shows
The plan view of the proton implantation part, Figure 4, is Figure 3 A-A.
5 is a sectional view taken along the line B-B' in FIG. 3, FIG. 6 is a plan view of the substrate surface, FIG. 7 is a sectional view taken along the line A-A' in FIG. FIG. 6 is a sectional view taken along the line B-B'. DESCRIPTION OF SYMBOLS 1... Substrate, 2, 4... Clad layer, 3... Active layer, 6... Cap layer, 7, 8... Electrode, 9...
Striped area, 10...area, 11...groove.

Claims (1)

[Claims] 1. In a semiconductor laser in which laser oscillation occurs in a fundamental mode in a striped manner, in a region near at least one emission end face, the excitation intensity of the laser light is greater in the peripheral region than in the central region of the stripe; A semiconductor laser device characterized in that in the region, the excitation intensity of the laser beam is highest in the central portion of the stripe. 2. In the device according to claim 1, a refractive index waveguide structure having the highest refractive index at the center of the stripe is formed in the vicinity of the output end face of the laser beam, and in other regions, the refractive index waveguide structure has the highest refractive index at the center of the stripe. A semiconductor laser device characterized in that the difference in refractive index between the front and peripheral portions is smaller than that near the end face, or zero, or the refractive index is lower in the central portion.