JPS62249497A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain the best semiconductor laser device as the device for an optical disk which has excellent noise characteristics and no non-point astigmation by a method wherein, when a stripe shape light emitting region is formed in an active layer, recessed parts are provided in the parts of a substrate which correspond to the end surfaces of the stripe and the center part of the stripe is made to be flat. CONSTITUTION:Recessed parts 2 are provided in an N-type GaAs substrate 1 by selective chemical etching. After that, an N-type GaAlAs cladding layer 3, an undoped active layer 4, a P-type GaAlAs cladding layer 5 and an N-type cap layer 6 are successively made to grow. Then a P<+>type region 7 is formed by selective Zn diffusion and an Mo-Au electrode 8 and an AuGeNi-Au electrode 9 are evaporated. After that, the laminated structure is cleft along the one-dot chain line in the figure to form a reflective surface. In the cross section near the end, a recessed part is formed also in the active layer above the recessed part 2 and difference in level of refrative index is produced between the inside of the stripe and the outside edge part by those recessed parts and a laser beam is confined. Therefore, non-point astigmation can be suppressed. Moreover, as the active layer has no difference in level in the device cross section inside the stripe, the normal narrow stripe laser structure is obtained and the laser oscillates multimode oscillation and noise of returning light can be eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser, and in particular, a semiconductor laser having no astigmatism.
This invention relates to an element with good noise characteristics.

[Conventional technology]

The structure of the conventional low-noise, low-aberration laser device is described in "Ribbed Optical Waveguide" in Proceedings 30a-M-8 of the 31st Annual Conference of the Japan Society of Applied Physics (March 29 - April 2, 1980, 41 III). As described in "Characteristics of Mode Filter Type GaAΩAs Laser", it has a composite guide structure in which a refractive index guide and a gain guide structure are connected in cascade in the axial direction of the resonator, but such a device has a stability problem. It had the problem of being chipped.

[Problem that the invention seeks to solve]

In a so-called refractive index waveguide element in which the laser light distribution (transverse mode) of a semiconductor laser is confined by the difference in refractive index between the center portion and the 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 mode becomes multiple and no return optical noise occurs, 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 t1. 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.

That is, an object of the present invention is to provide a semiconductor laser for an optical disk with good noise characteristics and no astigmatism.

[Means for solving problems]

In the present invention, when forming a striped light emitting region 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 flattened, so that the central part of the stripe is made flat. A means is provided in which the refractive index difference is small between the stripe end face portion and the outer edge portion, and the refractive index difference is large between the stripe end face portion and the outer edge portion.

[Effect]

As described above, in order to solve the above-mentioned problems, the present invention has made possible a low-noise, low-aberration laser by the technical means described below.

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.

Therefore, a gain-guided laser structure can achieve low noise in the center of the active layer, and a refractive index-guided laser structure can achieve low aberrations near the active layer end facets, resulting in a high-performance, low-noise, low-aberration laser. can do.

〔Example〕

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

Example 1 Fig. 1 is a plan view showing a recess provided in a substrate, and Figs. 2 and 3 are cross-sectional views taken along line A-A' and B-B in Fig. 1.
'It is a line cross-sectional view. First, an n-type GaAs substrate 1 is etched by selective chemical etching to a depth of 0.05 to 0.3 μm as shown in FIG.
An intermediate portion 2 is provided between the two. After this, as shown in Figure 2, the n-type G
aA Q As cladding layer 3, undoped active layer 4 (thickness 0.04 to 0.05 μm) + P-type GaA Q As cladding layer 5. An n-type cap layer 6 is sequentially grown. Next, a p small region 7 is formed by a selective Zn diffusion method, and M o
-Au electrode 8 and AuGeNj -Au electrode 9 are deposited. Thereafter, folds are formed according to the dot-dash line in FIG. 1 to form one 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 confined by this, resulting in a non-conventional condition. Point aberration is small.

In order to make the refractive index step large enough, the recess step should be 0.0.
5-0.3 pm, active layer thickness 0.04-0.05 μm,
The thickness of the n-type cladding layer is preferably 1.5 to 2 μm. In addition, the stripe width is 5 to 10 μm at the end surface part of the recess 2.
By setting it as, it becomes 3-5 micrometers.

Figure 3 is a cross-sectional view of the device 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. 6 In addition, the thickness of each layer is p-type. Layer 5 is 1.5-2 μm, n
The mold cap layer 6 has a thickness of 0.3 to 0.5 μm. A of each layer
QAs composition is 35% to 55% for layers 3 and 5, and 5% to 55% for layer 4.
It is 20%.

In this device, the longitudinal mode is multi-mode, and the relative noise intensity is I x 10-13Hz regardless of the amount of returned light.
Met. 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 in a p-type substrate 1, and a p-type GaA Q As cladding layer 3. Undoped active layer 4. n-type GaA Q As cladding layer5. n-type GaAs
After providing the cap layer 6, a p region 7 is provided by a selective Zn diffusion method, and then an AuGeNi-Au electrode 8°Mo
-A u electrode 9 was deposited. As in Example 1, after forming the folds according to the dashed line in Figure 1 and forming a reflective surface, the laser element was assembled and oscillated, and the astigmatism was as small as 5 μm or less, and the relative noise intensity was also low regardless of the amount of returned light. ,
A laser with low noise and low aberration of less than L x 10-1 aHz-'' was obtained.

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. In FIGS. 6 to 8, 11 is an n-type cladding layer or an n-type cladding layer, 12 is an n-type graded refractive index layer,
Alternatively, it is a p-type graded refractive index layer, and 13 has a thickness of approximately 0.
14 is a p-type graded refraction S$ layer or an n-type graded refraction S$ layer, and 15 is a P-type cladding 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 was explained as GaAΩAs/GaAs, but other materials such as InGaAsP
Similar effects can be expected with /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, and as a result, (1) there is no astigmatism and (2) low return light noise can be realized.

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

[Brief explanation of drawings]

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 cross sections taken along line AA' in FIG. 1 of the semiconductor laser device. Figure 1 is a sectional view taken along the line BB'. 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. ]-...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, 11.15-p, n cladding layer, 1
2.14・p. Early 1st day

Claims (1)

[Claims] 1. In a semiconductor laser in which a shallow recess is formed in a semiconductor substrate and multiple semiconductor layers including an active layer are stacked so as to fill the recess, the active layer except for the vicinity of at least one light emitting end face. 1. A semiconductor laser device characterized in that the active layer is formed flat and has a recess in the same shape or similar shape to the recess formed in the substrate in the vicinity of at least one light emitting end face. 2. In the semiconductor laser device according to claim 1,
The depth of the recess provided in the substrate is 0.05 to 0.3 μm,
A semiconductor laser device characterized in that the active layer thickness 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 molecular beam growth or vapor phase growth.