JPH0716080B2 - Semiconductor laser - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor laser that can be used for optical communication or optical erasing / recording / reproducing. More specifically, it emits visible light in the 0.6 μm band. Single lateral mode A
The present invention relates to a GaInP-based semiconductor laser.

Conventional technology As a light source for information processing devices such as digital audio discs, optical disc files, and laser printers.
Attention is focused on 6 μm band AlGaInP / GaAs semiconductor lasers. The semiconductor laser constructed by this system not only contains Al, which is easily oxidized, but also its conventional liquid phase epitaxial method (LPE method) makes it difficult to grow epitaxially due to thermodynamic limitation. In addition, it is necessary to strictly control the solid-phase ratios of the group III elements Al, Ga, and In in the clad layer and the active layer, respectively, so as to be lattice-matched with GaAs as the substrate. There are various restrictions.

Therefore, in the conventional AlGaInP-based semiconductor laser, a so-called refractive index guide structure in which a light absorption layer is provided on the upper surface of the active layer has been attempted in order to obtain the uniformity of the transverse mode.

Hereinafter, the conventional AlGaInP-based semiconductor laser described above will be described with reference to the drawings.

FIG. 2 shows the structure of a conventional AlGaInP semiconductor laser. n-type (Al _0.4 Ga _0.6 ) _0.5 In on n-type GaAs substrate 1
_0.5 P clad layer 11, non-doped Ga _0.5 In _0.5 P active layer 5, n
A type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P cladding layer 12 was sequentially epitaxially grown by a metal organic chemical vapor deposition method (MOVPE method). Next, the n-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer 12 was etched by ordinary photolithography to provide a SiO ₂ mask so as to leave about 0.2 μm with a sulfuric acid-based etchant, and then the SiO ₂ mask was used. Selectively P-type Ga
After burying in the As light absorption layer 13 and epitaxially growing the n-type GaAs cap layer 14, electrodes 8 and 9 were formed on the p-side and the n-side. The P-type GaAs light absorption layer 13 is one in which current confinement and formation of a waveguide are performed at the same time.

Problems to be Solved by the Invention In the structure of the semiconductor laser in which the transverse mode is controlled by the refractive index guide of the conventional example described above, when etching the cladding layer on the upper side of the active layer, etching control must be performed so as to leave an extremely thin layer. Therefore, there is a large variation in the thickness of the remaining layer, and the reproducibility of the semiconductor laser characteristics is poor.

Furthermore, since the second or third epitaxial growth is performed with the Al-containing layer exposed on the surface, crystal defects are introduced at the growth interface, which deteriorates the characteristics of the semiconductor laser.

Therefore, the present invention aims to solve the above problems at the same time, and to provide a single mode AlGaInP based semiconductor laser having good characteristics with good reproducibility.

Means for Solving the Problems The technical means of the present invention for solving the above problems has a bandgap larger than that of a material to be an active layer on a GaAs substrate on which a groove is formed in advance and a refractive index smaller than that of the material. Al _x Ga
_{The 1-y} As layer is formed so as to be flat on its upper surface, and then a double hetero structure composed of (Al _y Ga _1-y ) _0.5 In _0.5 P is laminated. In this case, the Al _x Ga _1-x As layer has a thickness sufficient to confine light to the active layer in cooperation with at least the (Al _y Ga _1-y ) _0.5 In _0.5 P clad layer in the groove. The GaAs substrate functions as a light absorption layer outside the groove.

Action The action of the present invention is as follows.

Since Al _x Ga _1-y As is almost lattice-matched to GaAs in the range of AlAs composition ratio x = 0 to 1, it can be easily formed on the groove formed on the GaAs substrate, and its crystallinity does not matter. . So Al _x G
If the upper surface of the a _1-x As layer is flattened, the crystallinity of the double heterostructure stacked thereon will not be impaired. In addition, the Al _x Ga _1-x As layer has a band gap larger than that of the active layer and a refractive index set to be small, and is thick enough to confine light in the concave groove. If they are thinly laminated, carrier and light can be sufficiently confined.

In addition, AlGa can be formed by one-time growth and has good characteristics easily.
InP semiconductor lasers can be obtained with good reproducibility.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a structural diagram of a semiconductor laser according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is an n-type GaAs substrate, on which a groove 2 is formed by ordinary photolithography and chemical etching. The depth and width of the groove 3 are each 1μ
m, 5 μm. n on the n-type GaAs substrate 1 by MOVPE method
A type Al _0.75 Ga _0.25 As layer 3 is grown to make the surface flat even on the groove. At this time, the thickness on the groove 3 is 1.3 μm. Then n-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer 40.1
μm, non-doped Ga _0.5 In _0.5 P layer 50.1 μm, P type (Al _0.4 G
a _0.6 ) _0.5 In _0.5 P clad layer 60.8 μm, n-type GaAs cap layer
71.5 μm is grown sequentially. After that, a Zn diffusion layer is provided to confine the current, and the n-side and P-side electrodes 8 and 9 are formed.

The Al _0.75 Ga _0.25 As layer has a larger bandgap than the Ga _0.5 In _0.5 P active layer and does not absorb light. The Al _0.75 Ga _0.25 As layer functions as a light confining layer because it has a small refractive index.

The composition of each layer shown in the example of FIG. 1 is not limited to this, and the composition of the (Al _y Ga _1-y ) _0.5 In _0.5 P double heterostructure and the Al _x Ga _1-x As layer is not limited to this. Any combination is possible, and the current confinement can be achieved by providing a GaAs current confinement layer on the GaAs substrate. Needless to say, the same effect can be obtained by using a P-type GaAs substrate.

EFFECTS OF THE INVENTION As described above, according to the present invention, an Al _x Ga _1-x As layer having a larger bandgap and a smaller refractive index than the active layer is provided adjacent to the cladding layer, so that a single-mode Al Ga layer can be easily formed.
An InP-based semiconductor laser can be obtained, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a sectional view of an AlGaInP-based semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional AlGaInP-based semiconductor laser. 1 ... n-type GaAs substrate, 2 ... concave groove, 3 ... n-type Al _0.75 Ga
_0.25 As layer, 4 ... n type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer, 5 ... undoped Ga _0.5 In _0.5 P active layer, 6 ... P type
(Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer, 7 ... n type GaAs cap layer, 8 ... n side electrode, 9 ... p side electrode, 10 ... Zn
Diffusion layer, 11 ... n type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer, 12 ... p type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer, 13
... n-type GaAs light absorption layer, 14 ... p-type GaAs cap layer.

Claims (1)

[Claims] 1. A GaAs substrate having a groove, an Al _x Ga _1-x As layer formed so as to fill the groove and have a flat upper surface, and an Al _x Ga _1-x As layer formed on the Al _x Ga _1-x As layer ( Al _y Ga _1-y ) _0.5 In _0.5 P comprising a first clad layer, an active layer and a second clad layer, the Al _x Ga _1-x As layer having a band higher than that of the active layer. A semiconductor laser with a large gap and a small refractive index.