JPH0564477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser device.

Conventional configurations and their problems In recent years, semiconductor lasers that oscillate in a fundamental transverse mode at a low threshold have been required as light sources for writing and reading information into DADs, optical disk files, etc., and as light sources for optical communications. ing. One effective means to achieve this is to use double growth to incorporate a built-in current constriction mechanism (internal stripe) into the structure of the semiconductor laser. FIG. 1 shows a cross-sectional view of an example of a conventional semiconductor laser using internal stripes. This conventional semiconductor laser will be explained below with reference to the drawings.

In Figure 1, 1 is a p-type GaAs substrate, 2 is an n-type GaAs substrate, and 2 is an n-type GaAs substrate.
3 is a p-type Ga _1-x Al _x As clad layer, 4 is a non-doped Ga _1-y Al _y As active layer, 5 is an n-type Ga 1-x Al x As clad layer, and 6 is an n-type Ga _1-x Al _x As clad layer. An n-type GaAs cap layer, 7 an n-side ohmic electrode, and 8 a p-side ohmic electrode.

The operation of the semiconductor laser device configured as described above will be described below.

The current injected into the substrate from the p-side electrode is blocked by the current narrowing layer 2 in areas other than the groove, and therefore flows intensively into the active layer 4 directly above the groove. The light generated in the active layer by this injected current leaks into the clad layer, but the light that leaks into the first clad layer 3 is absorbed by the current constriction layer 2 on the substrate in areas other than the grooves. Therefore, light is confined only in the active layer above the groove, and stable fundamental transverse mode oscillation is obtained here.

However, as the field of application of semiconductor lasers has expanded, the demand for semiconductor lasers that can achieve not only low threshold voltage and fundamental transverse mode oscillation but also high output has rapidly increased. One of the very effective means of increasing the output power of a semiconductor laser is to grow the active layer very thinly (about 0.05 μm) and increase the leakage into the cladding layer, thereby reducing the light emission in the cross section of the semiconductor laser. This is a method of increasing the area and decreasing the optical output density per unit area.

Figure 2 shows the results of theoretical calculations. In Figure 2, the horizontal axis is the film thickness of the active layer, and the minor axis is the maximum optical output emitted from the laser edge when the optical output density leading to edge destruction is constant pd = 2MW/ ^cm3 . . As is clear from the figure, the active layer thickness is 0.1
As the thickness decreases from around 0.2 μm, the obtained light output increases significantly. However, in the structure shown in FIG. 1, since a flat active layer is grown on a flat substrate, it is difficult to control the thinning of the active layer, and the limit is about 0.1 μm. For this reason, although the structure shown in FIG. 1 is advantageous for low threshold voltage and fundamental transverse mode oscillation, it is very disadvantageous for increasing output power, and so far only an output of several mW has been realized.

Purpose of the Invention In view of the above-mentioned drawbacks, the present invention provides a semiconductor laser with a new structure that utilizes internal stripes to maintain low threshold and fundamental transverse mode oscillation while making it possible to thin the active layer and achieve high output. The purpose is to provide a device.

Structure of the Invention In order to achieve this object, a semiconductor laser device of the present invention includes at least one semiconductor layer formed on a substrate having a mesa so that the conductivity types of the semiconductor layer alternately change. The semiconductor device is characterized in that a trench is formed that reaches the semiconductor surface, and each layer including the active layer is formed as a first layer having a conductivity type different from that of the semiconductor surface layer.

With this configuration, it is possible to achieve thinning of the active layer with good reproducibility by utilizing the anisotropy of crystal growth while maintaining the advantages of internal stripes.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

3a to 3c are cross-sectional views at each step of a method for manufacturing a semiconductor laser device according to an embodiment of the present invention.

First, etching is performed on the p-type GaAs substrate 1 (100) surface to form a pattern with a height of 3 μm and a width of 15 μm as shown in Figure 3a.
Forms a mesa of m. On the substrate, an n-type GaAs current confining layer 2 is grown by liquid phase epitaxial method to a thickness of 0.8 μm on the mesa and 1 μm at the thinnest part of the flat part of the substrate other than the mesa (the 3
Diagram a).

Grooves are formed in the <011> direction on the surface of the wafer after this first growth. The groove is positioned directly above the mesa on the substrate, with the bottom of the groove reaching the substrate.

A first p-type Ga _0.57 Al _0.43 As cladding layer 3 is formed on the mesa near the groove by a thickness of about 0.2 μm, and a second non-doped Ga _0.92 Al _0.08 As active layer is formed on the grooved substrate surface again by liquid phase epitaxial method. 4 at the same location, 0.05μm,
A third n-type Ga _0.57 Al _0.43 As cladding layer 5 is successively grown at the same location to a thickness of about 1.5 μm, and a fourth n-type GaAs cap layer 6 is grown to a thickness of about 2 μm.
Thereafter, a metal for the n-side electrode is deposited and alloyed to form the n-side ohmic electrode 7. A metal for the p-side electrode is deposited on the substrate side, and an alloying process is performed to form the p-side ohmic electrode 8. (Figure 3c).

The semiconductor wafer produced in this way is cleaved and mounted on a Si block to complete the process.

The operation of the semiconductor laser device configured as described above will be described below. Due to the action of the current confinement layer formed in the first epitaxial growth, the current injected from the substrate side is intensively injected into the active layer above the groove. As a result, a fundamental transverse mode oscillation is obtained here with a low threshold. Further, due to the effect of the protrusions previously formed on the substrate, the current confining layer formed in the first epitaxial growth has a shape that trails on both sides of the mesa, as shown in FIG. 3a.
Therefore, when a second growth is performed on top of this, due to the anisotropy of crystal growth, the growth at the top of the mesa is suppressed more than at the other skirts, so it is difficult to reproducibly create an extremely thin active layer on the top of the mesa. Can be formed well.

As described above, according to this example, by forming a mesa on the substrate prior to growth, stable high output of fundamental transverse mode oscillation, threshold value of 30 mA, and optical output of 30 mW was achieved.

Note that although this example shows the case of a p-type substrate,
Exactly the same effect can be expected in the case of a molded substrate.

Effects of the Invention As described above, the present invention can achieve high output while maintaining a low threshold value and fundamental transverse mode oscillation by configuring an internal stripe type laser on a substrate having a mesa. Its practical effects are significant.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an example of a conventional semiconductor laser using internal stripes, Figure 2 is a diagram showing the results of theoretical calculations of the relationship between active layer thickness and maximum optical output, and Figures 3 a to c are from this book. FIG. 3 is a cross-sectional view of each step of a manufacturing method according to an embodiment of the invention. 1... p-type GaAs substrate, 2... n-type GaAs current confining layer, 3... p-type Ga _1-x Al _x As cladding layer, 4
...Non-doped Ga _1-y Al _y As active layer, 5...n-type
Ga _1-x Al _x As cladding layer, 6... n-type GaAs cap layer, 7... n-side ohmic electrode, 8... p-side ohmic electrode.

Claims (1)

[Claims] 1. At least one semiconductor layer is formed on a substrate having a mesa so that the conductivity type changes alternately, a groove is formed from the surface of the semiconductor layer to the mesa portion of the substrate, and an active layer is formed on the surface of the semiconductor layer. 1. A semiconductor laser device, wherein each of the layers includes a layer having a conductivity type different from that of the surface layer of the semiconductor layer as a first layer.