JPH0325037B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a GaAs/GaAlAs buried surface emitting laser oscillation device, and particularly a structure in which the area of the active layer is smaller than the area of the cladding layer. In addition, we have made it possible to reduce the oscillation threshold current by reliably forming a current confinement layer that utilizes the reverse bias of the pn junction with good reproducibility.
The present invention relates to a method for manufacturing a GaAs/GaAlAs embedded surface emitting laser oscillation device.

[Prior Art] FIG. 2 shows an example of a conventional surface emitting laser. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type GaAs substrate, and 2 is an n-type GaAs substrate.
3 is a GaAs active layer, 4 is a p-type GaAlAs cladding layer, 5 is a reflective surface, 6 is an electrode, 7 is a mirror electrode, 8 is a current, 9 is an active region, 1
0 represents an optical resonance path, and 11 represents a laser beam.

The illustrated device allows current 8 of a predetermined level or higher to flow between electrode 6 and mirror electrode 7.
An active region 9 is generated in the GaAs active layer 3 to form a Fabry-Perot resonator between the reflective surface 5 and the mirror electrode 7. As a result, optical resonance occurs along the optical resonance path 10, and laser light 11 is emitted.

[Problem that the invention seeks to solve]

In the conventional surface emitting laser exemplified above, the gain region is only as long as the thickness of the active layer, so the oscillation threshold current density is high, and the current spread in the p-type cladding layer and the fractional carrier in the active layer increase. Since there is a large amount of leakage current that does not contribute to oscillation due to diffusion, the threshold current becomes high, and continuous operation at room temperature is difficult due to heat generation.

In order to reduce the oscillation threshold current, the threshold current density must be lowered or the area of the active region must be reduced. There are two ways to lower the threshold current density: forming a reflector with a high reflectance, or increasing the gain region by thickening the active layer, but the former has the problem of significantly decreasing laser light output. However, even in the latter method, the thickness of the active layer is limited to less than the carrier diffusion length.

[Means for solving problems]

This invention solves the above-mentioned problems and allows surface-emitting lasers to operate with a lower oscillation threshold current than conventional systems by reducing the area of the active layer relative to the area of the cladding layer. I was able to do it.
In addition, a buried structure is introduced that allows a current confinement structure to be reliably formed with good reproducibility.

〔Example〕

FIG. 1 is a cross-sectional view of one embodiment of a surface emitting laser based on the present invention, in which 12 is an n-type GaAs substrate, 13 is an n-type GaAlAs (X _AL =0.4) cladding layer,
14 is a p-type GaAlAs (X _AL = 0.4) current blocking layer;
15 is n-type GaAlAs (X _AL = 0.4) layer, 16 is p-type
GaAs active layer, 17 p-type GaAlAs (X _AL = 0.3) split layer, 18 p-type GaAlAs (X _AL = 0.45) cladding layer, 19 P ⁺ -GaAlAs cap layer, 20
is a p-side electrode such as Au/Zn/Au, 21 is Au/Ge
22 is an Au reflective film, 23 is an optical resonance path, 24 is a current, and 25 is a laser beam.

The manufacturing process of the structure shown in FIG. 1 is as follows () to (). Note that this step is illustrated correspondingly to FIG.

() In the first crystal growth, 13, which forms a DH structure,
After epitaxially growing layers 16, 17, 18, and 19, 1 is etched by chemical etching or the like.
Layers 7, 18, and 19 are etched into a cylindrical shape. (Fig. 3) Then, a second liquid phase growth is performed. (Figure 3~) () First, using the selective meltback method that takes advantage of the fact that the smaller the _Al composition ratio
Active layer 16 is selectively meltbacked. (FIG. 3) () Then, the area around the active layer 16 is filled with a p-type GaAlAs (X _AL =0.4) current blocking layer 14.
(Figure 3) () Furthermore, select meltback is performed and the p-type
Melt back the GaAlAs (X _AL =0.3) split layer 17. (Figure 3) () After that, the surrounding area is filled with n-type GaAlAs (X _AL =0.4) 15. (Figure 3) () Finally, the GaAs substrate 12 is etched,
The epitaxial surface serving as a reflecting mirror is exposed, and the electrodes 20, 2 are
The processing process ends after forming the first grade. (Fig. 3) As shown in Fig. 3, this laser forms a constriction-shaped mesa structure by the selective meltback method.
This is a buried laser with enhanced current confinement function.
Therefore, heat dissipation is excellent. In addition, a new p-type
By providing the GaAlAs (X _AL = 0.3) split layer 17 between the p-type cladding layer 18 and the active layer 16, the current confinement structure
It is formed by the reverse characteristic of p-n junction, so
It has been further strengthened.

Furthermore, conventionally, when forming a current confinement structure with a pnpn structure, it was necessary to finely control the film thickness during the second crystal growth, but in this laser, p-type GaAlAs (X _AL = 0.4)
Even if the layer thickness of the current blocking layer 14 is slightly different, by selectively melting back the split layer 17, a current confinement structure can be reliably formed.

[Comparison with conventional method]

Figure 4 shows a structural diagram of a buried mesa-constriction-type (BCM) GaAlAs laser reported by NEC Corporation. The features of this laser are as follows.

() Selective GaAlAs by chemical etching
This is a mesa stripe laser in which the active layer is etched to make the width of the active layer narrower than the width of the cladding layer.

() The current confinement structure forms a pnpn structure by utilizing a characteristic peculiar to liquid phase growth in which the growth of the p-type GaAlAs current blocking layer is completely stopped in the depression.
Incidentally, in a surface emitting laser that resonates light in the film thickness direction, the thickness of the active layer needs to be several tens of times thicker than that of a normal striped laser. For this reason, crystal growth occurs on both sides of the active layer, and it is impossible to stop the growth of the p-type GaAlAs current blocking layer in the recess like in the BCM laser described above, and it is impossible to form a pnpn current confinement structure. It becomes possible.

In such a case, it is effective to form a pnpn structure by providing a split layer and selectively melting back this layer as in the present invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, the oscillation threshold current can be significantly lowered compared to conventional surface emitting lasers, and a highly reliable surface emitting laser can be realized. In addition to the excellent features of conventional surface emitting lasers such as monolithic resonator fabrication, single longitudinal mode operation due to short resonator structure, narrow emission angle, and two-dimensional array formation, the surface emitting laser according to the present invention has the following advantages: It has high reliability due to low threshold operation, and is expected to be widely used in constructing future optical integrated circuits.
It has extremely important significance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a surface emitting laser according to the present invention, FIG. 2 is a sectional view of a conventional surface emitting laser, and FIG. 3 is an explanation showing the manufacturing process of the embodiment shown in FIG. 1. 4 are sectional views of a conventional example for explaining the effects of the present invention. In the figure, 12 is an n-type GaAs substrate, 13 is an n-type
GaAlAs (X _AL = 0.4) clad layer, 14 is p-type
GaAlAs (X _AL = 0.4) current blocking layer, 15 is n
16 is a p-type GaAlAs active layer, 17 is a p-type GaAlAs (X _AL = 0.3) layer _, 18 is a p-type GaAlAs (X _AL = 0.45) cladding layer, 19 is P ⁺
-GaAlAs cap layer, 20 is a p-side electrode such as Au/Zn/Au, 21 is an n-side electrode such as Au/Ge, 2
2 is an Au reflective film, 23 is an optical resonance path, 24 is a current,
25 represents a laser beam.

Claims (1)

[Claims] 1. After epitaxially growing the split layer 17, cladding layer 18, and cap layer 19 on the active layer 16, the split layer 17, cladding layer 18, and cap layer 19 are etched into columnar shapes, and then the active layer 16 is selectively etched. After that, the active layer is filled with a current blocking layer 14, and then the split layer 17 is selectively melted back and the area around the split layer 17 is filled with a material having a type opposite to the p/n type of the split layer 17. , active layer 16
GaAs/GaAlAs buried surface emitting laser oscillation characterized by forming a current confinement structure between the split layer 17 and the cladding layer 18 using the reverse bias characteristics of the pn junction of the split layer 17, which is smaller in area than the cladding layer 18. Method of manufacturing the device.