JPH0531836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface-emitting semiconductor laser device, and more particularly to an improved structure for improving the performance of a surface-emitting semiconductor laser device.

[Conventional technology]

FIG. 4 shows a schematic configuration of a conventional surface-emitting semiconductor laser device of this type.

That is, in the conventional configuration shown in FIG. 4, numerals 2 and 3 are n-type and p-type AlGaAs layers, and 4 is a p-type GaAs layer between these layers as an active layer.
Layer 5 is an i-type AlGaAs layer for current blocking, and may be a multilayer AlGaAs layer including a reverse bias pn junction. Also, 10
is a semi-insulating GaAs substrate for forming each of the above layers, and a circular etching hole 11 is formed in order to avoid absorption of light.
0 and 31 are n-type and p-type electrodes.

Therefore, in the case of this conventional configuration, by applying a predetermined voltage to both the n-type and p-type electrodes 30, 30, and 31, the p-type
Carriers are injected into the GaAs layer 4 to generate laser gain, and the upper and lower crystal interfaces form a resonator to perform laser operation, and the output is transmitted through the etching hole 1.
On the other hand, in order to cause laser oscillation at a low current level, a mirror 100 made of dielectric or metal is formed on the lower surface of the etching hole 11 to increase the reflectance. This is also being done.

Here, in the case of this configuration, the conditions for the laser oscillation are: gl−αL−1/2ln1/R ₁ R ₂ =0 ∴g=gain, α=loss, R ₁ R ₂ = reflectance at both ends of the resonator , l=thickness of active layer, L=resonator spacing. In order to oscillate with a low threshold current, it is necessary that the value of α is small, and the value of l is extremely large, as well as the values of R ₁ and R ₂ are large. is important.

[Problem that the invention seeks to solve]

However, in the conventional configuration shown in FIG. 4, the current flows between the layers 2, 3, and 4 in the vertical direction, that is, in the vertical direction in the figure. This causes a distribution in the injected carriers, and there are sufficient carriers near the p-n junction and a high gain, but as you move away from the p-n junction, there are fewer carriers and the gain decreases. Or, it becomes a negative value. In this case, even if the thickness l of the active layer is increased, the actual value of l cannot be increased. Therefore, in the case of this conventional example configuration, The problem was that an extremely large current was required for laser oscillation, and pulse operation was barely possible at room temperature.

This invention was made to solve these problems in the conventional device configuration.
The purpose is to provide this type of surface-emitting semiconductor laser device which can increase the substantial value of l and can operate at a low enough current to perform CW oscillation at room temperature.

[Means for solving problems]

In order to achieve the above object, the present invention includes a first semiconductor layer of a first conductivity type formed on a semiconductor substrate; a first active layer having a second conductivity type with a narrow band width; a first active layer formed on the first active layer and having a wider forbidden band width than the first active layer;
a second semiconductor layer of a conductivity type, a second active layer formed on the second semiconductor layer and having a second conductivity type with a narrower forbidden band width than the second semiconductor layer; a multilayer structure semiconductor layer formed on the semiconductor substrate and having at least a third semiconductor layer of the first conductivity type having a wider forbidden band width than the second active layer; The formed first conductivity type impurity diffusion region and the second conductivity type impurity diffusion region formed on the semiconductor substrate so as to be adjacent to the multilayer structure semiconductor layer on the opposite side to the first conductivity type impurity diffusion region. an impurity diffusion layer; a first conductivity type electrode selectively formed on the first conductivity type impurity diffusion layer; and a first conductivity type electrode selectively formed on the second conductivity type impurity diffusion layer. The active layer is characterized by having an electrode of the second conductivity type, so that a current can be uniformly passed through the active layer.

[Effect]

That is, in this invention, a plurality of active layers of a first conductivity type are alternately sandwiched between semiconductor layers of a second conductivity type to form a multilayer structure semiconductor layer, and a current can be uniformly passed through the active layers. Therefore, the value of l, which is the equivalent substantial thickness of the active layer, can be increased.

〔Example〕

Hereinafter, one embodiment of a surface-emitting semiconductor laser device according to the present invention will be described in detail with reference to FIGS. 1 to 3.

FIG. 1 is a perspective view showing the general structure of the apparatus of this embodiment, and FIG. 2 is a sectional view taken along the line shown in FIG.

Also in the device configurations in the embodiments shown in FIGS. 1 and 2, reference numeral 10 denotes a semi-insulating GaAs substrate;
is a circular etching hole formed in the substrate 10 to avoid absorption of light; 1 is a p-type AlGaAs/GaAs multilayer quantum well layer as an active layer; 2 is an n-type AlGaAs layer; These layers 1 and 2 are formed in multiple layers on the substrate 10.

That is, p-type AlGaAs/
Each layer of the GaAs multilayer quantum well layer 1 is alternately sandwiched between the n-type AlGaAs layers 2 and further laminated in multiple layers, forming a p-n junction shown by a bold line. 1 and 2 are thin, for example, each having a thickness of about 0.1 to 0.2 μm, but by laminating them into multiple layers, the thickness of the entire multilayer can be increased, for example, about 20 layers. If so, it can be formed to a thickness of several μm,
As a result, the actual thickness l of the active layer itself can be increased.

In addition, the active layer 1 is not necessarily a multilayer quantum well layer as described above, but a single layer of AlGaAs.
Alternatively, a GaAs active layer can be used, and even if the thickness of each active layer is set to about 0.5 to 1.0 μm, the carrier distribution will not become very large.
In this case, the value of the actual thickness l of the active layer can be further increased, for example, to about several tens of micrometers.

Therefore, the multilayer structure of the p-type AlGaAsGaAs multilayer quantum well layer 1 and the n-type AlGaAs layer 2, which are formed in an alternating multilayer structure on the substrate 10 as described above, is then processed from the surface side. , n-type and p-type impurities are separately and selectively diffused to form n
Type and p-type impurity diffusion regions 20 and 21 are respectively formed, and at this time, the n-type impurity is, for example, Si, and the p-type impurity is, for example,
Zn can be used.

Here, when the active layer has a multilayer quantum well structure, Ga and Al atoms move mutually in the region where impurities are diffused due to the so-called disorder effect, and the atoms in the same region move. The quantum well structure collapses,
If the AlGaAs layer has an average composition and has a single-layer active layer structure, there is no change in the crystal composition in the diffusion region, but there is no particular change in its operation.

Then, n-type and p-type electrodes 30 and 31 are respectively provided on predetermined portions of the surfaces of these n-type and p-type impurity diffusion regions 20 and 21, and electrodes 30 and 31 are provided in order to take out the emitted light from the substrate 10 side. An etching hole 11 is formed, and although not shown in the figure, it is possible to provide a dielectric layer or a metal layer on the upper and lower surfaces of the crystal in order to increase the reflectance.
This is exactly the same as the conventional structure.

In the case of the device configuration in the embodiments shown in FIGS. 1 and 2, by applying a predetermined voltage to both the n-type and p-type electrodes 30 and 31, p-
A carrier is injected through the n-junction. and,
In this case, as is clear from the cross-sectional structure of FIG. It consists of part b,
For the former, a heterojunction with AlGaAs and GaAs or a multilayer quantum well layer is used, and for the latter,
Each consists of a homojunction of AlGaAs,
The former has a lower diffusion potential due to its narrower forbidden band width than the latter, so most of the current flows to the former junction, only a small amount flows to the latter junction, and the current is injected into the active layer. carrier (in this case,
Regarding the ratio of carriers flowing outward (holes in this case) to electrons, the number of carriers flowing toward the narrow side increases as the forbidden band width becomes narrower.

Therefore, most of the applied current is carried by carriers (electrons in this case) injected into each active layer, which is effective for the gain caused by recombination in each active layer. It will contribute to
Furthermore, since the potentials applied to each active layer are structurally almost the same, the amount of carriers injected into each active layer does not change, and as in the conventional structure,
There is no gain reduction due to carrier distribution that occurs when a thick single-layer active layer is used, and the gain in this example structure is proportional to the number of active layers x the thickness of each active layer. and the value of the above-described substantial thickness l of the active layer can be increased,
In principle, it is possible to increase the gain by increasing the number of active layers.

In addition, in the structure of the embodiment described above, in order to limit the laser emission part to a part of the crystal, as in the structure shown in FIGS. 1 and 2, or the structure shown in FIG. 3A as another embodiment, Each electrode 30, 31 is formed only on a part of the surface of the impurity diffusion regions 20, 21, and by utilizing the effect of the bulk resistance, a means is taken to flow current only in the vicinity of each electrode 30, 31. Alternatively, if the active layer 1 has a multilayer quantum well structure, by utilizing the increase in the p-n junction diffusion potential where the diffusion portions are in contact with each other due to the above-described disordering, as in the structure shown in FIG. In addition, it is possible to take measures such as leaving the non-diffused portion in a circular shape, and further, as shown in the structure shown in FIG. 3c, the electrodes 30 and 31 may be arranged concentrically. .

In the above embodiment, for convenience of explanation, a case has been described in which a GaAs/AlGaAs-based material is used as the semiconductor material, but similar actions and effects can be obtained with other semiconductor materials.
For example, it may be an InP/InGaAsP material,
In this case, since the InP of the substrate becomes transparent to the oscillation light, there is no need to form etching holes on the substrate surface as in the case of the GaAsAlGaAs-based material. Furthermore, in the configuration of the embodiment, n
It is clear from the above description that even if the type and p-type impurity diffusion regions are reversed, there is no change in the operation and effect.

〔Effect of the invention〕

As described in detail above, according to the present invention, on a semiconductor substrate, a plurality of active layers of a first conductivity type are connected to each semiconductor of a second conductivity type having a wider forbidden band width than the active layer. The layers are alternately sandwiched to form a multilayer structure semiconductor layer, and from the surface side of this multilayer structure semiconductor layer,
By selectively diffusing impurities of the first and second conductivity types to form impurity diffusion regions of the first and second conductivity types, carriers can be uniformly injected into the active layer from the upper and lower layers. As a result, it is possible to set the equivalent substantial active layer thickness l to a large value, thereby increasing the gain and creating a surface-emitting semiconductor laser device with low current operation sufficient for CW oscillation at room temperature. It can be constructed and accomplished.

In addition, the electrodes are selectively formed and their shapes are made small, so even if the active layer is striped,
The light emitting area of the laser can be made as small as a few micrometers in the form of a spot.

Moreover, it has excellent features such as being relatively simple in structure and easy to implement.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an outline of a surface-emitting semiconductor laser according to the present invention, FIG. 2 is a cross-sectional view of the line taken along the line shown above, and FIGS. 3 a to 3 c are plan views of different examples of the above, respectively. Further, FIG. 4 is a sectional view showing a general configuration of the above-mentioned device according to a conventional example. 1... p-type AlGaAs/GaAs multilayer quantum well layer as an active layer, 2... n-type AlGaAs layer, 10...
Semi-insulating GaAs substrate, 11... etching hole in substrate, 20... n-type impurity diffusion region, 21...
p-type impurity diffusion region, 30...n-type electrode, 31...
...p-type electrode.

Claims (1)

[Scope of Claims] 1. A first semiconductor layer of a first conductivity type formed on a semiconductor substrate; a first semiconductor layer formed on the first semiconductor layer and having a narrower forbidden band width than the first semiconductor layer; a first active layer having a second conductivity type; a second semiconductor layer of the first conductivity type formed on the first active layer and having a wider forbidden band width than the first active layer; a second active layer formed on the semiconductor layer and having a second conductivity type with a narrower forbidden band width than the second semiconductor layer; a multilayer structure semiconductor layer having at least a third semiconductor layer of a first conductivity type having a wider forbidden band; and a multilayer structure semiconductor layer of a first conductivity type formed on the semiconductor substrate so as to be adjacent to the multilayer structure semiconductor layer. an impurity diffusion region; a second conductivity type impurity diffusion layer formed on the semiconductor substrate so as to be adjacent to the multilayer structure semiconductor layer on a side opposite to the first conductivity type impurity diffusion region; a first conductivity type electrode selectively formed on the first conductivity type impurity diffusion layer; and a second conductivity type electrode selectively formed on the second conductivity type impurity diffusion layer. What is claimed is: 1. A surface-emitting semiconductor laser device, characterized in that it has a type electrode.