JPH0613713A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a highly efficient semiconductor laser device by a method wherein a beam of light is led out to a clad layer from an active layer by making small the difference of refractive index on the interface between the active layer and the clad layer, the light output is increased, and the meltback on the interface is prevented. CONSTITUTION:This semiconductor laser device is composed of an active layer 16, the first and the second clad layers 14 and 18 which are provided on both surfaces of the active layer 16 sandwiching the active layer 16, and a semiconductor substrate 11 containing a current constriction layer 12 with a stripe-like groove provided adjacent to the first clad layer 14. The semiconductor layer device is constituted in such a manner that an optical guide layer 17, having the refractive index middle of that of the active layer 16 and the clad layer 18, is provided at least on the interface between the active layer 16 and the second clad layer 18 among the interfaces of the active layer 16 and the first and the second clad layers 14 and 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, for example, an inner stripe type semiconductor laser device is constructed as shown in FIG.

That is, in FIG. 3, a semiconductor laser device 1 includes a substrate 2 made of p ^{+ -type} GaAs and an n ⁺ -type GaA.
a current confinement layer 3 made of s, a p-cladding layer 4 made of p ⁺ -type GaAlxAs, an active layer 5 made of GaAlyAs, and an n-type made of n ⁺ -type GaAlxAs doped with a group VI element such as selenium or tellurium. Clad layer 6,
and a cap layer 7 made of n ^{+ type} GaAs.

Electrode layers (not shown) are provided on the lower surface of the substrate 2 and the upper surface of the cap layer 7, respectively, and a stripe-shaped groove 8 is formed in a V shape from the upper surface of the current confinement layer 3. Beyond the boundary between layer 3 and substrate 2 said substrate 2
It is provided to reach inside. Here, the above x is selected to be larger than y.

[0005]

However, according to the semiconductor laser device 1 having such a structure, the energy level of each layer is as shown in FIG. 4, and the active layer 5 and the both sides thereof are formed. Since the energy difference between the p-cladding layer 4 and the n-cladding layer 6 located is relatively large, the difference in refractive index between the active layer 5 and the p-cladding layer 4 and the n-cladding layer 6 is large. It becomes relatively large.

As a result, the light generated in the active layer 5 does not easily exude from the active layer 5 to the p-clad layer 4 and the n-clad layer 6, and therefore the light emission spot of the semiconductor laser device 10 is prevented. Was relatively small, and it was difficult to obtain a large light output.

GaA having a relatively small Al composition ratio y
On the active layer 5 made of lyAs, an n ^{+ type} GaAlxA doped with a group VI element and having a relatively large Al composition ratio x is formed.
When liquid phase crystal growth of the n-clad layer 6 made of s is performed, meltback occurs, so that the interface between the active layer 5 and the n-clad layer 6 is roughened, and the optical output is further reduced. There was a problem that it would end up.

In view of the above points, the present invention reduces the difference in the refractive index at the interface between the active layer and the clad layer so that the light can be guided from the active layer to the clad layer, thereby increasing the emission spot. Then, it is an object of the present invention to provide an efficient semiconductor laser device by increasing the light output and preventing meltback at the interface.

[0009]

The above object is to provide an active layer,
A semiconductor including first and second clad layers provided on both surfaces of the active layer so as to sandwich the active layer, and a current confinement layer having a stripe-shaped groove provided adjacent to the first clad layer. In a semiconductor laser device consisting of a substrate,
Of the interfaces between the active layer and the first and second cladding layers,
An optical guide layer having an intermediate refractive index between the active layer and the cladding layer is provided at least at the interface with the second cladding layer, and the optical guide layer also serves as a meltback prevention layer. It is achieved by a semiconductor laser device characterized by the above.

[0010]

According to the above construction, the interface between the active layer and the cladding layers located above it, or the interface between the active layer and the cladding layers above and below it, respectively, has an intermediate refractive index between the active layer and the cladding layer. By the light guide layer having a refractive index,
Since they are isolated, the difference in the refractive index between the active layer and the light guide layer and between the light guide layer and the cladding layer becomes relatively small. Since the light generated in the active layer can be easily led out toward the clad layer, this can increase the emission spot and thus the light output.

When an n-type material other than Group VI is used as the doping material of the optical guide layer, meltback of the active layer during liquid phase growth of the second cladding layer can be prevented. This means that the Al composition ratio, the doping concentration, etc. of the active layer and the cladding layer can be selected to the optimum values, so that the electron injection efficiency can be improved, and a better efficiency can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows an embodiment of an inner stripe type semiconductor laser device constructed according to the present invention.

The semiconductor laser device 10 is a p ^{+ type} GaA.
On the surface of the substrate 11 made of s, n ⁺
After crystal growth of the current confinement layer 12 made of GaAs, a stripe-shaped groove 13 extending from the surface of the current confinement layer 12 into the substrate 11 is formed by etching or the like.

Subsequently, p ⁺ GaAl was formed by the LPE method.
p-clad layer 14 made of xAs and p ⁺ -type GaAl
a first light guide layer 15 made of zAs and GaAlyA
an active layer 16 made of s, and a second optical guide layer 17 made of n ⁺ -type GaAlzAs, selenium, consisting n ⁺ -type GaAlxAs to VI group elements is doped tellurium n
-Clad layer 18 and cap layer 19 made of n ^{+ -type} GaAs are sequentially crystal-grown.

Thereafter, the lower surface of the substrate 11 and the upper surface of the cap layer 19 are provided with electrode layers (not shown), respectively.

Here, the light guide layers 15 and 17 are made of Al.
The composition ratio z is larger than the Al composition ratio y of the active layer 16,
Further, it is selected to be smaller than the Al composition ratio x of the p-clad layer 14 and the n-clad layer 18, and the light guide layer 17 is preferably a material other than a group VI n-type material such as Si. It has been doped using.

The semiconductor laser device 10 according to the present invention comprises:
The first optical guide layer 15 is formed between the active layer 16 and the p-clad layer 14, and the VI group element is formed between the active layer 16 and the n-clad layer 18 as described above. Since the two optical guide layers 17 doped with are respectively provided, the difference in the Al composition ratio (x−x−) between the active layer 16 and the p-cladding layer 14 or the n-cladding layer 18 is obtained.
Even when y) is relatively large and therefore the difference in refractive index is large, the presence of the light guide layers 15 and 17 between them causes the active layer 16 and the light guide layers 15 and 17, and also the light guide layers. The difference in the Al composition ratio between the layers 15 and 17 and the p-clad layer 14 and the n-clad layer 18 (x
Since -z) and (z-y) are relatively small, the difference in refractive index is also small.

As a result, the light generated in the active layer 16 is easily led out from the active layer 16 through the light guide layers 15 and 17 toward the p-cladding layer 14 and the n-cladding layer 18. As a result, the light emission spot can be increased and the light output can be increased.

Furthermore, when the first optical guide layer 15 is formed on the p-clad layer 14 and when the active layer 16 is formed on the first optical guide layer 15, the active layer is also active. Even when the second light guide layer 17 is formed on the layer 16, the n-clad layer 18 is formed on the second light guide layer 17.
Even when forming a film, meltback does not occur at each interface.

Therefore, each interface is kept smooth, and the p-cladding layer 14, the active layer 16, and the n-cladding layer 18 can be selected to have optimum Al composition ratios x and y, respectively, and the doping can be performed. The concentration can also be chosen to be the optimum value.
As a result, the energy level of each layer of the semiconductor laser device 10 becomes as shown in FIG. 2, and thus the carrier injection efficiency and the confinement efficiency do not decrease and the efficiency is high. A good semiconductor laser device 10 can be obtained.

In the above embodiment, the active layer 16
Although the case where the optical guide layers 15 and 17 are provided between the cladding layers 14 and 18 located above and below, respectively, the present invention is not limited to this, and the structure in which the optical guide layer 15 is omitted is also effective. Although reduced, almost the same effect can be obtained.

[0022]

As described above, according to the present invention, the difference in the refractive index at the interface between the active layer and the clad layer is made small so that the light can be guided from the active layer to the clad layer. By increasing the light emission spot, increasing the light output, and preventing meltback at the interface, an efficient and extremely excellent semiconductor laser device can be provided.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an embodiment of a semiconductor laser device according to the present invention.

FIG. 2 is a graph showing the energy level of each layer in the semiconductor laser device of FIG.

FIG. 3 is a partial cross-sectional view showing an example of a conventional semiconductor laser device.

4 is a graph showing energy levels of respective layers in the semiconductor laser device of FIG.

[Explanation of symbols]

 10 semiconductor laser device 11 substrate 12 current confinement layer 13 stripe-shaped groove 14 p-clad layer 15 first optical guide layer 16 active layer 17 second optical guide layer 18 n-clad layer 19 cap layer

Claims (2)

[Claims] 1. An active layer, and first and second clad layers provided on both sides of the active layer so as to sandwich the active layer,
In a semiconductor laser device comprising a semiconductor substrate including a current confinement layer having a stripe-shaped groove provided adjacent to the first clad layer, among the interfaces between the active layer and the first and second clad layers. A semiconductor laser device, wherein an optical guide layer having a refractive index intermediate between those of the active layer and the cladding layer is provided at least at the interface with the second cladding layer. 2. The semiconductor laser device according to claim 1, wherein the light guide layer also functions as a meltback prevention layer.