JPS6237912B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a semiconductor laser.

There are various types of semiconductor lasers capable of fundamental transverse mode oscillation, one of which is a current confinement plano-convex laser.

Figure 1 shows an example of an InP--InGaAsP current-confined plano-convex laser using an n-type substrate. The above element is constructed by forming an n-type InGaAsP guide layer 2 whose composition is selected such that its refractive index is larger than that of the substrate and smaller than that of the active layer on an n-type InP substrate 1 on which striped grooves are formed. After flattening the substrate surface outside the groove area and further forming an InGaAsP active layer 3, a p-type InP cladding layer 4, and an n-type InP layer 5 on the guide layer, the n-type InP layer 5 is formed only on the upper part of the groove area. Removed by etching, then p-type InP type
It had a structure in which an InP layer 6 and a p-type InGaAsP cap layer 7 were formed.

In the above device, the P-type InGaAsP cap layer 7
The current injected into the p-type InP layer 6, the p-type InP cladding layer 4, the InGaAsP active layer 3, and the n-type
The current flows through the InGaAsP guide layer 2 into the n-type InP substrate 1, and the n-type InP layer 5 plays the role of current confinement. In addition, since the n-type InGaAsP guide layer 2 is thicker at the part of the upper part of the groove that is in contact with the active layer light emitting region than the part of the n-type InGaAsP guide layer 2 that is in contact with the active layer non-emissive region at the upper part outside the trench, the n-type InGaAsP guide layer 2 is The equivalent refractive index of the light-emitting region is higher than that of the non-light-emitting region, thereby enabling fundamental transverse mode oscillation.

However, the above device requires two crystal growth steps in its fabrication, that is, in the first crystal growth, the n-type InGaAsP guide layer 2,
InGaAsP active layer 3, p-type InP cladding layer 4, n-type
An InP layer 5 was formed, and in the second growth, a p-type InP layer 6 and a p-type InGaAsP cap layer 7 were formed. The need for two crystal growths means that
This is due to the fact that an etching process is required to provide a current path in a layer formed for the purpose of current confinement, such as n-type InP5 shown in FIG. As a result of the above, the conventional device required many manufacturing steps, which was a drawback of the conventional device.

For this reason, an element with a structure that has characteristics equivalent to those of conventional elements and can be manufactured with fewer manufacturing steps, that is, a current blocking layer formed for the purpose of current confinement, such as the n-type InP layer 5 shown in FIG. There was a need to realize an element with a structure that does not require an etching process to provide a current path even when a current path is formed.

The purpose of the present invention is to improve the drawbacks of conventional elements, to provide an element having characteristics equivalent to those of conventional elements, and having a structure that can be manufactured in fewer manufacturing steps than conventional elements, that is, it can be manufactured by one crystal growth. The goal is to realize an element with a unique structure.

According to the present invention, a cladding having a conductivity type opposite to that of the semiconductor substrate is formed in the groove and on the surface of the substrate outside the groove so that a part of the side surface of the striped groove formed in the semiconductor substrate remains exposed in a striped manner. A layer is formed, and a cladding layer is formed, which has the same conductivity type as the semiconductor substrate, is smaller than the active layer, and is in contact with the exposed side surface of the groove of the semiconductor substrate remaining, and so that the entire surface of the substrate is flat. a guide layer with a larger refractive index is formed in and outside the groove;
Furthermore, the object of the present invention can be achieved by forming an active layer, a cladding layer, and a cap layer sequentially over the entire surface of the substrate.

The present invention will be explained below with reference to the drawings.

Figure 2 shows InP using the n-type substrate of the present invention.
An example of an InGaAsP laser is shown. In Figure 2, n
A part of the groove formed in the InP type substrate 1 on the inside of the substrate, and a part of the side surface of the groove on the substrate surface side where the p-type InP cladding layer 5 is formed on the substrate outside the groove area. has not been in contact with. Then, on the groove side surface that is not in contact with the p-type InP cladding layer 5, there is an n-type
The InGaAsP guide layer 2 is in contact with the guide layer 2, and the guide layer 2 is formed so that the surface of the guide layer above the groove and above the outside of the groove area is flat, and
InGaAsP active layer 3, p-type InP cladding layer 4 and p
A type InGaAsP cap layer 7 is successively formed. Therefore, in the above element, p-type
The current injected into the InGaAsP cap layer 7 is p-type.
InP cladding layer 4, InGaAsP active layer 3, n-type
It flows through the InGaAsP guide layer 2 and into the n-type InP substrate 1 from the portion of the groove side surface of the n-type InP substrate 1 that is in contact with the n-type InGaAsP guide layer 2 . A portion of the InGaAsP active layer 3 above the groove region becomes a light emitting region.

In addition, the n-type InGaAsP guide layer 2 has a refractive index smaller than that of the InGaAsP active layer 3, and
The composition is selected so that the refractive index is higher than that of the cladding layer 5, and the guide layer 2 is formed so that the groove region and the surface of the guide layer above the groove region are flat. The layer thickness is thicker in the groove region than outside the groove region. From this, the equivalent refractive index of the InGaAsP active layer 4 is larger above the groove region than above the outside of the trench region.
This enables stable fundamental transverse mode oscillation.

As described above, the device of the present invention has a structure in which the current flowing outside the light emitting region of the active layer can be reduced by providing a current blocking layer, and stable fundamental transverse mode oscillation is possible, as in the conventional device. It's summery.

On the other hand, even if the p-type InP cladding layer 5 as shown in FIG. Unlike conventional devices, there is no need to form a current blocking layer and then etch a portion of the current blocking layer to create a path for current flow. From this, the device of the present invention can be fabricated by only one crystal growth, whereas conventional devices require two crystal growths due to current blocking layer etching, and the structure of the present invention The device can be manufactured with fewer manufacturing steps than conventional devices.

The embodiment of the present invention uses an n-type substrate shown in FIG.
This is an example of an InP-InGaAsP laser, in which a p-type
An InP cladding layer 5 is formed to a depth of 1.5 μm in the groove region and a thickness of 1 μm outside the trench region, and is further formed using n-type InGaAsP so as to have a thickness of 0.6 μm outside the trench region.
A guide layer 2 is formed so that its surface is flat, and is further covered with an InGaAsP active layer 3 with a thickness of 0.2 μm, a p-type InP cladding layer 4 with a thickness of 2 μm, and an n-type InGaAsP cap layer 7 with a thickness of 1 μm. This is the structure formed.

The above device has characteristics similar to those of conventional current confinement plano-convex lasers, but can be manufactured with fewer manufacturing steps than conventional devices.

As described above, the present invention is an InP-
Although an InGaAsP laser has been described, a p-type substrate may also be used.

Similar effects can also be obtained with GaAs--GaAlAs lasers. For example, using a p-type substrate
In the case of a GaAlAs laser, each symbol in FIG. 2 is as follows. 1 is p-type GaAs substrate, 2 is p-type
GaAlAs guide layer, 3 is GaAlAs active layer, 4 is n
5 is an n-type GaAlAs clad layer, and 7 is an n-type GaAlAs cap layer.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional current confinement plano-convex laser. FIG. 2 is a cross-sectional view of the laser of the present invention. In each figure, 1 is a semiconductor substrate, 2 is a guide layer, 3 is an active layer, 4 is a cladding layer, 5 is a cladding layer for the purpose of blocking current, 6 is a cladding layer, and 7 is a cap layer.

Claims (1)

[Claims] 1. Forming a striped groove in a semiconductor substrate, and forming a first groove having a conductivity type opposite to that of the semiconductor substrate in the groove and on the surface of the substrate outside the groove so that a part of the side surface of the groove remains exposed. forming the first cladding layer, which has the same conductivity type as the semiconductor substrate and has the same conductivity type as the semiconductor substrate, so as to be in contact with the exposed remaining groove side surface and to have a flat surface over the entire surface; a step of forming a guide layer having a refractive index greater than the refractive index of the layer in the groove region and outside the groove region; and a step of forming an active layer having a refractive index greater than the refractive index of the guide layer on the guide layer. and forming a second cladding layer on the active layer that has the same conductivity type as the guide layer and has a refractive index smaller than the refractive index of the active layer. A method for manufacturing a semiconductor laser, characterized in that the guide layer in contact with the light emitting region of the active layer is formed to be thicker than the portion in contact with the outside of the light emitting region so that the equivalent refractive index is larger than that outside the light emitting region. .