JPH0645702A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser, provided with a refractive index waveguide structure, which can be manufactured by a single process. CONSTITUTION:In the semiconductor laser in which an active layer 3 is pinched by the upper and lower two clads layers 2 and 4 which are formed in a semiconductor layer substrate, the ions which make a grating constant a little larger than the clad layer 2 are implanted into the part corresponding to the center part of the active layer 3 of the clad layer 2, an active layer 3 is grown on the upper surface of the clad layer 2, and a refractive index waveguide structure is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser capable of obtaining a refractive index waveguide structure without etching an active layer.

[0002]

2. Description of the Related Art In a semiconductor laser, in order to confine optical power in a region as narrow as possible to increase the stimulated emission rate and create conditions advantageous for laser oscillation, in order to create an advantageous condition for laser oscillation, an elongated stripe-shaped embedding is formed in the center of the active layer for confining the excitation current of the laser. An active layer is built in.

By the way, conventionally, for this reason, a semiconductor having a smaller forbidden band width and a larger refractive index than the active layer is embedded in the central portion of the active layer. The layer was removed by etching, leaving a striped width of several μm in the center, and pnp was formed on the removed portion.
A current blocking layer having an n thyristor structure (or pnp, npn) is formed to obtain a buried active layer.

However, the width of the central striped portion (embedded active layer) of the active layer remaining after etching is
Since it is as small as several μm, it is not easy to control the width and perform etching.

[0005]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a semiconductor laser provided with a refractive index waveguide structure which can be easily manufactured.

[0006]

A semiconductor laser according to the present invention, which is proposed to achieve the above object, has an active layer composed of two upper and lower clad layers formed in a semiconductor laminated substrate. In the sandwiched semiconductor laser, after forming the lower clad layer, ions that make the lattice constant slightly larger than that of the clad layer are injected into the part corresponding to the central part of the active layer of the clad layer, and the upper surface of this clad layer is injected. An active layer is formed on the substrate to form a refractive index guiding structure.

A semiconductor laser according to a second aspect of the present invention is a semiconductor laser in which an active layer is sandwiched between two upper and lower clad layers formed in a semiconductor laminated substrate, and after the active layer is formed, the center of the active layer is formed. Ions are implanted into the portion to make the band gap smaller than that of the active layer, so that a refractive index guiding structure is formed.

[0008]

In the semiconductor laser according to the present invention as set forth in claim 1, after the formation of the lower clad layer, the portion of the clad layer corresponding to the lower part of the central portion of the active layer has a lattice constant slightly higher than that of the clad layer. Since the active layer is formed on the upper surface of this clad layer after implanting ions to increase the size, the stripe-shaped part in the center of the active layer is affected by the part of the lower clad layer that has a slightly larger lattice constant and is stretched. Distortion occurs, the forbidden band width is small, the refractive index is large, and a refractive index waveguide structure can be formed.

In the semiconductor laser according to the present invention as set forth in claim 2, after the active layer is formed, ions for making the band gap smaller than that of the active layer are implanted into the central portion of the active layer. In the central portion of, the forbidden band width is small, the refractive index is large, and a refractive index waveguide structure can be formed.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the structure of an AlGaAs semiconductor laser from the front as an example of the semiconductor laser according to the first aspect of the present invention, and shows an example in which a double hetero structure is formed. On the upper surface of the n-GaAs substrate 1, a clad layer composed of an n-AlGaAs layer 2 and a p-AlGaAs layer 4 is sandwiched from above and below,
An active layer 3 made of a GaAs layer is formed, and a cap layer 5 made of a p-GaAs layer is formed on the active layer 3, and a portion of the clad layer corresponding to a lower portion of the stripe-shaped portion C at the center of the active layer 3. The lattice constant of B is made slightly larger, and the stripe-shaped portion C in the center of the active layer 3 immediately above is shown.
Has a structure in which a refractive index waveguide structure having a smaller forbidden band width and a larger refractive index than the other portions of the active layer 3 is formed.

The semiconductor laser having such a structure is formed by the following method. On the upper surface of the n-GaAs substrate 1,
After forming the n-AlGaAs cladding layer 2, as shown in FIG. 2, In ions A are implanted into the portion B of the cladding layer corresponding to the lower portion of the stripe-shaped portion C in the center of the active layer 3. As a result, the lattice constant of the portion B of the clad layer into which the In ions A are implanted is slightly large (In has a large molecular weight and therefore has a large number of atoms. Therefore, the larger the composition ratio of the semiconductor, the lattice of the semiconductor. The constant will also increase). FIG. 3 is a view of the n-AlGaAs cladding layer 2 seen from above.

Next, after the annealing process (heat treatment) is performed to adjust the lattice structure, the GaAS active layer 3 is formed.
Since the thickness of the As active layer 3 is thin, the C portion of the GaAs active layer 3 on the portion B where the In ions A are implanted is subjected to tensile strain due to the influence of the lattice constants of the underlying cladding layers 2 and B. . Here, FIG. 4 (a) shows that when it is subjected to compressive strain, (b)
Is the natural state, (c) is the forbidden band width E when subjected to tensile strain
It represents the change of g. When tensile strain is applied,
As shown in (c), the forbidden band width Eg is smaller than that in the natural state of (b). Further, the refractive index of the III-V mixed crystal semiconductor tends to increase as the forbidden band width Eg decreases.

Therefore, the GaAs active layer 3 which is subjected to tensile strain
In part C, the forbidden band width Eg becomes small and the refractive index becomes large. Therefore, the active layer 3 has a distribution in which the forbidden band width Eg is large-small-large and the refractive index is small-large-small in the lateral direction, and a refractive index waveguide structure is formed. Next, after p-AlGaAs cladding layer 4 and p-GaAs cap layer 5 are formed in this order, p-electrode 6 and n-electrode 7 are added to obtain a semiconductor laser having a refractive index waveguide structure.

In the above embodiment, the AlGaAs semiconductor laser has been described, but other semiconductor lasers such as AlGaInP semiconductor laser can be similarly implemented. FIG. 5 shows, as an example of the semiconductor laser according to the second aspect of the present invention, the structure of an AlGaInP-based semiconductor laser from the front side, and shows an example in which the structure is a double hetero type. An active layer 10 formed of a GaInP layer is formed on the upper surface of the n-GaAs substrate 8 so as to be sandwiched by a clad layer composed of an n-AlGaInP layer 9 and a p-AlGaInP layer 11 from above and below, and p is formed thereon. —Cap layer 12 made of GaInP layer
In the stripe-shaped portion E at the center of the AlGaInP active layer 10, the composition ratio of Ga is slightly large, the forbidden band width is smaller than the other portions of the active layer 10, and the refractive index guiding structure is large. Is formed.

The semiconductor laser having such a structure is formed by the following method. On the upper surface of the n-GaAs substrate 8,
After forming the n-AlGaInP clad layer 9 and the AlGaInP active layer 10, as shown in FIG.
Ga ions D are implanted in the central stripe portion E of the P active layer 10. FIG. 7 is a view of the AlGaInP active layer 10 viewed from above.

Here, Ga is formed in the AlGaInP active layer 10.
When the amount of ion D is small, it is sufficiently incorporated into the lattice structure when the amount is small, and the Ga composition ratio becomes larger than the Al composition ratio. From the relationship between the composition ratio of Ga and Al and the forbidden band width, it is known that the forbidden band width becomes smaller as the Ga composition ratio becomes larger than the Al composition ratio. Further, the refractive index of the III-V group mixed crystal semiconductor tends to increase as the forbidden band width decreases.

Therefore, Al implanted with Ga ions D
The stripe-shaped portion E at the center of the GaInP active layer 10 is
The forbidden band becomes smaller and the refractive index becomes larger. Therefore,
The active layer 10 has a distribution in which the forbidden band width is large-small-large and the refractive index is small-large-small in the lateral direction, and a refractive index waveguide structure is formed. Then, after annealing (heat treatment) to adjust the lattice structure, the p-AlGaInP cladding layer 11 and the p-G are formed.
The aInP cap layer 12 is formed in this order, a p-electrode 13 and an n-electrode 14 are added, and a semiconductor laser having a refractive index waveguide structure is obtained.

[0018]

According to the semiconductor laser of the present invention as set forth in claim 1, after the lower clad layer is formed, a portion of the clad layer corresponding to a lower part of the central portion of the active layer is formed more than the clad layer. After implanting ions that make the lattice constant a little larger, the active layer is formed on the upper surface of this clad layer. It is affected by the tensile strain, the forbidden band width is small, the refractive index is large, and the refractive index waveguide structure can be formed. Therefore, the refractive index waveguide structure can be provided without going through the etching process of the active layer, which is difficult to control.

According to another aspect of the semiconductor laser of the present invention, after the active layer is formed, the central portion of the active layer is
Since the ions for making the forbidden band width smaller than that of the active layer are implanted, the forbidden band width is small and the refractive index is large in the central portion of the active layer, so that a refractive index waveguide structure can be formed. Therefore,
Without going through the etching process of the active layer, which is difficult to control,
A refractive index guiding structure can be provided.

[Brief description of drawings]

FIG. 1 is a structural diagram showing from the front an embodiment of a semiconductor laser according to the present invention according to claim 1.

FIG. 2 is a diagram for explaining a manufacturing process of the semiconductor laser according to the present invention as set forth in claim 1;

FIG. 3 is a view of the n-AlGaAs cladding layer viewed from above.

FIG. 4A is a diagram showing a change in the forbidden band width Eg when subjected to compressive strain. (B) is a diagram showing a forbidden band width Eg in a natural state. (C) is a diagram showing a change in the forbidden band width Eg when subjected to tensile strain.

FIG. 5 is a structural diagram showing from the front an embodiment of the semiconductor laser according to the present invention as defined in claim 2;

FIG. 6 is a drawing for explaining the manufacturing process of the semiconductor laser according to the present invention as defined in claim 2;

FIG. 7 is a view of the AlGaInP active layer viewed from above.

[Explanation of symbols]

2 ... n-AlGaAs clad layer 3 ... GaAs active layer 4 ... p-AlGaAs clad layer 9 ... n-AlGaInP clad layer 10 ... AlGaInP active layer 11 ... p-AlGaInP clad layer B ... A portion of the n-AlGaAs cladding layer corresponding to the lower part of the central striped portion of the GaAs active layer C ... Central striped portion of the GaAs active layer E ... Central striped portion of the AlGaInP active layer part

Claims (2)

[Claims] 1. A semiconductor laser in which an active layer is sandwiched between two upper and lower clad layers formed in a semiconductor laminated substrate, and a portion of the clad layer corresponding to a central portion of the active layer after the lower clad layer is formed. A semiconductor laser having a refractive index guiding structure in which an ion having a lattice constant slightly larger than that of the clad layer is implanted, and an active layer is formed on the upper surface of the clad layer. 2. A semiconductor laser in which an active layer is sandwiched between two upper and lower clad layers formed in a semiconductor laminated substrate, and after the formation of the active layer, a forbidden band width is provided in the central portion of the active layer as compared with the active layer. A semiconductor laser characterized in that a refractive index guiding structure is formed by implanting ions for reducing the size.