JPH0482074B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In a buried semiconductor laser in which both sides of a band-shaped mesa including a light-emitting portion of a double heterostructure are buried regions, a current blocking layer on the substrate side that constitutes the buried region is By creating a two-layer structure from the substrate side, consisting of a region with high impurity concentration and a region with low impurity concentration.

The current blocking performance of the buried region is improved to obtain high laser light output.

[Industrial application field]

The present invention relates to a buried semiconductor laser, and in particular,
Regarding the configuration of the embedded area.

Semiconductor lasers have come to be frequently used as optical signal sources in optical communications and information processing that use light as a medium to handle large amounts of information.

Semiconductor lasers used in this way include buried semiconductor lasers, such as BH lasers (Buried
Heterostructure Laser), but further improvements in characteristics such as increased optical output are desired.

[Conventional technology]

FIG. 3 is a side sectional view of a BH laser which is a typical example of a conventional buried semiconductor laser.

In the same figure, 1 is n-type indium phosphide (InP)
2 is an n-type InP cladding layer, 3 is an indium gallium arsenide phosphide (InGaAsP) active layer, and 4 is an n-type InP cladding layer.
5 is a p-type InP cladding layer, 5 is a p-type InGaAsP contact layer, 6 is a band-shaped mesa formed by 2 to 5, and the active layer 3 portion here serves as a light emitting portion having a double heterostructure.

Both sides of the mesa 6 become buried regions 7, and a current blocking layer 8 of p-type InP, a current blocking layer 9 of n-type InP, and a p-type
It is composed of a buried layer 10 of InGaAsP.

Moreover, 11 and 12 are metal electrodes.

In this semiconductor laser, when an applied current is passed between electrodes 11 and 12 with electrode 11 on the positive side, current blocking layers 8 and 9 form a P-N junction in the opposite direction.
Due to the fact that the rising voltage between the current blocking layer 8 and the cladding layer 2 is higher than that between the cladding layers 4 and 2, current is concentrated in the active layer 3 and oscillates to emit laser light.

[Problem that the invention seeks to solve]

The rising voltage between the current blocking layer 8 and the cladding layer 2 is due to the leakage current a that passes through the junction between the cladding layer 4 and the current blocking layer 8 and becomes ineffective against oscillation.
The higher the value, the better.

In order to increase this rising voltage, it is effective to increase the impurity concentration of the current blocking layer 8.

However, if the impurity concentration is too high, the resistance of the current blocking layer 8 will decrease and the leakage current a will increase, so when focusing on the leakage current a, there is a limit to the height of the impurity concentration. , the rise voltage cannot be made high enough.

On the other hand, when the impurity concentration is lowered to increase the resistance of the current blocking layer 8, the rising voltage is reduced and at the same time, the cladding layer 4 or the buried layer 10, the current blocking layer 9, the current blocking layer 8, and the cladding layer 2 are formed. The P-N-P-N structure operates as a thyristor, generates an extremely large leakage current b, and loses its function as a laser.

In the semiconductor laser formed under these constraints, when the applied current is increased to increase the optical output, the leakage current a increases more than the rate of increase of the applied current due to the accompanying increase in the potential of the cladding layer 4. However, as shown in A of the optical output-applied current characteristic diagram in FIG. 2, there is a problem in that the rate of increase in optical output decreases when the applied current is large, making it difficult to obtain a large optical output.

[Means for solving problems]

FIG. 1 is a side sectional view of an embodiment of a buried semiconductor laser according to the present invention.

The above problem is that, as shown in FIG. 1, the buried regions 7 disposed on both sides of the strip-shaped mesa 6 including the double heterostructure light emitting portion and formed on the semiconductor substrate 1 of one conductivity type are on the substrate 1
First reverse conductivity type semiconductor layer 8a forming a pn junction
, a second reverse conductivity type semiconductor layer 8b which is on the first reverse conductivity type semiconductor layer 8a and has a lower impurity concentration than the first reverse conductivity type semiconductor layer 8a; and the second reverse conductivity type semiconductor layer 8a. A semiconductor layer 9 of one conductivity type is formed on the layer 8b and forms a pn junction with the second opposite conductivity type semiconductor layer 8b, and an interface between the strip mesa 6 and the buried region 7 is formed. In this case, the upper surface of the second opposite conductivity type semiconductor layer 8b is the active layer 3 of the light emitting section.
The second reverse conductivity type semiconductor layer 8b is located above the upper surface and the lower surface of the second reverse conductivity type semiconductor layer 8b is located below the lower surface of the active layer 3.
The problem is solved by a buried semiconductor laser in which b is disposed.

[Effect]

In the above structure, the current blocking layer 8 shown in FIG. 3 has a two-layer structure of current blocking layers 8a and 8b.

By lowering the impurity concentration of the current blocking layer 8b, it is possible to make the resistance sufficiently high against the current flowing in from the mesa 6 (leakage current a shown in FIG. 3).

Accordingly, the impurity concentration of the current blocking layer 8a can be increased without worrying about low resistance, and the rising voltage between the current blocking layer 8a and the substrate 1 side can be sufficiently increased.

Further, even if the impurity concentration of the current blocking layer 8b is low, the impurity concentration of the current blocking layer 8a is high, so that the diffusion length of carriers entering from the substrate 1 side is shortened, and the occurrence of the above-mentioned thyristor operation is suppressed.

For these reasons, in the present semiconductor laser, the current blocking performance of the buried region is improved, and even if the applied current is increased, the rate of increase in optical output does not decrease, making it possible to obtain high optical output.

〔Example〕

An example will be described below with reference to FIG.

The semiconductor laser shown in FIG.
and 8b have been replaced with a two-layer structure, and the rest remains unchanged.

That is, the current blocking layer 8a has an impurity concentration of 4×
10 ¹⁸ /cm ³ p-type InP, and the current blocking layer 8b
is p-type InP with an impurity concentration of 2×10 ¹⁵ /cm ³ . Incidentally, the impurity concentration of the conventional current blocking layer 8 is 5×10 ¹⁷ /cm ³ . Cadmium (Cd) or zinc (Zn) is used as an impurity in each case.

Further, the impurity concentration of the n-type InP current blocking layer 9 is 5×10 ¹⁷ /cm ³ , and tin (Sn) is used as the impurity.

The optical output-applied current characteristics of the semiconductor laser formed as described above corresponding to the conventional example shown in FIG. 3 are as follows:
As shown in B of FIG.

When compared with characteristic A of the conventional example shown in the same figure,
In characteristic A, the rate of increase in optical output decreases when the optical output exceeds 10 mW, and the decrease becomes larger as the applied current increases, whereas in characteristic B, the rate of increase remains almost constant even when the optical output reaches 40 mW. This shows that the optical output of this semiconductor laser is much higher than that of the conventional one.

Note that in this example, since the liquid phase growth method was used to form the current blocking layers 8a, 8b, etc., the current blocking layers 8a, 8b, etc.
The impurity concentration of b can be reduced to 2×10 ¹⁵ /cm ³ as described above, but if it can be further reduced (e.g., to about 10 ¹¹ /cm ³ ) by, for example, vapor phase growth, the present invention can be applied. The configuration becomes more effective.

Furthermore, the configuration of the present invention is also effective when applied to other buried semiconductor lasers, such as PBH lasers, which differ from the embodiments in terms of their operation.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention,
In a buried semiconductor laser where both sides of a band-shaped mesa including a double heterostructure light emitting part are buried regions,
The current blocking performance of the buried region is improved and a high laser light output can be obtained, which has the effect of making it possible to provide a semiconductor laser that is excellent as an optical signal source.

[Brief explanation of drawings]

FIG. 1 is a side cross-sectional view of an embodiment of a buried semiconductor laser according to the present invention, FIG. 2 is an optical output-applied current characteristic diagram of an embodiment of the present invention and a conventional example, and FIG. 3 is a diagram of a conventional buried semiconductor laser. FIG. 2 is a side sectional view of a typical example of a laser. In the figure, 1 is a substrate (one conductivity type semiconductor substrate);
2 and 4 are cladding layers, 3 is an active layer, 5 is a contact layer, 6 is a mesa, 7 is a buried region, 8 is a current blocking layer, 8a is a current blocking layer (first reverse conductivity type semiconductor layer), 8b 9 is a current blocking layer (second opposite conductivity type semiconductor layer); 9 is a current blocking layer (one conductivity type semiconductor layer); 10 is a current blocking layer (second opposite conductivity type semiconductor layer);
is a buried layer, 11 and 12 are electrodes, a and b are leakage currents, A is a characteristic of the conventional example, and B is a characteristic of the embodiment.

Claims (1)

[Scope of Claims] 1. A buried region 7, which includes a double heterostructure light emitting portion and is disposed on both sides of a strip-shaped mesa 6 formed on a semiconductor substrate 1 of one conductivity type, is located on the substrate 1 and A first opposite conductivity type semiconductor layer 8a forming a pn junction with the substrate 1, and a second opposite conductivity type semiconductor layer 8a which is on the first opposite conductivity type semiconductor layer 8a and has a lower impurity concentration than the first opposite conductivity type semiconductor layer 8a. a second opposite conductivity type semiconductor layer 8b and one conductivity type semiconductor layer 9 which is on the second opposite conductivity type semiconductor layer 8b and forms a pn junction with the second opposite conductivity type semiconductor layer 8b. At the interface between the band-shaped mesa 6 and the buried region 7,
The upper surface of the second reverse conductivity type semiconductor layer 8b is located above the upper surface of the active layer 3 of the light emitting section, and the lower surface of the second reverse conductivity type semiconductor layer 8b is located below the lower surface of the active layer 3. A buried semiconductor laser characterized in that the second opposite conductivity type semiconductor layer 8b is disposed so as to be located at .