JPH07249825A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a semiconductor laser whose threshold current is low and which has an inverted SAG structure. CONSTITUTION:An n-AlGaInP clad layer 2, a GaInP active layer 3, a p-AlGaInP clad layer 4, a p-GaInP etching-stopper layer 5 and a p-AlGaInP clad layer 6 are formed sequentially on an n-GaAs substrate 1 by an MOVPE method. Then, a mesa 22 is formed in a mesa formation process by using a photolithographic technique and an etching technique. After that, a first current-blocking n-layer 30 and a second current-blocking p-layer 31 are formed by an MOVPE method. In addition, an n-electrode 10 and a p-electrode 9 are formed, and this assembly is separated into individual chips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser structure, and more particularly to a semiconductor laser structure having a low operating current.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers have been widely used in information equipment, optical communication and the like. In particular, the AlGaInP semiconductor laser is characterized in that it has an oscillation wavelength as short as 600 to 700 nm and is in the visible range. Taking advantage of this feature,
It is expected to be applied as a light source for pointers, bar code readers, etc., and some have been put to practical use.

FIG. 4 is a structural diagram of a semiconductor laser having an inverted SAS structure. In this figure, 1 is an n-GaAs substrate, 2 is an n-AlGaInP clad layer, 3 is a GaInP active layer, 4 is a p-AlGaInP clad layer, and 5 is p-Ga.
InP etching stopper layer, 6 is p-AlGaInP
Clad layer, 7 is n-GaAs current blocking layer, 8 is p
-GaAs cap layer, 9 is a p-electrode, 10 is an n-electrode, 2
3 is a p-cladding layer n-type inversion region, and 40, 41 and 42 are current paths.

The operation will now be described. p electrode 9,
When a voltage is applied to the n-electrode 10 in the forward bias direction, a current flows along the current path 40, and radiative recombination of injected carriers occurs in the active layer 3 to emit laser light. Here, since the conductivity type of the current block layer 7 is n-type, the conductivity type of the current path 41 passing through the current block layer is n-pn, and almost no current flows along this path. On the other hand, the conductivity type of the current path 40 that does not pass through the current block layer 7 is pn, and a current easily flows in the forward bias state. That is, the n-current blocking layer 7 functions to efficiently collect the injected current in the current path 40, and realizes the low current operation of the semiconductor laser.

Next, the manufacturing method will be described. First, n-Al is formed on the substrate 1 by, for example, the MOVPE method.
GaInP clad layer 2, GaInP active layer 3, p-A
The 1GaInP clad layer 4, the p-GaInP etching stopper layer 5, and the p-clad layer 6 are sequentially formed. Next, the side of the mesa is selectively etched right above the etching stopper layer 5 to form the mesa 22. Then, n-
GaAs current blocking layer 7, p-GaAs cap layer 8
To form. Further, an n-electrode 10 and a p-electrode 9 are formed and separated into chips.

[0006]

However, if a pinhole is formed in a portion of the etching stopper layer for some reason such as the presence of hillocks in the mesa forming step in the manufacturing process, the p-clad under the pinhole is formed. Layer 4 is easily etched. In the subsequent formation of the n-current blocking layer, a p-clad n-type inversion region 23 is formed in the etched region. At this time, from the p electrode 9 to the p-clad n inversion region 23
The conductivity type of the current path 42 reaching the n-electrode 10 through the n-type becomes n-type and exhibits the same behavior as a normal ohmic resistance.
This becomes a current short circuit path, a reactive current flows, and low threshold operation of the semiconductor laser becomes difficult.

[0007]

In order to solve the above-mentioned problems, the structure of the semiconductor laser of the present invention includes a region of a conductivity type opposite to that of the substrate in a part of the conductivity type of the current blocking layer.

[0008]

According to the present invention, since the current blocking layer includes a region having a conductivity type opposite to the conductivity type of the substrate, even if the conductivity type inversion region exists in the clad layer below the current blocking layer, the semiconductor does not exist. A low current operation of the laser is realized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. FIG. 1A is a sectional view for explaining the first embodiment of the structure of the semiconductor laser of the present invention, and FIG. 1B is an enlarged view of a main part of FIG. 1A. In this figure, FIG.
Those having the same reference numerals as those in FIG.
As first current blocking layer, 31 is a p-GaAs second current blocking layer, and 43 and 44 are current paths.

First, the manufacturing method will be described. Figure 1
As shown in (a), the n-AlGaInP cladding layer 2, the GaInP active layer 3, the p-AlGaInP cladding layer 4, and the p-GaInP are formed on the substrate 1 by the MOVPE method.
The etching stopper layer 5 and the p-AlGaInP cladding layer 6 are sequentially formed. Next, photolithography technology,
Then, the mesa 22 is formed by a mesa formation process using an etching technique. After that, the n-first current blocking layer 30 and the p-second current blocking layer 31 are formed by the MOVPE method. Further, an n-electrode 10 and a p-electrode 9 are formed and separated into chips.

Next, the operation will be described. The basic operation is similar to that of a conventional laser. However, in the laser of the present invention, the current path 43 corresponding to the current path 42 of the conventional example is used.
Has a pn junction, and leakage current is reduced as compared with a single conduction type ohmic resistance. The current path 44
There is also a single n-type current path as shown in, but this path is extremely thin and the leakage current is small.

Next, a second embodiment will be described with reference to FIG. 2A is a sectional view for explaining a second embodiment of the structure of the semiconductor laser of the present invention, and FIG. 2B is FIG.
It is a principal part enlarged view of (a). In this figure, the same reference numerals as those in FIG. 1 denote the same elements, and 32 denotes n-GaAs.
The third current blocking layers 45 and 46 are all current paths.

The basic manufacturing method is the same as that of the first embodiment. The difference from Example 1 is that n-GaA in Example 1 is different.
After forming the s first current blocking layer 30 and the p-GaAs second current blocking layer 31, the n-GaAs third current blocking layer 32 is further formed. In the case of the present embodiment, since the conductivity type of the current path 45 corresponding to the current path 43 in the first embodiment is npn, the leakage current can be further reduced compared to the pn type current path. The current path 4
There is also a pn type current path as shown in 6, but this path is extremely thin and the leakage current is small.

Next, a third embodiment will be described with reference to FIG. 3A is a sectional view for explaining a third embodiment of the structure of the semiconductor laser of the present invention, and FIG. 3B is FIG.
It is a principal part enlarged view of (a). In this figure, the same symbols as those in FIG. 1 indicate the same components, 8 is a p-GaAs cap layer, and 47 is a current path.

The basic manufacturing method is the same as that of the first embodiment. The difference from Example 1 is that n-GaA in Example 1 is different.
s After forming the first current blocking layer 30 and the p-GaAs second current blocking layer, a p-GaAs cap layer is further formed. In the case of the present embodiment, the conductivity type of the current path 47 corresponding to the current path 44 in the first embodiment is pn.
Therefore, the leakage current can be further reduced as compared with the single n-type path.

In addition to the above embodiments, there are various methods of reducing the leakage current by controlling the conductivity type of the block layer, for example, by combining the embodiments 2 and 3, and the threshold current Of course, the reduction of

The same effect can be obtained with a laser using a quantum well active layer, a multiple quantum barrier, and a laser made of a material other than AlGaInP.

Further, although the case of the laser formed on the n-type substrate has been described above, it is clear that the same effect can be obtained in the case of the laser formed on the p-type substrate by reversing the conductivity types. is there.

[0019]

As described above, since the structure of the semiconductor laser of the present invention includes a region of the conductivity type of the current block layer which is opposite to the conductivity type of the substrate, the leakage current passing through the current block layer is prevented. It was possible to reduce.

[Brief description of drawings]

FIG. 1A is a sectional view of a semiconductor laser for explaining a first embodiment of the present invention, and FIG. 1B is an enlarged view of a main part of FIG.

FIG. 2A is a sectional view of a semiconductor laser for explaining a second embodiment of the present invention, and FIG. 2B is an enlarged view of a main part of FIG.

FIG. 3A is a sectional view of a semiconductor laser for explaining a third embodiment of the present invention, and FIG. 3B is an enlarged view of a main part of FIG.

FIG. 4 is a sectional view of a semiconductor laser for explaining a conventional example.

[Explanation of symbols]

 1 n-GaAs substrate 2 n-AlGaInP clad layer 3 GaInP active layer 4 p-AlGaInP clad layer 5 p-GaInP etching stopper layer 6 p-AlGaInP clad layer 7 n-GaAs current blocking layer 8 p-GaAs cap layer 9 p electrode 10 n electrode 22 mesa 23 p clad layer n-type inversion region 30 n-GaAs first current block layer 31 p-GaAs second current block layer 32 p-GaAs third current block layer 40 current path 41 current path 42 current path 43 Current path 44 Current path 45 Current path 46 Current path 47 Current path

Claims (1)

[Claims] 1. A semiconductor laser having a mesa structure formed in a clad layer on an upper surface of an active layer and a block layer formed on both sides of the mesa structure due to current confinement, wherein the conductivity type of the current block layer is one. A semiconductor laser, characterized in that the portion includes a region having a conductivity type opposite to that of the substrate.