JPS622715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the lifetime characteristics of a semiconductor laser device, and particularly to a semiconductor laser device having a double heterostructure made of a mixed crystal containing Ga, Al, and As.

G _a1-x Al _x As light-emitting devices with an emission wavelength of 8000 Å have made rapid progress in recent years, and semiconductor lasers in particular have been reported to have an estimated lifetime of 10 ⁵ to ^{10 6} hours at room temperature, making them ideal for optical communications. light source. In order to achieve a longer lifetime for this light emitting device, it is possible to reduce the defect density in the grown crystal by improving crystal growth technology and reducing oxygen in the growth system, thereby suppressing the occurrence of dark lines and dark spots. The major success factors were the ability to protect the reflective end face with a dielectric film to prevent end face corrosion.

A double heterostructure G _a1-x Al _x As semiconductor laser device with an oscillation wavelength in the 8000 Å band has a cladding layer.
Since the Al mixed crystal ratio can be kept below 0.4, n
Si, which has a relatively small segregation coefficient, is used as an impurity in the mold.
Impurities such as Sn can be used. However, as the Al mixed crystal ratio x of G _a1-x Al _x As increases, the segregation coefficient decreases and the ionization energy increases. is difficult to obtain. Therefore, when the oscillation wavelength is in the 7000 Å band and the Al mixed crystal ratio of the cladding layer is 0.4 or more, Se, which has a large segregation coefficient as an n-type impurity, is
(Selenium) can be used. Although this Se has a large segregation coefficient and has the effect of increasing the carrier concentration, it is not suitable for obtaining good crystallinity. That is, when a large amount of Se is added, it is difficult to obtain a crystal with good flatness, and when the carrier concentration is 5×10 ¹⁸ cm ^-3 or more, the surface of the grown crystal takes on a terraced morphology. Further, even if the amount added is less than that, a wavy shape is often exhibited when the carrier concentration is 1×10 ¹⁷ cm ⁻³ or more.

As described above, it is extremely difficult to obtain a laser device that has a cladding layer with a desirable carrier concentration of 1×10 ¹⁷ cm ^{-3 or} more as a cladding layer of a semiconductor laser device and is made of a crystal with good flatness. It was hot.

Furthermore, when an active layer is grown on an n-type cladding layer to which Se has been added, the flatness of the active layer also deteriorates, resulting in an increase in scattering loss. The interface between the n-type cladding layer and the active layer, which has a growth pattern of 1.5 mm, contains many defects due to the segregation of Se. These defects have a very large effect on the life characteristics of the semiconductor laser.

An experimental example showing the influence of Se mentioned above will be explained below.

FIG. 1 is a cross-sectional view of a conventional semiconductor laser device used in this experiment. This device consists of an n-type GaAs substrate 2
Above are an n-type Ga0.67Al0.33As cladding layer 3, an Si-doped n-type Ga0.93Al0.07As active layer 4, a Ge-doped p-type Ga0.67Al0.33As cladding layer 5, and a Ge-doped p-type GaAs cap layer. 6 was continuously grown by liquid phase growth, and then CVD (chemical vapor
deposition: vapor phase growth accompanied by chemical reactions)
An oxide film with a double heterostructure in which an Al ₂ O ₃ film 7 is formed, a band-shaped window 9 is formed on the film 7 by photolithography, and a p-type electrode 8 and an n-type electrode 1 are provided at the upper and lower ends, respectively. This is a striped semiconductor laser device. Si is added as an impurity to the n-type cladding layer 3.
We fabricated two types of laser devices doped with Se and Se. The end faces of these elements were covered with an Al ₂ O ₃ film, and the oscillation wavelength was approximately 835 nm at 25°C.

When the above two types of laser devices were driven at 50° C. with an output of 5 mW on one side, the drive current for the laser devices at some initial drive currents showed changes over time as shown in FIG. In Figure 2, the vertical axis represents the drive current, the horizontal axis represents time, and the solid line S
is for the element doped with Si, and the broken line T is for the element doped with Si.
This is the case of a device doped with . From FIG. 2, it was found that the deterioration rate of the element doped with Se was faster.

As can be seen from the above experiments, conventional laser elements can operate stably using Si or Sn when the oscillation wavelength is in the 8000 Å band, but when the oscillation wavelength is in the 7000 Å band, requires the use of Se, which has the disadvantage of shortening the lifespan.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, and to provide a device with excellent life characteristics that can operate stably for a long time.
An object of the present invention is to provide a double heterostructure semiconductor laser device having a Ga _1-x Al _x As-based Se-doped cladding layer.

In order to achieve the above object, the present invention grows a p-type cladding layer or a light guide layer, from which good crystals can be obtained relatively easily, before an active layer, and then grows an active layer on top of the active layer, and then Se on top of the active layer. It is characterized by growing an undoped buffer layer and a Se-doped n-type cladding layer to suppress deterioration caused by defects occurring at the interface between the active layer and the Se-doped n-type cladding layer, thereby achieving a longer life. do.

If the Se-doped n-type cladding layer is grown before the active layer, it is difficult to obtain a well-planar growth layer for the Se-doped cladding layer, resulting in poor planarity of the active layer and increased scattering loss. Become. Furthermore, when an active layer is grown next to a Se-doped n-cladding layer, defects generated at the interface between the n-cladding layer and the active layer will shorten the life of the device. If an active layer is grown on a Se-doped n-type cladding layer and then an Se-free n-type buffer layer, the interface between the Se-doped n-type cladding layer and the n-buffer layer, which contains defects caused by Se, will be in the active layer. Although it has the effect of suppressing deterioration because it does not come into contact with the active layer, the crystallinity of the active layer is inhibited because the active layer is grown after the Se-doped n-type cladding layer, which has poor crystallinity.

In the present invention, first, the p-type cladding layer is grown before the active layer, and the Se-doped n-type cladding layer, which has problems with crystallinity and flatness, is grown after the active layer. Improved crystallinity and flatness. The second is Se after the active layer.
After growing a buffer layer without doping Se
Deterioration is further suppressed by growing a doped n-type cladding layer and separating the Se-doped n-type cladding layer, which contains defects caused by Se, from the active layer, which accelerates deterioration due to recombination of electrons and holes. .
When the conductivity type of the buffer layer grown next to the active layer is n-type, the conductivity type of the active layer can be either n-type or p-type, but when the buffer layer is made p-type, the active layer As a p-type, it is necessary to form a pn junction between the bar layer and the n-type cladding layer.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 3 is a cross-sectional configuration diagram showing an embodiment of the present invention.

N-type GaAs current limiting layer 2 on p-type GaAs substrate 21
After growing 2, ammonia water: hydrogen peroxide water:
A V-shaped groove 27 is formed by photolithography using an etching solution of water = 1:1:50, and a Zn-doped p-type Ga0.45Al0.55As cladding layer 2 is formed thereon.
3. Ge-doped p-type Ga0.87Al0.18As active layer 24,
Si-doped n-type Ga0.87Al0.13As buffer layer 30,
Se-doped n-type Ga0.45Al0.55As cladding layer 25,
After the Se-doped n-type GaAs cap layer 26 is continuously grown by liquid phase growth, the n-type electrode 1 and the p-type electrode 8 are formed by vapor deposition or the like. In this example,
Current confinement is performed by the current limiting layer 22,
Since the active layer 24 and the buffer layer 30 are grown to be thickest at the central portion above the V-shaped groove, an effective refractive index difference is formed in the lateral direction.

In the above configuration, the light within the active layer 24 is effectively guided and collected at the center of the layer due to the refractive index difference, and light leaking into the current limiting layer 22 and being absorbed is suppressed. That is, when the active layer 24 is flat and has no thickness distribution, light spreads laterally,
The current is absorbed into the current limiting layer 22, and as a result, electron-hole pairs are excited within the current limiting layer 22, and the current flows through the layer 22.
However, in this embodiment, a thickness distribution is provided in the active layer 24 to provide an effective refractive index distribution, and the current limiting effect of the current limiting layer 22 is improved. can be fully demonstrated.

Furthermore, if an n-type GaAs current limiting layer 22 is used, n
The diffusion length of holes in type GaAs is 2 μm or less,
Since the thickness is smaller than that of a normally used current limiting layer, electrons injected into the current limiting layer will not penetrate through the layer, and the current can be effectively confined.

When a device according to this embodiment is actually fabricated, the oscillation wavelength will be approximately 760 nm, and the threshold current will be 30~30 nm at 25°C.
It was 50mA. When this element was driven at 70°C and a constant output of 3 mW, the result was 3 × 10 ³ as shown in Figure 4.
There was almost no deterioration in the drive current over a period of time, and this was a significant improvement compared to a device in the same wavelength range in which a conventional Se-doped n-type cladding layer was grown before the active layer.

In the above embodiments, the active layer is grown directly on the p-type cladding layer, but the present invention can of course be applied to cases where a light guide layer is inserted between the active layers. Si is also used as an impurity in the buffer layer.
In addition, in the case of n-type, Sn etc. can be used.
In the case of p-type, Zn, Ge, etc. can be used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram of a conventional oxide film stripe type laser device. FIG. 2 is a characteristic diagram showing the change over time in the drive current of the device shown in FIG. FIG. 3 is a cross-sectional configuration diagram of a laser element showing an embodiment of the present invention. FIG. 4 is a characteristic diagram showing changes over time in the drive current of the laser element shown in FIG. 3. 1, 8...electrode, 21...substrate, 22...current limiting layer, 23, 25...cladding layer, 24...active layer.

Claims (1)

[Claims] 1. In a double heterojunction semiconductor laser device made of a mixed crystal containing at least three elements, Ga, Al, and As, a P-type cladding layer, an active layer, a buffer layer, and an n-type cladding layer are provided. A multilayer crystal layer is formed by sequentially stacking layers, and as an impurity in the n-type cladding layer,
1. A semiconductor laser device characterized in that Se is added and the buffer layer to which Se is not added is interposed between the active layer and the n-type cladding layer. 2. The semiconductor laser device according to claim 1, wherein a p-type optical guide layer is interposed between the p-type cladding layer and the active layer.