JPS6152600B2 - - 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 made of a mixed crystal containing Ga, A, and As.
The present invention relates to a semiconductor laser device having a double heterostructure.

Ga _1-x Al _x As-based light emitting devices, whose emission wavelength is in the 8000 Å band, have made rapid progress in recent years, and semiconductor lasers in particular have been reported to have an estimated lifespan of 10 ⁵ to ^{10 6} hours at room temperature, and are becoming increasingly popular in optical communications. It is being adopted as a light source for In order to extend the lifespan of this light-emitting device, it is necessary 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 spots, lines, dark spots, etc. The major success factors are that the reflective end face was protected with a dielectric film to prevent end face corrosion.

A double heterostructure with an oscillation wavelength in the 8000 Å band.
Ga _1-x Al _x As semiconductor laser devices have 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 mixing ratio x of Ga _1-x Al _x As increases, the segregation coefficient decreases and the ionization energy increases, so in laser elements using such Si and Sn, it is necessary to maintain a sufficient carrier concentration in the cladding layer. 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, Te, which has a large segregation coefficient, acts as an n-type impurity.
is often used. This Te has a large segregation coefficient and has the effect of increasing the carrier concentration, but is not suitable for obtaining good crystallinity. That is, when a large amount of Te is added, it is difficult to obtain a crystal with good flatness, and when the carrier concentration is 3×10 ¹⁸ cm ^-3 or more, the surface of the grown crystal takes on a terrace-like morphology. Further, even if the amount added is less than that, a wavy shape is often exhibited when the carrier concentration is 5×10 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 5×10 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 Te is added, the flatness of the active layer also deteriorates, resulting in an increase in scattering loss. This growth form includes many defects due to the segregation of Te at the interface between the n-type cladding layer and the active layer. These defects have a very large effect on the life characteristics of the semiconductor laser.

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

FIG. 1 is a cross-sectional view of a conventional semiconductor laser device used in this example. This device consists of an n-type GaAs substrate 2, an n-type Ga _0.67 Al _0.33 As cladding layer 3, an Si-doped n-type Ga _0.93 Al _0.07 As active layer 4, and a Ge
A P-type Ga _0.67 Al _0.33 As cladding layer 5 doped with Ge and a P-type GaAs cap layer 6 doped with Ge are successively grown by liquid phase growth, followed by CVD (chemical
An Al ₂ O ₃ film 7 is formed by vapor deposition (vapor phase growth accompanied by a chemical reaction), a band-shaped window 9 is formed in the film 7 by photolithography, and P-type electrodes 8 and n-type electrodes are formed at the upper and lower ends, respectively. This is an oxide film strip type semiconductor laser device with a double heterostructure provided with a type electrode 1. Two types of laser devices were fabricated in which Si and Te were added as impurities to the n-type cladding layer 3. 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 elements were driven at 50° C. with an output of 5 mW on one side, the driving current for the radar element at some initial driving 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 Figure 2, it was found that the element with Te added had a faster deterioration rate.

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, Te
It is necessary to use the same method, 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 Te-doped cladding layer.

In order to achieve the above object, the present invention grows a P-type cladding layer or a light guide layer on which a good crystal can be obtained relatively easily on a substrate, an active layer is formed on top of the P-type cladding layer, and Te is doped on top of the active layer. It is characterized by growing a non-containing buffer layer and a Te-doped n-type cladding layer to suppress deterioration caused by defects occurring at the interface between the active layer and the Te-doped n-type cladding layer, thereby achieving a longer life. .

If the Te-doped n-type cladding layer is grown before the active layer, it is difficult to obtain a well-planar Te-doped n-type cladding layer, and the planarity of the active layer becomes poor. , scattering loss increases. Also
When an active layer is grown next to a Te-doped n-type cladding layer, defects occur at the interface between the n-type cladding layer and the active layer, shortening the life of the device. Te
If we grow an n-type buffer layer that does not contain Te next to the doped n-type cladding layer and then grow the active layer on top of it,
The interface between the Te-doped n-type cladding layer and the n-type buffer layer, which contains defects caused by Te, is not in contact with the active layer, so it has the effect of suppressing deterioration, but the crystallinity is not good.
Since the active layer is grown after the Te-doped n-type cladding layer, the crystallinity of the active layer is inhibited.

In the present invention, first, the P-type cladding layer is grown before the active layer, and the Te-doped n-type cladding layer, which has problems with crystallinity and flatness, is grown after the active layer. Improved crystallinity and flatness. Second, after the active layer
After growing the buffer layer without doping Te.
Deterioration can be further suppressed by growing a Te-doped n-type cladding layer and separating the Te-doped n-type cladding layer, which contains defects caused by Te, from the active layer, which promotes deterioration due to recombination of electrons and holes. There is. 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 is p-type. As a type, it is necessary to form a Pn junction between the buffer 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 one 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 Ga _0.45 Al _0.55 As cladding layer 2 is formed thereon.
3, Ge-doped P-type Ga _0.82 Al _0.18 As active layer 2
4, Si-doped n-type Ga _0.87 Al _0.13 As buffer layer 3
0, Te-doped n-type Ga _0.45 Al _0.55 As cladding layer 25 and Te-doped n-type GaAs cap layer 26 are successively grown by liquid phase growth, and then n-type electrode 1 and P-type electrode 8 are formed by vapor deposition or the like. . In this embodiment, the current is narrowed by the current limiting layer 22, and the active layer 24 and buffer layer 30 are grown to be thickest at the center above the V-shaped groove, so that the effective A refractive index difference is formed.

In the above configuration, light within the active layer 24 is effectively guided by the refraction difference and collected at the center of the layer, 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 the n-type GaAs current limiting layer 22 is used,
The diffusion length of holes in n-type GaAs is 2 μm or less, which is smaller than the thickness of a normally used current limiting layer, so electrons injected into the current limiting layer do not penetrate through that layer, effectively confining the current. I can do it.

When a device according to this embodiment is actually manufactured, 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 a significant improvement was seen compared to a device in the same wavelength band in which a conventional Te-doped n-type cladding layer was grown before the active layer.

In the embodiments described above, the active layer is grown directly on the P-type cladding layer, but it goes without saying that the present invention can also be applied to the case 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 one 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)

[Scope of Claims] 1. In a double heterojunction semiconductor laser device made of a mixed crystal containing at least three elements, Ga, A, and As, a P-type cladding layer active layer, a buffer layer, an n-type cladding layer, and a p-type cladding layer are formed on a substrate. The layers are laminated sequentially, and the n
Te is added as an impurity to the type cladding layer, and Te is added between the active layer and the n-type cladding layer.
1. A semiconductor laser device characterized in that the buffer layer is interposed without addition of. 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.