JPH0157515B2 - - Google Patents

Description

1. A semiconductor laser device characterized in that it is formed by laminating an n-type cladding layer 25.

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to semiconductor laser devices, particularly Ga _1-X
This invention relates to a semiconductor laser device made of Al _x As and having a double heterojunction structure.

<Conventional technology and ^its problems> Ga _{1- X} ^Al It has been reported that it has a long lifespan, and it is being used as a light source for optical communications. In order to achieve a longer lifetime for light emitting devices, 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 are that the reflective end face was protected with a dielectric film to prevent end face corrosion.

Ga _{1-X Al}
Si, which has a relatively small segregation coefficient as an n-type impurity,
Impurities such as Sn can be used. However, as the Al mixed crystal ratio of Ga _{1-X Al} It is difficult to do so. 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, is used 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. In other words, when a large amount of Te is added, it is difficult to obtain a crystal with good flatness, and the carrier concentration is 5.
When it is more than ×10 ¹⁸ cm ^-3 , the surface of the grown crystal takes on a terrace-like morphology. In addition, even if the amount added is less than that, the carrier concentration will be 5×
When the temperature is 10 ¹⁷ cm ^-3 or higher, it often takes on a wavy shape.

As described above, it has been difficult to obtain a laser element having a clad layer with a carrier concentration of 5×10 ¹⁷ cm ^-3 or more and a crystal layer with good flatness. 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 device.

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 experiment. This device consists of an n-type Ga _0.67 Al _0.3 As cladding layer 3 on an n-type GaAs substrate 2, an n-type Ga _0.93 Al _0.07 As active layer 4 doped with Si, and a p-type Ga _0.67 Al _0.33 As cladding layer 5 doped with Ge. , a Ge-doped p-type GaAs cap layer 6 is continuously grown by liquid phase growth, and then 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 on the film 7 by photolithography, and a p-type electrode 8 and an n-type electrode are formed at the upper and lower ends, respectively. This is an oxide film stripe type semiconductor laser device with a double heterojunction structure in which an electrode 1 is provided. 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 coated 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 currents 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 for 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.

Furthermore, there is a conventional CSP laser with an internal stripe structure, such as that disclosed in Japanese Patent Application Laid-Open No. 52-90280.
This structure has a Zn diffusion layer on the surface of an n-GaAs substrate and a p-GaAs region of the opposite conductivity type, and an active layer sandwiched between cladding layers is disposed on this substrate. Also
Striped grooves are formed through the Zn diffusion layer.
This part serves as a current path.

In such a structure, the light generated in the active layer is not absorbed into the substrate in the striped grooves, but is absorbed into the Zn diffusion layer and the substrate outside the striped grooves.
In this way, current confinement and optical waveguide effects are performed on the GaAs substrate side.

However, this structure has the following practical problems.

Since the diffusion length of electrons, which are minority carriers, in the Zn diffusion layer is as long as approximately 3 μm, the thickness of the Zn diffusion layer must be greater than that in order to achieve current confinement. Therefore, the width of the rectangular stripe groove 7 is set to 5 μm.
It is difficult to make the threshold current less than or equal to 1, and the reactive current that spreads outside the laser oscillation region cannot be ignored, so the threshold current cannot be made sufficiently small. Also, the transverse mode tends to become unstable during high output operation.

The present invention eliminates the above-mentioned drawbacks of the conventional CSP laser, and provides a long-term stable laser with a low oscillation threshold current Ith, a high quantum differential efficiency ηD, and a refractive index waveguide mechanism with good waveguide characteristics. Operating life characteristics Ga _1-X
The purpose of the present invention is to provide a semiconductor laser device having an Al _x As-based double heterojunction structure.

<Means for solving the problems> In order to achieve the above object, the present invention provides Ga _1-X
In a semiconductor laser device having a double heterojunction structure made of Al _x As, an n-type GaAs current limiting layer is deposited on a p-type GaAs substrate.
The cross section of the GaAs current limiting layer, which serves as a current path, is approximately V.
A trench with a depth reaching the p-type GaAs substrate is formed in the form of a letter-shaped stripe penetrating this n-type GaAs current limiting layer, and on top of this is a p-type cladding layer, an active layer on top of that, and a trench on top of that. The structure is such that an n-type crat layer formed using Te as an impurity is laminated on the top.

<Function> With the above configuration, in the semiconductor laser device of the present invention, the active layer is more active than the narrow current path opened in the V-shaped striped groove located directly below the active layer. Since carriers are injected into the layer and the lateral spread of the current is suppressed, the current is efficiently constricted into a very narrow striped region. In addition, in the present invention, by setting the current limiting layer to be an n-type layer, minority carriers become holes, and their diffusion length becomes shorter than that of electrons. Even in the limiting layer, current is constricted without turning on during light irradiation (Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a cross-sectional configuration diagram showing the above embodiment.
In this embodiment, after growing an n-type GaAs current limiting layer 22 on a p-type GaAs substrate 21, the current limiting layer 22 is
A V-shaped groove 27 is formed in the current limiting layer 22 and the V-shaped groove 27.
P-type Ga _0.45 Al _0.55 doped with Zn on the shape groove 27
As cladding layer 23, n-type Ga _0.88 doped with Si
Al _0.12 As active layer 24, n-type Ga _0.45 doped with Te
Al _0.55 As cladding layer 25, Te doped n-type
The GaAs cap layer 26 is continuously grown in liquid phase,
N-type electrode 1 and p-type electrode 8 at the upper and lower ends, respectively.
This is a semiconductor laser device provided with.

For the V-shaped groove 27, an etching solution with a mixing ratio of ammonia water, hydrogen peroxide solution, and water of 1:1:50 is used.
Formed by photolithography.

The thickness of the active layer 24 is grown so that it becomes the largest in the central part above the V-shaped groove 27.
An effective refractive index difference is provided in the lateral direction of 4.

In the above configuration, light within the active layer 24 is effectively guided by the refractive index 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 and is absorbed by the current limiting layer 22, and as a result, electron and hole pairs are excited in the current limiting layer 22. The current will flow within the layer 22 and cannot be effectively confined; however, in this embodiment the active layer 2
4, an effective refractive index distribution is provided, and the current limiting effect of the current limiting layer 22 can be fully exhibited.

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,
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 manufactured, the threshold current of the device will be 30mA to 50mA at 25℃.
The oscillation wavelength was approximately 790 nm.

Note that a light guide layer may be formed between the cladding layer and the active layer in the above embodiments.

Next, the life characteristics of the above embodiment will be explained based on experimental examples.

In this experimental example, changes over time in the driving current of the device according to the above embodiment and the device using an n-type substrate as shown in FIG. 4 were determined and compared. The device shown in FIG. 4 used for comparison has a V-shaped groove 27 on an n-type GaAs substrate 2, on which a Te-doped n-type Ga _0.45 Al _0.55 As cladding layer 33 and a Si-doped n-type Ga _0.88 Al cladding layer 33 are formed. A _0.12 As active layer 34, a p-type Ga _0.45 Al _0.55 As cladding layer 35 doped with Zn, and a p-type GaAs cap layer 6 doped with Ge are successively grown in a liquid phase, and further as in the device shown in FIG.
An oxide film stripe 9 is formed from a CVD Al ₂ O ₃ film 7, and electrodes 1 and 8 are provided at the upper and lower ends, respectively. In this way, when an n-type GaAs substrate is used and a current limiting layer is provided on the substrate side as in the above embodiment, the current confining layer becomes a p-type.
However, the diffusion length of electrons, which are minority carriers, in such a p-type GaAs current limiting layer is larger than the normal current limiting layer thickness, that is, 5 μm or more, and current limiting cannot be performed effectively. Therefore,
As shown in FIG. 4, an oxide film stripe 9 is provided to limit the current. When this device was actually manufactured, the threshold current of the device was 40 mA to 60 mA at 25°C, and the oscillation wavelength was approximately 790 nm. The end faces of the device according to the above embodiment shown in FIG. 3 and the device shown in FIG. 4 are each covered with an Al ₂ O ₃ film.

When these elements were driven at 50° C. and 1 mW output, the drive current for some initial drive currents showed changes over time as shown in FIG. In FIG. 5, the vertical axis represents the drive current, and the horizontal axis represents time, where the solid line A is for the device shown in FIG. 3, and the broken line B is for the device shown in FIG. 4. Solid line A
As shown, no deterioration is observed in the device according to the above example, but in the device shown in FIG. 4, in which the active layer is grown on the n-type cladding layer doped with Te, there is significant deterioration as indicated by the broken line B.

In addition to the embodiment shown in FIG. 3, the present invention can be applied to semiconductor laser devices having any structure such as oxide film stripes, planar stripes, neutron irradiation stripes, etc. which are commonly used. That is, it can be implemented by using a p-type GaAs substrate instead of the conventionally used n-type GaAs substrate. Also, when using a light guide layer,
A Te-doped n-type light guide layer can be grown and applied next to the active layer.

As described above, the above embodiment has the following effects in addition to the above.

The structure is such that a p-type cladding layer, which is easy to obtain relatively good crystals, is grown first, and then an active layer and a Te-doped n-type cladding layer are grown on top of it, so that the interface between the active layer and the n-type cladding layer is The density of defects generated in the process is reduced.

As a result, deterioration caused by the above-mentioned defects is reduced, and the life of the device can be extended.

Since the liquid wavelength of the Te-doped layer does not affect the flatness of the active layer, the scattering loss and threshold current due to the wavy morphology are reduced compared to the conventional method.

<Effects of the Invention> As described above, according to the present invention, n
Since the structure has a deposited type current limiting layer, the layer thickness can be made thinner than when using a p-type current limiting layer, and as a result, the expansion of the stripe width when opening a current path is limited. As a result, current confinement in a narrow width becomes possible, and laser oscillation with a low threshold current becomes possible.

Furthermore, according to the present invention, the n-type cladding layer laminated on the active layer is formed using Te as an impurity, thereby reducing the density of defects occurring at the interface between the active layer and the n-type cladding layer. As a result, a stable semiconductor laser with improved lifetime characteristics can be obtained.

[Brief explanation of drawings]

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 showing an embodiment of the present invention. Fourth
The figure is a cross-sectional configuration diagram of a conventional semiconductor laser device used in an experimental example. FIG. 5 is a characteristic diagram showing changes over time in the driving current of the elements shown in FIGS. 3 and 4. FIG. DESCRIPTION OF SYMBOLS 1, 8... Electrode, 21... Substrate, 22... Current limiting layer, 23, 25... Clad layer, 24... Active layer.

Claims (1)

[Claims] In a semiconductor laser device having a double heterojunction structure made of 1 Ga _1-X Al _X A _S system, an n-type GaAs current limiting layer 22 is deposited on a p-type GaAs substrate 21, The GaAs current limiting layer 22 has n-type GaAs stripes with a roughly V-shaped cross section that serves as a current path.
The p-type GaAs substrate 2 passes through the current limiting layer 22.
A groove 27 with a depth of 1.1 mm is formed, on which a p-type cladding layer 23 is formed, an active layer 24 is formed on top of this, and Te is formed as an impurity on top of the active layer 24.