JPS6125233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a striped semiconductor laser.

Multilayer heterostructure semiconductor lasers such as (Al/Ga)As have a low threshold current value and can oscillate with high efficiency even at room temperature, so they are used for applications such as optical fiber communications.

Various striped structures have been devised in order to operate this type of laser with a current value as small as possible and to cause it to oscillate in a single transverse mode or in a state close to this mode.

However, the various striped structures conventionally used have the following common drawbacks and are therefore unsatisfactory in practice. That is, when the stripe width is about 20 μm or more, higher-order transverse modes easily oscillate, causing problems such as waveform distortion and increased output intensity fluctuations (output noise) when direct modulation is performed. On the other hand, when the stripe width is reduced to about 8 μm or less, the threshold current density increases rapidly, and
The laser beam intensity that can be output without optical damage to the end face is reduced.

Therefore, the stripe width is usually 10μm or more, 20μm or more.
The stripe width is set to a range of .mu.m or less, but if the stripe width is within this range, abnormalities appear in various characteristics of the semiconductor laser. For example, the output does not increase linearly with the excitation current, a bend occurs in the excitation current-optical output curve, and the waveform during direct modulation is significantly distorted. Further, in many cases, when the current value is near or above the above-mentioned bending, abnormality or deterioration of the characteristics such as an increase in the oscillation light spectrum width occurs.

Therefore, in order to eliminate the abnormalities in the characteristics exhibited by the conventional striped semiconductor laser, it is necessary to stabilize the optical waveguide in the horizontal and lateral directions. For this purpose, for example, a spatial distribution of refractive index or gain (or loss) fixed to the crystal is formed horizontally within the active layer,
The laser light may be confined within the stripe portion by the optical waveguide. For example, if a P-type impurity is diffused into the striped part of the active layer of a multilayer double hetero, and the refractive index of this material is made higher than the refractive index of the outside, the introduced refractive index distribution will stabilize the light guide. It is described in Patent Application No. 51-26440 that waves can be generated, and the effect has been experimentally confirmed. However, in the method described in the above patent, it is necessary to diffuse the impurity to reach the depth of the active layer, and the impurity concentration must be adjusted to create an optimal refractive index difference to stabilize the oscillation mode. Since control is required, it involves difficulties in terms of manufacturing technology. In order to eliminate these drawbacks and create a semiconductor laser with a stable oscillation mode with good reproducibility, impurities are deeply diffused in only a predetermined region within the stripe beyond the active layer, so that the effective refractive index inside the stripe is higher than that outside the stripe. A semiconductor laser with a raised structure has been devised. (Japanese Patent Application No. 52-88196) In a semiconductor laser with such a structure, it is necessary to diffuse impurities deeper into a part of the impurity diffusion region than in other parts. However, there was no way to realize a semiconductor laser with this structure.
However, in the double diffusion method, the impurity is diffused twice, making it difficult to control the impurity concentration and diffusion depth.

The present invention eliminates the above-mentioned drawbacks, provides a method for selectively and deeply diffusing only a predetermined portion of an impurity diffusion region, and also provides a method for selectively and deeply diffusing only a predetermined portion of an impurity diffusion region.
88196) can be easily realized. That is, this is a method in which impurities are diffused in advance to a predetermined depth in a region where impurities are to be diffused, and then only a predetermined region of the diffusion region is covered with a dielectric film such as a SiO ₂ film and then heat treated again. According to this method, since a dielectric film is formed on the surface, the surface condition of the semiconductor changes, and the diffusion of impurities is promoted or suppressed in the region under the dielectric film, and regions with different diffusion depths are partially formed. Therefore, a semiconductor laser having a structure in which impurities are deeply diffused to the active layer only in a predetermined region within the stripe can be obtained.

EMBODIMENT OF THE INVENTION An example of implementation of the present invention will be specifically described below using the drawings.

Approximately 3 μm thick on n-type GaAs substrate 10 by liquid phase growth method
n-type _{A1 0.3} Ga _00.7 As layer 11 with a thickness of about 0.2 μm; n-type GaAs active layer 12 with a _thickness of about 2 μm; P-type with a thickness of about 2 μm.
An A1 _{0.3 Ga 00.7} As layer 13 and _an n-type GaAs layer 14 with a thickness of approximately 1 μm are grown.

A width created in the SiO ₂ film 15 on the fourth layer in a direction perpendicular to the cleavage plane using photoresist technology.
Zn1 through stripes with intervals of 15 μm and 250 μm
6 is diffused at 600° C., and its diffusion front 17 is controlled in the middle of the third layer (FIG. 1).

Next, after removing the SiO ₂ film 15 for Zn diffusion and applying a 3000 Å SiO ₂ film as a dielectric coating over the entire surface of the fourth layer, use photoresist technology to cross the front stripe (not necessarily at right angles). 50μm
A striped SiO ₂ film 18 with a width of 10 μm is formed at intervals (FIG. 2).

This wafer is placed in a quartz ampoule with a high degree of vacuum.
When sealed at 10 ^-6 Torr or less and heat treated in a 750°C furnace for 3 hours, Zn is removed in the area where the SiO ₂ film 18 remains.
quickly diffuses, and its front 19 reaches the first layer. On the other hand, since the Zn in the area without the SiO ₂ film 18 hardly moves, diffusion regions with different diffusion depths are formed. The SiO ₂ film 18 is removed, a P-type ohmic contact 20 and an n-type ohmic contact 21 are formed, and individual semiconductor lasers are obtained by cleavage (FIG. 3).

The shape of the SiO ₂ film 18 is not limited to that shown in FIG. 2, but may be shown in FIG. 4, and the shape is arbitrary. however,
Since the increase in refractive index caused by Zn pushed into the active layer is between 1% and 0.01%, the volume of the Zn diffusion part is determined so that this increase contributes to the increase in the refractive index of the entire semiconductor laser. This results in a single mode laser.

In the above example, Zn was diffused as an impurity.
Although we have explained the case of a GaAs-A1GaAs double heterojunction semiconductor laser, other crystal materials,
For example, it can be applied to other crystal materials such as InGaAsP-InP, GaAsSb-A1GaAsSb, and impurities other than Zn such as Sb, and similar effects can be obtained. Furthermore,
Although the SiO ₂ film is used as an example of the dielectric coating, the same effect can be achieved by using other dielectric coatings by slightly changing the structure or diffusion conditions. For example, if an Al ₂ O ₃ film is used instead of a SiO ₂ film, impurity diffusion is suppressed directly under the Al ₂ O ₃ film, so it is necessary to cover areas other than those where deep diffusion depth is required with the Al ₂ O ₃ film. The same results as in the case of SiO ₂ film can be obtained.

As explained above, according to the present invention, diffusion regions with different diffusion depths with precisely controlled impurity concentrations can be easily obtained, so that impurities are partially diffused only in predetermined regions within the stripes of the active layer. A semiconductor laser with such a structure can be easily obtained with good reproducibility.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing how Zn is selectively diffused into the semiconductor laser wafer used in the present invention.
The figure is a plan view showing a state in which a SiO ₂ film is selectively applied to this semiconductor laser wafer, FIG. 3 is a cross-sectional view of a semiconductor laser obtained by the present invention, and FIG. FIG. 2 is a plan view showing a SiO ₂ film applied to a structure different from that shown in the figure. In the figure, 10... n-type GaAs substrate, 11...
...N-type _{A10.3 Ga00.7} As layer, _{12 ...Active layer made of n-type GaAs, 13...P-type A10.3 Ga00.7 As layer , 1}
4...n-type GaAs layer, 15...SiO ₂ for Zn selective diffusion
Film, 16...Diffusion region of selectively diffused Zn, 17
...Front of Zn diffusion region, 18...SiO ₂ film,
19... Deeply diffused Zn front, 20...
P-type ohmic contacts and 21...indicate n-type ohmic contacts, respectively.

Claims (1)

[Claims] 1. In a method for manufacturing a double heterojunction semiconductor laser in which an active layer is sandwiched between cladding layers having a wider bandgap than the active layer, the double heterojunction semiconductor laser has a conductivity type opposite to that of the active layer in advance in a stripe shape. After diffusing the impurity, a part of the surface of the diffusion region is covered with a dielectric film, and the semiconductor laser wafer is heat-treated in a vacuum to partially introduce the impurity into the striped active region. A method for manufacturing a semiconductor laser characterized by comprising: