JPS6258679B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a highly reliable semiconductor laser device that produces stable fundamental transverse mode oscillation with high optical output in the center of an active layer.

Semiconductor laser devices used in optical fiber communications, optical video disks, optical measurement devices, etc. are generally manufactured by the following method. That is, an N-type light and carrier confinement layer, an N-type or P-type active layer, a P-type light and carrier confinement layer, and an N-type cap layer are formed on an N-type semiconductor substrate having a (100) crystal plane by liquid phase epitaxial deposition. After continuous growth using a growth method, a striped ohmic contact layer having a predetermined width and penetrating the N-type cap layer and reaching a part of the P-type light and carrier confinement layer is formed. <110
> Provided in the crystal axis direction. Thereafter, electrodes are deposited on the surface of the N-type cap layer and the back surface of the N-type semiconductor substrate, respectively, to manufacture a semiconductor laser device. In the semiconductor laser device manufactured by this method, there is a difference of n between the refractive index n _a of the N-type or P-type active layer and the refractive index n _c of the N-type and P-type light and carrier confinement layers sandwiching it. Since there is a relationship of _a > n _c , recrystallization of carriers injected from the electrode occurs within the N-type or P-type active layer, and light corresponding to the energy gap of the active layer is confined within the active layer. The confinement effect of this confined light in the direction perpendicular to the active layer (vertical direction) becomes more significant as the above-mentioned refractive index difference increases, but the confinement effect in the direction horizontal to the active layer (lateral direction) is due to the ohmic contact layer. Since the spread of the injected carriers from the N-type semiconductor substrate to the N-type semiconductor substrate is large and ineffective, there are disadvantages such as an increase in the oscillation threshold current value, fluctuations in the oscillation transverse mode, difficulty in high optical output laser oscillation, and a lack of long-term reliability. will have the following.

As a conventional technology that improves these drawbacks, (a) a double hetero structure in which a stripe-shaped concave or convex part is provided on a semiconductor layer substrate of one or more layers, and one side is bonded to this and the other side is bonded to another semiconductor layer; Method of stabilizing the oscillation mode by providing a triple layer
110489) or (b) forming striped recesses on the surface of the semiconductor substrate and providing a guide layer and a photon confinement layer above and below the layer that will become the active region during liquid phase epitaxial growth. Method for obtaining transverse mode (Japanese Patent Application Laid-Open No. 55-123189), and (c)
A method for obtaining stable fundamental mode oscillation at the center of a semiconductor laser by making the center of the semiconductor laser a waveguide structure and the other region a non-waveguide structure for the laser oscillation wavelength (Japanese Patent Application Laid-Open No. 108791/1983) , and (d)
A striped laminate _of InP and In _{1 -X Ga} Embedded semiconductor device method (JP-A-Sho)
55-162288). In the conventional examples (a) and (b) above, the layer thickness is different between the striped concave portion and the surrounding area of the N-type light and carrier confinement layer provided on the N-type semiconductor substrate, resulting in an effective refractive index difference. , lateral confinement is performed. However, when growing an N-type light and carrier confinement layer by liquid phase epitaxial growth in the striped recesses of an N-type semiconductor substrate,
Since meltback on the surface of the N-type semiconductor substrate is impossible, a large number of crystal defects are induced at the interface between the striped recesses and the N-type light and carrier confinement layer. In addition, since the crystal growth of the N-type light and carrier confinement layer starts from the bottom corner of the striped recess, the center of the striped recess becomes a source of dislocation or internal stress due to the concentration of impurity atoms or lattice defects in the crystal. It forms a boundary surface, and during oscillation operation, a defect region called a <110> dark line defect occurs along the stripe at the center of the striped recess, resulting in failure in an extremely short period of time, which is a serious drawback in terms of reliability. In addition, in the conventional examples (c) and (d) above, the active layer is surrounded by semiconductor crystals with a refractive index smaller than that of the active layer, which is highly effective for confining light and carriers in the lateral direction. It is technically extremely difficult to precisely control the width of the active layer by etching the N-type or P-type active layer, the P-type light and carrier confinement layer, and the N-type cap layer, which have different etching rates, under the same conditions. However, it has the disadvantage that it is impossible to realize a stable oscillation transverse mode with good reproducibility.

The present invention eliminates these drawbacks and obtains a semiconductor laser device with a simple structure, high output, and stable fundamental transverse mode oscillation that continues for a long period of time.
The periphery of the striped convex portion of the N-type light and carrier confinement layer formed on the N-type semiconductor substrate is filled with the same semiconductor crystal as the N-type semiconductor substrate to form the striped groove of the N-type semiconductor substrate. Features.

That is, the present invention provides an oxide film with openings on the surface of a first N-type light and carrier confinement layer using an N-type semiconductor crystal as a substrate, and chemically etches the first N-type light and carrier confinement layer to open the first N-type light and carrier confinement layer. The exposed portion in the hole is removed to form a striped convex portion having a predetermined width, and the concave portion around the stripe is filled with the same N-type semiconductor layer as the N-type semiconductor substrate using the oxide film as a mask. After that, the oxide film is removed, and the surface of the N-type semiconductor layer including the striped first N-type light and carrier confinement layer is slightly melt-backed and a second N-type light and carrier confinement layer is formed. An N-type or P-type active layer, a P-type light and carrier confinement layer, and an N-type cap layer are successively grown by liquid phase epitaxial growth to correspond to the striped first N-type light and carrier confinement layer. After forming an ohmic contact layer having a depth that penetrates the N-type cap layer and reaches a part of the P-type light and carrier confinement layer, an ohmic contact layer is formed on the surface of the N-type cap layer and the back surface of the N-type semiconductor substrate, respectively. This is a semiconductor laser device covered with electrodes.

Next, embodiments of the present invention will be described with reference to the drawings.
1 to 4 are cross-sectional views showing the manufacturing process of a semiconductor laser device according to the present invention. FIG. 1 shows a first N-type Ga _{1-x Al} 1 is a diagram showing a state in which an oxide film 3 such as Al ₂ O ₃ having openings is provided on the surface of the N-type Ga _1-x Al _x As light and carrier confinement layer 2 of No. 1. FIG. Figure 2 shows the first hole exposed in the above hole by chemical etching.
N-type Ga _1-x Al _x As light and carrier confinement layer 2
FIG. 3 is a diagram showing a state in which a part of the N-type GaAs substrate 1 is removed to form a convex portion (channel) having a predetermined stripe width. Figure 3 shows the above condition.
Using an oxide film 3 such as Al ₂ O ₃ as a mask, the recesses surrounding the striped convex portions are filled with an N-type GaAs buried layer 4 having the same carrier concentration and mobility as the N-type GaAs semiconductor substrate 1. FIG. FIG. 4 is a diagram showing the completed state of the semiconductor laser device of the present invention. The process from FIG. 3 to FIG. 4 is that after the N-type GaAs buried layer 4 described above is formed, the oxide film 3 such as Al ₂ O ₃ is removed, and the striped first N-type
Ga _{1-x Al}
a Ga _1-x Al _x As light and carrier confinement layer 5;
This N-type or P-type Ga _1-y Al _y As active material has an Al composition ratio (y) smaller than the Al composition ratio (x) of the N-type Ga _(1-x ) Al _x As light and carrier confinement layer. Layer 6 and P type
Ga _(1-x) Al _x As light and carrier confinement layer 7;
A GaAs cap layer 8 is successively grown by liquid phase epitaxial growth. Next, corresponding to the striped first N-type Ga _1-x Al _x As light and carrier confinement layer 2, the P-type
After providing an ohmic contact layer 9 with a depth reaching a part of the Ga _1-x Al _x As light and carrier confinement layer 7 by diffusing Zn, a Cr alloy was used on the surface of the N-type GaAs cap layer 8. Electrode 10 and the N-type GaAs
Electrode 1 using GeNi alloy on the back side of semiconductor substrate 1
1 by vacuum evaporation to construct a semiconductor laser device.

The principle of oscillation operation of the semiconductor laser device of the present invention is as follows. That is, when a current is passed through the electrode 10 in the figure and a carrier is injected, the Al mixed crystal ratio (y) of the N-type or P-type Ga _1-y Al _y As active layer 6 changes to the second N-type Ga ₁ sandwiching it. _-x Al _x As light and carrier confinement layer 5 and P-type Ga _1-x Al _x As light and carrier confinement layer 7 are smaller than the Al mixed crystal ratio (x), so recombination of injected carriers mainly occurs. The longitudinal direction of a portion of the light generated within the N-type or P-type Ga _{1 -y} Al _{y As} active layer 6 and having a high refractive index. Confinement is performed (in the direction perpendicular to the active layer 6). On the other hand, it consists of a striped first N-type Ga _1-x Al _x As optical and carrier confinement layer 2 and a second N-type Ga 1 _{- x} Al
Since the layer thickness of the light and carrier confinement layer, which has the role of confining the light seeped out from the Ga _1-y Al _y As active layer 6, is thinner in the peripheral part than in the stripe part, the light seeped out in the peripheral part of the stripe is thinner than the stripe part. are all absorbed into the N-type GaAs buried layer 4. Therefore, the refractive index of the active layer 6 is effectively smaller in the peripheral portion than in the stripe portion, so that light is confined in the lateral direction. The striped first N-type Ga _1-x Al _x As light and the light confined within the N-type or P-type Ga _1-y Al _y As active layer 6 in the region corresponding to the carrier confinement layer 2 are When the amplification gain becomes larger than the internal loss, the laser beam is emitted to the outside.

As described above, in the semiconductor laser device according to the present invention, the striped grooves of the N-type semiconductor substrate are
Because the same material as the N-type semiconductor substrate is embedded around striped protrusions (channels) previously provided on the N-type semiconductor substrate, <110> dark line defects occur within the channels. It is possible to avoid the occurrence of dislocations and internal stress due to the concentration of impurity atoms and the like. In addition, since the striped channels described above are mainly produced by chemically etching only one layer of the first N-type Ga _1-x Al _x As layer provided on the semiconductor substrate, the stripe width can be easily controlled and reproducible. Rich.
Therefore, the present invention provides a method for manufacturing a semiconductor laser device that can maintain stable transverse mode laser light oscillation in an active layer corresponding to the stripe width for a long period of time, and has a simple structure and high reliability. .

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are diagrams showing the manufacturing process of a semiconductor laser device according to the present invention, respectively. DESCRIPTION OF SYMBOLS 1... N-type semiconductor substrate, 2... First N-type light and carrier confinement layer, 3... Oxide film, 4... N-type semiconductor buried layer, 5... Second N-type light and carrier confinement layer, 6... N-type or P-type active layer, 7... P-type light and carrier confinement layer, 8... N-type cap layer, 9
...Ohmic contact layer, 10 and 11...electrode.

Claims (1)

[Claims] 1. An oxide film with openings is provided on the surface of a first N-type light and carrier confinement layer using an N-type semiconductor crystal as a substrate, and the oxide film is exposed in the opening of the first N-type light and carrier confinement layer. After removing the oxidized portion by etching to form striped convex portions, and filling the concave portions around the striped convex portions with the same N-type semiconductor layer as the N-type semiconductor substrate using the oxide film as a mask, The film is removed, and a second N-type light and carrier confinement layer and an N-type or P-type active layer are formed on the striped first N-type light and carrier confinement layer and the surrounding N-type semiconductor layer. , a P-type light and carrier confinement layer, and an N-type cap layer are sequentially formed to form a striped first N
After providing an ohmic contact layer that corresponds to the type light and carrier confinement layer, penetrates the N-type cap layer, and reaches a part of the P-type light and carrier confinement layer, the surface of the N-type cap layer and the N-type contact layer are formed. 1. A method of manufacturing a semiconductor laser device, comprising depositing electrodes on each back surface of a semiconductor substrate.