JPS5914912B2 - Manufacturing method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor laser, particularly a semiconductor laser having a buried heterostructure.

Various proposals have been made for the structure of semiconductor lasers that can oscillate at low currents and have good optical properties, among which semiconductor lasers with buried heterostructures are particularly superior in principle. .

On the other hand, recently, as a light source for optical communication using quartz fiber, In
Demand for GaASP-InP double heterostructure semiconductor lasers has increased, and InGaASP-InP semiconductor lasers with low threshold values and good optical characteristics have become necessary. However, so far, this type of InGaASP-InP' with low threshold and good optical properties has not been developed.
A θ semiconductor laser has not been realized, and no effective manufacturing method has been found for a buried heterostructure semiconductor laser, so a low threshold semiconductor laser has not been realized.

Therefore, the object of the present invention is to
An object of the present invention is to provide an effective method for manufacturing a semiconductor laser having a 5-buried heterostructure.

A semiconductor laser with a buried heterostructure of this type is shown in FIG.

This figure 1 shows a semiconductor laser having a buried heterostructure cut along a plane perpendicular to the propagation direction of the laser beam. In this figure, 1 is an n-type engineered nP substrate, and 2 is an n-type or undoped In
GaASP layer, 3 is P-type InP layer, 4 is p-type InP
layer 5 is an insulating layer such as SiO2 or Si3N4, 6
and 5T indicate p-side and n-side electrodes, respectively. In the semiconductor laser having the buried heterostructure shown in FIG. 1, since the InGaASP layer 2, which is the laser active region, has barriers against carriers on all its sides, the diode 30 The current flowing through the InGaASP is concentrated in this layer 2, and the injected electrons and holes are confined in this layer 2 without spreading laterally, making it possible to obtain high quantum efficiency.
All sides of the layer 2 have a lower refractive index.
and is surrounded by the lnP layers 353 and 4,
Good optical confinement can be achieved and good optical and electrical properties can be obtained. However, a semiconductor laser with such a buried heterostructure
Conventionally, it has been manufactured as shown in FIGS. 2a to 2d.

That is, as shown in FIG. 2a, first, n-type or non-doped InG is grown on one main surface of an n-type 1nP substrate 1 by a normal liquid phase epitaxial growth method.
The aASP layer 2 and the p-type 1nP layer 3 are sequentially grown.

Then, on the p-type 1nP layer 3, an insulating film such as a SiO2 film or a Si3N4 film is deposited to a thickness of about 0.5 μm by a sputtering method, and this film is applied in the 110> direction of the substrate. Excluding the extending stripe portion with a width of about 5 μm, the p-type 1nP layer 3 was removed by ordinary photolithography until the surface was exposed, and the p-type 1nP layer 3 was removed using the remaining film as a mask. Death and InGaASP layer 2
, bromine-methanol solution or HC:CH3CO
With an etching solution having a composition of OH:H2O2=l:l:l, the n-type 1nP? After mesa etching is performed until the plate 1 is exposed, the remaining film is removed using HF or the like, as shown in FIG. 2b. Next, as shown in FIG. 2c, a p-type 1nP layer 4 is grown on the surface of the semiconductor crystal having the mesa structure shown in FIG. As seen in the DVC, this p-type 1nP
After forming an insulating layer 5 such as a SiO2 film or a Si3N4 film on the layer 4, the part facing the mesa part is selectively removed, and finally metal electrodes 6 and 7 are formed by vacuum evaporation or the like. That's what I do.

Conventional buried heterostructure semiconductor lasers are manufactured in this way. In particular, a process of directly growing p-type 1nY44 by liquid phase epitaxial growth on the surface of a semiconductor crystal having a mesa structure as shown in FIG. 2b. This results in the following disadvantages:

In other words, various types of impurities are generally deposited on the semiconductor surface exposed to the atmosphere, and when a 1np layer is grown directly on this surface as described above, these impurities are incorporated into the crystal and many types of impurities are deposited. This will result in defects. Furthermore, InP crystals have particularly poor thermal stability, and when exposed to high temperatures for long periods of time, P evaporates and a metamorphosed layer deficient in P is formed on the surface. A certain force ξDuring the above-mentioned liquid phase epitaxial growth, in order to bring the melt into contact with the crystal surface and hold it at a high temperature for a long time before the growth starts, such a metamorphic layer is formed and the crystal surface is Various defects also occur at the interface between the semiconductor laser and the grown layer, and these defects lower the quantum efficiency of the resulting semiconductor laser and shorten its lifetime. This invention aims to improve the above drawbacks of the conventional method. Immediately before growing a p-type 1nP layer by liquid phase epitaxy on the surface of the semiconductor crystal having a mesa structure, the mesa structure is enlarged using an InP melt. It melts back without deforming and removes impurities and metamorphosed layers on the crystal surface.

Hereinafter, one embodiment of the method of the present invention will be described in detail with reference to FIGS. 3a to 3d.

First, as shown in FIG. 3a, on one main surface of the n-type 1nP substrate 1, by the usual liquid phase epitaxial growth method,
InGaAS not doped with n-type or impurities
P layer 2, p-type 1nP layer 3}, and InGaASP layer 8 are grown in sequence.

Further, as in the conventional method, an insulating film such as an SiO2 film is used to obtain a mesa-structured semiconductor crystal as shown in FIG. 3b. Subsequently, a p-type 1nP layer 4 is grown on the surface of the mesa-structured semiconductor crystal by an eight-liquid phase epitaxial growth method. , it is brought into contact with a semiconductor crystal and melted back. With this meltback, NP is ＼ 3μ
The inventors have found through various experiments that the InP layer 3 under the InGaASP layer 8 is difficult to etch back because Ga dissolves into the In melt at this time when the InGaASP layer 3 is also etched back. It soon became clear. As a result, by adopting the structure shown in FIG. 3b, the mesa structure is not significantly deformed even when etching back with an In melt is performed, and the structure shown in FIG. 3c can be easily obtained. Next, an insulating layer 5 is deposited on the surface of the P-type 1 layer 4 grown in this way, and after this is selectively removed, metal electrodes 6 and 7 are formed and the arms are opened. The structure shown in FIG. 3D can be obtained in the same manner as in the prior art. The above implementation fl! Although this example uses an n-type 1nP substrate, it can also be applied to a p-type 1nP substrate, and is also effective for embedded light emitting diodes.
Furthermore, combinations of other materials having different solubility are also possible.

As detailed above, according to the present invention, an InGaASP layer of one conductivity type or not doped with impurities is formed on one main surface of an InP substrate of one conductivity type, an InP layer of the other conductivity type, and an InGaASP layer of the other conductivity type. Even if the layers are sequentially grown by liquid phase epitaxial method to form a mesa structure and then melted back immediately before the liquid phase epitaxial growth of the other conductivity type InP layer on the surface, the top layer is
Since it is an nGaASP layer, it is possible to leave the active region underneath, and since the lateral confinement layer of the active region is grown following the meltback, a buried heterostructure with fewer defects can be obtained, and furthermore, a striped structure can be formed. Even if fine irregularities are formed along the stripes during the formation of the mesa structure, these irregularities are eliminated by meltback, making it possible to create a waveguide with low loss, resulting in a low oscillation threshold and long life. It is possible to obtain a semiconductor laser of

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an outline of a buried heterostructure semiconductor laser, FIGS. 2 a to d are cross-sectional views showing the conventional manufacturing method in order of process, and FIGS. 3 a to d are cross-sectional views showing the manufacturing method of the present invention in order of process. FIG. 1...N-type 1nP substrate, 2,8...I
nGaASP layer, 3, 4... p-type 1nP layer, 5
...Insulating layer, 6,7...Metal electrode.

Claims (1)

[Claims] 1 On one main surface of an InP substrate of one conductivity type, InGa of one conductivity type or not doped with impurities
ASP layer, InP layer of the other conductivity type and InGaAS
A step of growing a P layer, a step of mesa etching until it reaches the main surface of the substrate to form both side surfaces along the propagation direction of the laser beam, and then melting it back from the surface and then adding the other layer to the surface. A method for manufacturing a semiconductor laser, comprising the step of growing a conductive type InP layer.