JPH0582900A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent generation of a kink and fluctuations in a far field pattern when a high current is injected in an LD by eliminating 4 asymmetrical properties forbidden band width and a refractive index of the LD and reducing a spatial hole burning. CONSTITUTION:The method for manufacturing a semiconductor laser comprises the step of sequentially laminating a first conductivity type InP buffer layer 2, an InGaAsP buffer layer 3, an InGaAsP active layer 4, an anti-meltback layer 5 having the same composition and thickness as those of the layer 3, and a second conductivity type InP clad layer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor laser having a buried hetero structure.

[0002]

2. Description of the Related Art A semiconductor laser (hereinafter referred to as LD) having a buried hetero structure is mainly used for optical fiber communication. In particular, the 1.55 μm band silica optical fiber has low loss and is used for long-distance optical fiber communication.

Next, the structure of a 1.55 μm band LD manufactured by the conventional liquid phase epitaxial growth method will be described with reference to FIG. Figure 3
1 is an n-type InP substrate, 2 is an n-type InP buffer layer, 4
Is an InGaAsP active layer, 5 is an InGaAsP antimeltback layer, 6 is a p-type InP clad layer, and 7 is a p-type I.
nP current blocking layer, 8 is an n-type InP buried layer, 9 is a p-type InP buried layer, 10 is a p-type electrode, and 11 is an n-type electrode.

FIG. 3A shows a wafer in which a semiconductor growth layer having a double hetero structure including an active layer 4 serving as a light emitting region is formed on a substrate 1 in the first crystal growth. Where I
The nGaAsP anti-meltback layer 5 is laminated in order to prevent the meltback of the active layer 4, and the nGaAsP antimeltback layer 5 having a larger band gap and a smaller refractive index than InGaAsP of the active layer 4 is used.

In FIG. 3A, after the stripe-shaped convex portions are left on the wafer and the other portions are etched deeper than the active layer 4, the portions except the stripe-shaped convex portions are removed by the second crystal growth. The p-type InP current blocking layer 7, the n-type InP buried layer 8 and a p-type InP buried layer are sequentially grown on the entire surface.

[0006]

Next, the relationship between the forbidden band width and the refractive index with respect to the distance in the direction perpendicular to the joint surface in FIG. 3 is shown in FIG.
Shown in. FIG. 4A is a relationship diagram with the band gap, and FIG. 4A is a relationship diagram with the refractive index. Since the InGaAsP anti-meltback layer 5 is present in FIG. 3, the band gap and the refractive index are asymmetrical at the junction surface, as shown in FIGS. 4A and 4A.
In FIG. 3, when the current is increased and the light output is increased, the recombination of carriers is accelerated due to the strong stimulated emission in the central portion of the active layer 4, causing spatial hole burning in which the electron density is reduced. As a result, the position of the laser mode deviates from the peak position of the gain, which causes a kink in which the optical output does not increase even if the current is increased. Further, the gain distribution becomes asymmetric and the wavefront of the laser light is tilted with respect to the axis, which causes fluctuations in the far-field pattern.

The present invention eliminates the asymmetry between the forbidden band width and the refractive index of the LD, reduces the spatial hole burning,
It is intended to prevent the occurrence of kinks and the fluctuation of far-field images when a high current is injected into the LD.

[0008]

To achieve this object, according to the present invention, a first conductivity type InP buffer layer 2, an InGaAsP buffer layer 3, and an InGaAsP active layer 4 are formed on a first conductivity type InP substrate 1. , The InGaAsP buffer layer 3 having the same composition and the same film thickness, and the second conductivity type InP clad layer 6 are sequentially laminated.

[0009]

Next, the method of manufacturing the LD according to the present invention will be described with reference to FIG. Reference numeral 3 in FIG. 1 is an InGaAsP buffer layer, and the others are the same as those in FIG. InGaAsP
The buffer layer 3 has the same composition and the same film thickness as the anti-meltback layer 5. FIG. 1A shows the first crystal growth, in which the n-type InP buffer layer 2, I is formed on the n-type InP substrate 1.
nGaAsP buffer layer 3, InGaAsP active layer 4,
The InGaAsP anti-melt back layer 5 and the p-type InP clad layer 6 are sequentially laminated.

Next, by chemical etching, the stripe-shaped convex portions are left, and the other portions are etched deeper than the active layer 4. FIG. 1A shows the second crystal growth, in which a p-type InP current blocking layer 7, an n-type InP buried layer 8 and a p-type InP buried layer 9 are sequentially formed on the entire surface except the stripe-shaped convex portion. And finally, the p-type electrode 10 and the n-type electrode 11
To form.

Next, FIG. 2 shows the relationship between the forbidden band width and the refractive index with respect to the distance in the direction perpendicular to the joint surface in FIG. FIG. 2A is a relationship diagram with the band gap, and FIG. 2A is a relationship diagram with the refractive index. The composition of the active layer 4 is I when the oscillation wavelength is 1.55 μm.
In _0.65 Ga _0.35 As _0.79 for lattice matching with nP
P _0.21 , the band gap is 0.8 eV, and the refractive index is 3.54. The thickness of the active layer 4 is about 0.1 μm. InG
The composition of the aAsP buffer layer 3 and the InGaAsP anti-meltback layer 5 is In _0.76 Ga _0.24 As _0.55 P _0.45 and the refractive index is 3.51. The film thickness is sufficiently thinner than that of the active layer 4.
It is about 03 μm. On the other hand, InP has a band gap of 1.35 eV,
Since the refractive index is 3.40, the bandgap distribution and the refractive index distribution shown in FIG. 2 are obtained.

[0012]

According to the present invention, InGaA having the same composition and the same film thickness as the InGaAsP anti-melt back layer 5 is formed.
Since the sP buffer layer 3 is stacked below the active layer 4,
The distribution of the forbidden band in the direction perpendicular to the junction surface and the refractive index distribution are symmetrical, spatial hole burning is reduced even at the time of high current injection, and there is no kink or fluctuation in the far-field pattern.
D can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for manufacturing an LD according to the present invention.

FIG. 2 is a relationship diagram of a forbidden band width and a refractive index with respect to a distance in a direction perpendicular to a joint surface of FIG.

FIG. 3 is an explanatory diagram of a method for manufacturing an LD according to a conventional technique.

FIG. 4 is a relationship diagram of a forbidden band width and a refractive index with respect to a distance in a direction perpendicular to a joint surface of FIG.

[Explanation of symbols]

 1 n-type InP substrate 2 n-type InP buffer layer 3 InGaAsP buffer layer 4 InGaAsP active layer 5 InGaAsP anti-melt back layer 6 p-type InP clad layer

Claims (1)

[Claims] 1. A first conductivity type InP substrate (1), a first conductivity type InP buffer layer (2), an InGaAsP buffer layer (3), an InGaAsP active layer (4), and InGaAs.
Manufacturing of a semiconductor laser characterized by comprising a step of sequentially laminating an anti-meltback layer (5) having the same composition and thickness as the P buffer layer (3) and a second conductivity type InP clad layer (6). Method.