JPH05343738A - Manufacture of optical semiconductor device - Google Patents

Abstract

PURPOSE:To deposit a thick distortion superlattice layer having a low non-light irradiating level and dislocation, a large distortion in deposition of the superlattice layer having a multiple quantum well structure. CONSTITUTION:The method for manufacturing an optical semiconductor device comprises the steps of sequentially depositing an optical waveguide layer 3 formed of a compound semiconductor single crystal, a distortion superlattice layer 4 and a light confining layer 5 on a substrate in such a manner that the layer 5 is deposited at a lower temperature than a depositing temperature of the layer 4.

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 an optical semiconductor device having a strained superlattice layer forming a multiple quantum well structure.

A semiconductor laser applied to large-capacity optical communication is required to have high speed, low chirp, and a narrow spectrum width. Recently, multi-quantum well lasers have been used to increase the spectral width by utilizing the change of the density of states function based on the quantum size effect, the increase of the differential gain due to the increase of the dipole moment, and the reduction of the line width increase coefficient (α parameter). Improvements have been made.

Further, in order to improve the characteristics of the multiple quantum well laser, a strained quantum well laser has been developed which introduces strain to reduce the effective mass of holes and operates even when the carrier density is low.

In order to bring out the characteristics of an optical semiconductor device using such a strained superlattice, for example, a strained quantum well laser, the strained superlattice layer serving as an active layer has little light absorption and a sufficient strain is introduced. Must have a sufficient thickness to adjust the characteristic wavelength of PL (photoluminescence) emission which varies due to

Therefore, light absorption is small, distortion is large,
What is needed is a method for manufacturing an optical semiconductor device in which a strained superlattice layer made of a thick compound semiconductor is epitaxially deposited.

[0006]

2. Description of the Related Art In order to deposit a strained superlattice layer made of a compound semiconductor in the fabrication of a conventional optical semiconductor device, an optical waveguide layer, a strained superlattice layer, and an optical confinement layer are sequentially formed on a semiconductor substrate at the same temperature. It was deposited epitaxially at.

However, it is necessary to raise the deposition temperature in order to prevent generation of non-emission levels due to vacancies in the strained superlattice layer, contamination of impurities, and disorder of the crystal lattice. On the other hand, when the growth temperature is high, dislocations are introduced into the strained superlattice layer and the strain in the strained superlattice layer is partially relaxed. As a result, the PL emission spectrum of the strained superlattice layer splits, degrading the characteristics of the optical semiconductor device.

Such dislocations are introduced easily and in large quantities as the strain of the strained superlattice layer increases and the strained superlattice layer thickens. Therefore, according to the conventional method, the non-emission level is small, and at the same time, the strained superlattice layer having large strain cannot be deposited thickly.

[0009]

As described above, in the conventional method for manufacturing an optical semiconductor device in which all layers of the optical waveguide layer, the strained superlattice layer, and the optical confinement layer are deposited at the same temperature, the non-luminous Since both generation of levels and introduction of dislocations cannot be prevented at the same time, there is a problem in that there are few non-radiative levels and dislocations, and it is not possible to deposit a strained superlattice layer having large strain thickly.

According to the present invention, a strained superlattice layer having a small number of non-emission levels is deposited at a high temperature, and then an optical confinement layer deposited thereon is grown at a low temperature to prevent dislocation introduction into the strained superlattice layer. By doing so, it is an object of the present invention to provide a method for manufacturing an optical semiconductor device capable of depositing a thick strained superlattice layer having a large number of non-emission levels and dislocations and a large strain.

[0011]

FIG. 1 is a sectional view of an embodiment of the present invention. FIG. 1 (a) is a compound semiconductor layer structure deposited on a substrate, and FIG. 1 (b) is a partially enlarged view thereof. Which represents the multiple quantum well structure of the strained superlattice layer.

In order to solve the above problems, referring to FIG. 1, the first structure of the present invention is to provide an optical waveguide layer 3, a strained superlattice layer 4, and an optical closing layer made of a compound semiconductor single crystal on a substrate. A step of sequentially depositing the confinement layer 5 and the optical confinement layer 5 is deposited at a temperature lower than the deposition temperature of the strained superlattice layer 4, and the second configuration comprises In the method of manufacturing an optical semiconductor device having the first configuration, a step of depositing InGaAsP to form the optical waveguide layer 3, and 600 ° C. to 700 ° C.
A step of alternately stacking quantum well layers 4a made of InGaAs and barrier layers 4b made of InGaAsP at a deposition temperature of ℃ to form the strained superlattice layer 4; And a step of forming the light confining layer 5.

[0013]

FIG. 2 is a diagram for explaining the principle of the present invention, showing the dependency of the trap concentration of the strained superlattice layer on the deposition temperature.

The trap concentration in FIG. 2 is MOCVD.
Method (organic metal chemical vapor deposition method)
Quantum well layer made of nGaAs and 10 nm thick InGa
The strained superlattice layer in which five barrier layers made of AsP are alternately laminated is measured by the DLTS method.

The trap concentration of the strained superlattice layer is maintained at a constant value at a deposition temperature of 600 ° C. or higher, but sharply increases at a deposition temperature of 570 ° C. or lower due to an increase in non-emission level. That is, in the strained superlattice layer, the trap concentration increases at the deposition temperature below the critical temperature corresponding to the type,
There is a critical deposition temperature at which trap concentrations are lower at higher deposition temperatures.

In the structure of the present invention, referring to FIG. 1, the strained superlattice layer 4 is, for example, 60
The optical confinement layer 5 deposited at 0 ° C. or higher and then deposited is deposited at a low temperature, for example, 570 ° C. or lower.

In such a structure, the strained superlattice layer 4 deposited at a high temperature does not include a non-emission level, while the subsequent deposited layers are deposited at a low temperature, the dislocation density of the strained superlattice layer 4 is small. is there.

That is, dislocations are introduced by generating stress by epitaxially growing optical confinement layers having different lattice constants on the strained superlattice layer. Therefore, in the structure of the present invention in which the temperature during the growth of the light confinement layer is low, the activation energy for introducing and propagating dislocations in the crystal is large, and thus the generation of dislocations is suppressed.

Therefore, both the non-emission level density and the dislocation density in the strained superlattice layer are small, and the strain of the strained superlattice layer can be large and thick. It is needless to say that the present invention is applied to the strained superlattice subject to both compressive and tensile stresses.

[0020]

EXAMPLES The details of the present invention will be described below with reference to examples. First, the n-type InP substrate 1 having a plane orientation (100) is
Place in OCVD equipment and hold at 615 ° C.

Then, trimethylindium (TMI
n) and PH ₃ are used as source gases, and 2000 nm thick n-type InP is deposited as the buffer layer 2. Then, as the optical waveguide layer 3, TM-type n-type InGaAsP having a thickness of 150 nm is used.
In, triethylgallium (TEGa), AsH ₃ , and PH ₃ are deposited as source gases.

Next, InGaAsP having a thickness of 1.8 nm is used as a quantum well layer, and InGaAsP having a thickness of 10 nm is used as a barrier layer, and five layers are alternately stacked and deposited to form a strained superlattice layer. Then, the inflow of the compound gas of the group III element is stopped to interrupt the deposition, the substrate temperature is lowered, and the temperature is maintained at 570 ° C.

Again, the compound gas of the group III element is flowed in to p-type InGaAsP having a thickness of 150 nm into the optical confinement layer 5.
To be deposited as. Next, InP having a thickness of 450 nm is deposited as the contact layer 6 to manufacture a compound semiconductor crystal used in an optical semiconductor device.

FIG. 3 is an explanatory view of the effects of the present invention, showing the PL emission characteristics of the compound semiconductors manufactured according to the examples of the present invention. FIG. 3 (a) is a PL emission spectrum at 4.2K, where A is the compound semiconductor manufactured by this example, and a is the compound semiconductor manufactured by the conventional method with a deposition temperature of 615 ° C. It represents the thing.

The conventional examples being compared have the same growth conditions and the same semiconductor type and structure except for the deposition temperature. Further, Kr laser light is used as excitation light, and the sample is immersed in liquid helium for measurement.

Those manufactured by the conventional method show that the emission spectrum was split, dislocations were introduced into the strained superlattice layer, and stress relaxation occurred in a part of the strained superlattice layer. On the other hand, according to the present example, the splitting of the emission spectrum is slightly observed, and it is clearly shown that dislocations are hard to occur and propagate in the strained superlattice layer.

Next, FIG. 3 (b) is a PL emission spectrum at room temperature. In the figure, A is the compound semiconductor manufactured by this example, and a is a conventional method in which the deposition temperature is 570.degree. It represents a compound semiconductor.

The conventional examples to be compared have the same growth condition and the same kind and structure of semiconductor except the deposition temperature. From FIG. 3B, the PL emission intensity of the compound semiconductor according to this example is about twice that of the conventional one. This difference in emission intensity is caused because the conventional one contains a non-emission level, and it is clarified that the non-emission level of the compound semiconductor according to the present invention is small.

As described above, the strained superlattice layer according to the present invention has few non-emission levels and less stress relaxation due to dislocations. Therefore, the strain can be made larger than before, and the strained superlattice layer can be thickened.

[0030]

According to the present invention, the strained superlattice layer is deposited at a high temperature, and then the light confinement layer is grown on the strained superlattice layer at a low temperature to prevent the generation of the non-emission level in the strained superlattice layer. In addition, since it is possible to prevent the introduction and propagation of dislocations, it is possible to deposit a thick strained superlattice layer having a large amount of strain, with a small number of non-emission levels and dislocations. It is possible to provide a good manufacturing method of an optical semiconductor device, which largely contributes to performance improvement of optical application equipment.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the principle of the present invention.

FIG. 3 is an explanatory diagram of the effect of the present invention.

[Explanation of symbols]

 1 substrate 2 buffer layer 3 optical waveguide layer 4 strained superlattice layer 4a quantum well layer 4b barrier layer 5 optical confinement layer 6 contact layer

Claims (2)

[Claims] 1. A step of sequentially depositing an optical waveguide layer (3) made of a compound semiconductor single crystal, a strained superlattice layer (4), and an optical confinement layer (5) on a substrate. A method for manufacturing an optical semiconductor device, comprising depositing a confinement layer (5) at a temperature lower than a deposition temperature of the strained superlattice layer (4). 2. The method for manufacturing an optical semiconductor device according to claim 1, wherein the step of depositing InGaAsP to form the optical waveguide layer (3), and the quantum well made of InGaAs at a deposition temperature of 600 ° C. to 700 ° C. Layer (4a) and barrier layer (4b) made of InGaAsP are alternately laminated to form the strained superlattice layer (4), and InGaAsP is deposited at a deposition temperature of less than 600 ° C. to confine the light. And a step of forming a layer (5).