JPH07118571B2 - Semiconductor strained quantum well structure - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial application] The semiconductor quantum well structure is used for the active layer of semiconductor lasers and the light absorption layer of photodetectors and optical modulators, and has been proved to be effective in improving the characteristics of various devices. There is. Further, in recent years, research aiming at further improvement of characteristics by a strained quantum well structure in which a compressive strain or a tensile strain is added to a quantum well layer has been actively conducted, and the effect thereof has already been partially demonstrated. The present invention relates to such a semiconductor strained quantum well structure.

[0002]

2. Description of the Related Art Stress generated in a crystal when a crystal layer having a different lattice constant from that of a substrate crystal is laminated is called lattice strain.
When the quantum well layer in the quantum well structure has lattice strain,
The quantum well structure is called a strained quantum well structure.

FIG. 3 is a sectional view showing a conventional strained quantum well structure. This example is InGaAs / InGaAsP / In
P-type strained quantum well structure, for example, C.I. E. Zah
Electron, Lett. 27 (16), 141
5 (1991).

This strained quantum well structure is formed on the InP substrate 1,
InGaA having a lattice matching with the InP buffer layer 2 and the InP substrate 1 and a bandgap wavelength of 1.1 μm and a thickness of 20 nm.
and sP barrier layer 3 is obtained by laminating In _{0. 3} Ga _0.7 As strained quantum well layer 14, InP cap layer 6 having a thickness of 12.5nm with short lattice constant than InP substrate 1. The strained quantum well layer 14 has 1.6 in the direction parallel to the InP substrate 1.
% Tensile strain is added.

[0005]

In the strained quantum well structure, the crystal forming the quantum well layer has a different lattice constant from the substrate content, so that stress called lattice strain is generated inside the crystal. If the thickness of the quantum well layer exceeds a certain thickness called the critical thickness, lattice defects will occur in the crystal in an attempt to relax this lattice strain. For example, in the conventional strained quantum well structure shown in FIG. 3, when the layer thickness of the strained quantum well layer 14 is increased to 13 nm or more, which is the critical film thickness in the case of 1.6% strain, a lattice defect occurs, as shown in FIG. As described above, in the photoluminescence spectrum at a temperature of 77 K, light emission from a deep level due to crystal defects is observed in addition to band edge light emission. Then, such lattice defects significantly deteriorate the performance of the device.

It is an object of the present invention to provide a strained quantum well structure having a sufficiently large layer thickness per single quantum well and having few optical defects and excellent optical characteristics even in a region where the strain amount of the quantum well is large. is there.

[0007]

In the strained quantum well structure of the present invention, a single or a plurality of semiconductor layers having a lattice constant a ₂ are formed in a quantum well layer made of a semiconductor layer having a lattice constant a ₁ . ultra-thin film lattice distortion compensation layer is inserted and the lattice constant of the semiconductor substrate and a _0, a a ₁ <a ₀ ≦a ₂ Matawaa _1> a ₀ ≧ a _2. It is desirable that the ultrathin lattice distortion compensation layer has an extremely thin thickness such that electrons and holes can tunnel.

[0008]

In the present invention, when stacking strained quantum well structures,
The lattice constant of the semiconductor substrate a _0, when the lattice constant of the strained quantum well layer was set to _{a 1, a 1 <a 0 ≦a} 2 Matawaa _1> a ₀
Are inserted ≧ a ₂ lattice distortion compensation layer having a lattice constant a ₂ is in the strained quantum well layer. With such a structure of the present invention, the average strain amount per single strained quantum well layer is reduced, and thus the critical film thickness is increased, and the layer thickness per single quantum well that does not generate lattice defects is increased. There is.

[0009]

1 is a sectional view of a strained quantum well structure obtained according to an embodiment of the present invention. Here, InGaAs / I
An nGaAaP / InP strained quantum well structure will be described.

The structure of the present invention is based on InP on InP substrate 1.
InP having a layer thickness of 20 nm and a band gap wavelength of 1.1 μm, which has the same lattice constant a ₀ as the P buffer layer 2 and the InP substrate.
aAsP barrier layer 3, lattice constant a ₁ shorter than InP substrate
5 sets of strained quantum well layers 4 made of In _0.3 Ga _0.7 As layer having a thickness of 3 nm and having a lattice constant a longer than that of the InP substrate.
Consists ₂ from the lattice distortion compensation layer total thickness 17.4nm quantum well layer 10 consisting of a four sets and the 5, InP cap layer 6 made of InAs layer thickness 0.6nm with. And I
n _0.3 Ga _0.7 As strained quantum well layer 4 1.6% tensile distortions in, the lattice strain compensation layer 5 is applied 3.2% of the compressible strain respectively, on average in the whole quantum well layer 10 0.9
% Tensile strain is added, but since the critical film thickness at this time is 25 nm, no lattice defect occurs in the quantum well layer 10.

[0011]

FIG. 2 shows a photoluminescence spectrum of the strained quantum well structure obtained by the present invention at a temperature of 77K. In addition to band-edge emission with a narrow spectral line width, emission from deep levels due to crystal defects is not observed,
It can be seen that generation of crystal dislocation due to strain relaxation is suppressed. As described above, by using the structure of the present invention, it is possible to obtain a strained quantum well structure having a large film thickness per single quantum well and having excellent optical characteristics without lattice defects.

As an example, InGaAs / InG
Although the present invention has been described with reference to the single strain quantum well structure of aAsP / InP system, it is needless to say that the present invention can be applied to other material systems and also to a large strain quantum well structure.

[Brief description of drawings]

FIG. 1 is a sectional view of a strained quantum well structure according to an embodiment of the present invention.

FIG. 2 is a diagram showing an emission spectrum from the strained quantum well structure of the example of FIG.

FIG. 3 is a cross-sectional view of a strained quantum well structure obtained by implementing a conventional technique.

4 is a diagram showing an emission spectrum from the strained quantum well structure of FIG.

[Explanation of symbols]

1 InP substrate 2 InP buffer layer 3 InGaAsP barrier layer 4,14 In _0.3 Ga _0.7 As strained quantum well layer 5 lattice distortion compensation layer 6, 10 InP cap layer

Claims (2)

[Claims] _1. A semiconductor strained quantum well structure comprising a strained quantum well layer having a lattice constant a _{1 and} a barrier layer having a bandgap larger than that of the strained quantum well layer formed on a semiconductor substrate having a lattice constant a _0. In the strained quantum well layer, a single or a plurality of ultrathin film lattice strain compensation layers made of a semiconductor layer having a lattice constant a ₂ are inserted, and a ₁ <a ₀ ≦ a ₂ or a ₁
A semiconductor strained quantum well structure characterized in that> a ₀ ≧ a ₂ . 2. The semiconductor strained quantum well structure according to claim 1, wherein the ultrathin film lattice compensation layer is thin enough to tunnel electrons and holes.