JPH07147454A - Semiconductor element - Google Patents

Abstract

PURPOSE:To improve characteristic such as realization of a low threshold value of a semiconductor element by making the strain amount of a strain quantum well uniform. CONSTITUTION:The lattice constant difference of strain quantum wells 4, 5, 6, 7, 8 constituting a strain multiquantum well active layer 10 to a strain-free n-InP substrate 1 is made larger in the strain quantum wells 5, 6, 7 positioned inside compared to the strain quantum wells 4, 8 which are closest to a p-InP clad layer 12. Since relaxation of the strain of the strain quantum wells 4, 5, 6, 7, 8 positioned inside a multiple strain quantum well can be thereby ensured, the strain amount can be maximized in a range of a critical film thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a multiple strain quantum well structure and other semiconductor devices.

[0002]

2. Description of the Related Art Conventionally, by forming a quantum well structure in an active layer of a semiconductor laser, many characteristics such as low threshold, narrow spectral line width, and high output have been improved as compared with a bulk active layer. . Recently, it is theoretically possible to further improve these characteristics by distorting the quantum well by using a material different from the lattice constant of the substrate for the quantum well, that is, by introducing a strained quantum well. Is also shown experimentally. As an example of a quantum well laser that has characteristics of a low threshold and a narrow spectral line width due to compressive strain, an electronic letter (Electron. Lett.) 2
7, 1628 (1991).

[0003]

The above characteristic improvement is caused by the change in the band structure of the quantum well layer due to strain. Specifically, strain stress causes an increase in separation of heavy holes and light holes in the valence band of a semiconductor crystal forming a quantum well, and a change in band structure such as a decrease in hole effective mass. It is thought that this was because the gain enhancement, Auger recombination, and loss reduction due to absorption between valence bands were obtained.

However, in order to obtain such a distortion effect,
A large strain amount of 1% or more is required. Since the critical film thickness decreases as the amount of strain increases, the amount of strain is limited by the controllability of crystal growth and the quantum well width constraint practical in terms of device design. In addition, the multi-strained quantum well has a lattice constant difference of f
In the case of a strained superlattice in which two types of thin films having film thicknesses h ₁ and h ₂ , rigidity factors G ₁ and G ₂ and lattice constants a ₁ and a ₂ are alternately laminated, Lattice constant a in the direction parallel to the interface of
Is given by Equations 1 and 2, and the lattice constant a of the strained superlattice is
Take an intermediate value between a ₁ and a ₂ .

[0005]

[Equation 1]

[0006]

[Equation 2]

Accordingly, a lattice constant of a ₁ barrier layer, multiple strained quantum well lattice constant is made from the well layer of a ₂ is, in interposed at the substrate and the cladding layer of identical lattice constants a ₁ and a barrier layer , strain of the well layer, outside of the well layer in contact with the substrate or the cladding _{layer, | a 2 -a 1 | /} a 1 a but, at the center of the multiple strained quantum well, | a ₂ -a | / a Becomes smaller than the outer well layer. That is, the strain amount of the entire multi-strained quantum well becomes smaller than the strain amount | a ₂ −a ₁ | / a ₁ predicted from the lattice constant difference due to the relaxation of the strain amount of the quantum well layer located in the central portion. Moreover, the strain amount of each well layer is also non-uniform. Therefore, there is a problem that not only the emission spectrum width is widened but also the expected effect of distortion cannot be obtained sufficiently.

An object of the present invention is to increase the strain amount of the multi-strain quantum well while keeping the critical film thickness constant by making each strain amount of the multi-strain quantum well uniform. It is intended to improve the characteristics of the semiconductor laser provided, a semiconductor device such as a light receiving element, and the like.

[0009]

In order to solve the above-mentioned problems, the present invention makes the well layer farther from the substrate larger than the well layer closest to the substrate with respect to the difference in lattice constant from the substrate. By doing so, the multi-strained quantum well structure is formed so that the strain amount of each well layer becomes constant. In addition, as described above, when the lattice constant of the clad layer is the same as that of the substrate, the lattice constant difference between the substrate and the well layer closest to the clad layer is larger than that of the well layer closest to the clad layer. Take big. That is, by making the central well layer of the multi-strained quantum well have a larger lattice constant difference from the substrate than the outer well layer, the strain amount of each well layer is made uniform.

As described above, the lattice constant of each well layer is changed by changing the composition of a mixed crystal semiconductor such as InGaAsP, but at this time, the emission transition wavelength of each well layer becomes equal. The composition.

[0011]

According to the present invention, since the amount of strain in each well layer of the multi-strained quantum well is uniform, the center of the well-like multi-strained quantum well, which is composed of well layers having a constant lattice constant difference from the substrate, is used. There is no reduction in the amount of strain in the quantum wells of the part. Therefore, it is possible to increase the strain amount of the entire multi-strain quantum well as compared with the related art.

[0012]

EXAMPLE FIG. 1 shows an oscillation wavelength of 1. Example of the present invention.
It is a sectional view of a 3 μm band semiconductor laser. The feature of the present invention resides in the structure of the multi-strained quantum well active layer 10 formed on the n-InP substrate 1. The multi-strained quantum well active layer 10 is
The first InGaAsP closest to the n-InP substrate 1
Five compressive strain quantum wells (each having a layer thickness of 6 nm) from the strain quantum well 4 to the fifth InGaAsP strain quantum well 8 closest to the p-InP cladding layer 12 and a layer thickness 10
nm, composition wavelength 1.1 μm InGaAsP barrier layer 9
However, it has a structure in which they are alternately laminated. InG
The aAsP barrier layer 9 is lattice-matched with the n-InP substrate 1.

Since the five strained quantum wells have compressive strain, the lattice constant is larger than that of the n-InP substrate 1, and the lattice constant difference is 1 in the first and fifth strained quantum wells 4 and 8. .
5%, the second and fourth strained quantum wells 5 and 7 are 1.8%,
The third strain quantum well 6 is set to 2.1%. Thus, the strained quantum wells 5 and 6 and 7 located in the central portion of the active layer are
The n-InP substrate 1 or the p-InP clad layer 1
The strain amount of each strained quantum well is made uniform to about 1.5% by making the lattice constant difference larger than that of the strained quantum wells 4 and 8 which are close to 2.

When the oscillation threshold current density of the semiconductor laser having the above characteristics is measured, it is reduced by about 30% as compared with the semiconductor laser having five strained quantum wells in which the lattice constant differences are all 1.5%. Therefore, the effectiveness of the present invention was confirmed.

In this embodiment, the lattice constant difference distribution of each strained quantum well gradually increases toward the strained quantum well located near the center of the active layer 10, as shown in FIG. However, as shown in FIG. 3, the strained quantum wells 5, 6 and 7 located in the central portion of the active layer may be constant. In addition, in each of the examples, the composition is set so that the emission transition wavelength of each strained quantum well is 1.3 μm.

Although an example of an InP-based multiple quantum well semiconductor laser having a compressive strain has been described above, the present invention can be applied to the case of tensile strain and also to a semiconductor element having a different material system such as GaAs. Is possible.

[0017]

According to the present invention, the strain amount of the multi-strained quantum well can be maximized within the range of the critical film thickness of each quantum well. Therefore, the characteristics of the semiconductor element are improved by utilizing the effect of strain, particularly, the threshold value of the semiconductor laser is reduced, the spectral line width is narrowed,
It has a great effect on high output.

[Brief description of drawings]

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

FIG. 2 is a graph showing an array of lattice constants of each layer forming a quantum well in an element of an example of the present invention.

FIG. 3 is a graph showing an array of lattice constants of respective layers forming a quantum well in a device of another example of the present invention.

[Explanation of symbols]

1 ... n-InP substrate, 2 ... n-InP buffer layer, 3 ...
n-InGaAsP guide layer, 4 ... First InGaAs
P ... 9 ... InGaAsP barrier layer, 10 ... Multi-strained quantum well active layer, 11 ... p-InGaAsP guide layer,
12 ... p-InP clad layer, 13 ... n electrode, 14 ... p
electrode.

Claims (2)

[Claims] 1. A semiconductor device having a multi-strained quantum well structure in which a plurality of strained quantum wells and barrier layers are alternately stacked on a semiconductor substrate, and having a clad layer stacked on the multiple quantum well structure. , The lattice constant difference with the semiconductor substrate in the strain-free state of the strained quantum well, the semiconductor substrate, or, as compared to the quantum well closest to the cladding layer,
A semiconductor element characterized in that the quantum well located farther from the semiconductor substrate or the cladding layer is larger. 2. The semiconductor device according to claim 1, wherein the emission transition wavelengths in the strained quantum wells are all substantially the same.