JPS61294877A - Semiconductor device - Google Patents

Abstract

PURPOSE:To grow and form a high quality semiconductor crystal, by forming a semiconductor layer, which constitutes a second semiconductor that is contacted with a third semiconductor, with a semiconductor material, whose lattice constant is smaller than the lattice constant of the third semiconductor. CONSTITUTION:A semiconductor device is formed by sequentially laminating a buffer layer 12 and a gallium arsenide crystal 13 on a silicon substrate 11 having a surface orientation of [100]. The buffer layer 13 comprises 10 SiGe mixed crystal layers, with their composition ratios being increased stepwise by every 0.1. In this semiconductor device, it is necessary that the thickness of each SiGe layer constituting the buffer layer 12 is set at a value larger than the critical thickness, which can be alleviated in dislocation newly caused by the lattice misalignment between the layers. In this case, the thickness is all set at about 0.2mum. Thus problems such as cracking and peeling can be avoided, and the device having excellent crystalline property is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor device using a semiconductor crystal formed on a different substrate with a buffer layer interposed therebetween.

[Technical background of the invention and its problems]

Hereinafter, a gallium arsenide solar cell formed on a silicon substrate with a germanium buffer layer interposed therebetween will be described as an example.

FIG.
International pvSEC-1, Kobe 2 Japan, PP
837-840.19841(”Developame
nt of Light-Weight Th1n G
aAs5olar Ce1ls on St 5ubs
trates:Technical Digest o
f the International PV
SEC-1, kobe.

Japan, pp 837-840.1984") is a cross-sectional view showing the main components of a gallium arsenide solar cell formed on a silicon substrate with a germanium buffer layer interposed therebetween, and in the figure, 1 is a silicon substrate. , 2 is a germanium buffer layer formed on a silicon substrate, and 3 is a gallium arsenide crystal layer formed on the dalmanium buffer layer.

The lattice constants of silicon, germanium, and gallium arsenide crystals at room temperature are each 5.431X.

5.658X, 5.654X, and the lattice mismatch between the silicon crystal and the gallium blank crystal is as large as about 4%, while the lattice mismatch between the germanium crystal and the gallium blank crystal is as small as 0.04% or less. . For this reason, when a gallium arsenide crystal is grown directly on a silicon substrate, there are many electrically and optically active crystals represented by dislocations within the grown gallium arsenide crystal due to the large lattice mismatch. Defects are introduced, and devices formed using such low-grade gallium amorphous crystals are unsuitable for practical use in terms of performance. On the other hand, if a dalmanium crystal, which has a small lattice mismatch with the gallium non-crystal, is inserted as a buffer layer between the silicon crystal and the gallium non-crystal, most of the crystals caused by the lattice mismatch with the silicon crystal can be removed. Defects can be absorbed into the dalmanium buffer layer, so
On top of this, high-grade gallium green crystals can be grown.

However, the lattice constant of gallium uncrystallized is slightly smaller than that of dalmanium crystal;
Furthermore, the coefficient of linear expansion of silicon crystal (approximately 2.3
10-'℃-1) is the value of gallium uncrystallized (approximately 5.8
1) at x 10-' and the value of germanium crystals (approximately 5.
7 x 10"-6℃-1),
When the crystal growth temperature is returned to room temperature, a large tensile stress is applied to the gallium uncrystallized material. For this reason, the lattice constant of the obtained gallium uncrystallized material shows a value υ larger than the normal value, and the physical property constants represented by the energy band gag differ from the original values. Also,
When the thickness of the gallium uncrystallized film is increased to more than about 3 μm, which is necessary for forming devices such as solar cells, a breakdown phenomenon occurs, and problems such as the gallium uncrystallized cracking or peeling from the germanium buffer layer occur.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a high-performance semiconductor device using the same by growing high-quality semiconductor crystals on a different type of semiconductor substrate. There is a particular thing.

[Summary of the invention]

In order to achieve the above object, the present inventors conducted various experiments and found that when a semiconductor crystal is grown and formed on a different type of semiconductor substrate with a buffer layer interposed therebetween, the buffer layer is formed on the surface of a semiconductor lattice. If the semiconductor material is formed with a semiconductor material having a value smaller than the constant, compressive stress will always act on the semiconductor formed on the buffer layer, and problems such as cracking and peeling will not occur, and the buffer layer and the It has been found that by properly achieving lattice matching with the semiconductor to be formed, the physical constants of the semiconductor can be brought closer to the values inherent to the semiconductor.

To this end, on the surface of the first semiconductor serving as the substrate,
In a semiconductor device having a structure in which at least a second semiconductor composed of one or more semiconductor layers serving as a buffer layer and a third semiconductor of a different type from the first semiconductor are sequentially stacked, Among the semiconductor layers constituting the second semiconductor, which serves as a buffer layer of the third semiconductor, at least the semiconductor layer constituting the second semiconductor in contact with the third semiconductor has a lattice constant equal to that of the third semiconductor. A semiconductor device characterized in that it is formed of a semiconductor material having a lattice constant smaller than the lattice constant of a semiconductor, further comprising a silicon crystal as the first semiconductor and a silicon-kemanium mixed crystal layer or silicon as the second semiconductor. A silicon-germanium mixed crystal that constitutes the second semiconductor that is composed of a darmanium mixed crystal layer and a germanium crystal layer and that is in contact with gallium arsenide that is the third semiconductor when the third semiconductor is gallium arsenide. We have proposed a semiconductor device characterized in that the value of X is set to 0.98 or less when the composition is expressed as St and xGeX.

[Embodiments of the invention]

In the following, a semiconductor device in which the substrate is a silicon crystal, the buffer layer is formed of a silicon germanium mixed crystal or a silicon germanium mixed crystal and a germanium crystal, and a gallium non-crystal is formed on the surface thereof will be described as an example. An example will be explained. Note that hereinafter, the composition of the silicon germanium mixed crystal will be expressed as Sl, -xG@technique. Further, crystal growth was performed using a molecular beam epitaxial apparatus.

In the first embodiment of the present invention, Si with a thickness of about 1 μm and a composition ratio X of 0.95 is formed on a silicon substrate with a plane orientation of [100].
This is a semiconductor device formed by sequentially stacking a buffer layer made of 1□GeX mixed crystal and gallium amorphous crystal.

Since the semiconductor device according to this embodiment has a cross section similar to that of the semiconductor device shown in FIG. 3, a description thereof will be omitted here.

In this example, the thickness of the Sl, -XGeX mixed crystal layer must be set to a value greater than or equal to the critical thickness at which the lattice mismatch with the silicon substrate can be alleviated by newly generated dislocations.
Here, it was set to about 1 μm. Note that if this thickness is less than the critical thickness, the lattice mismatch will not be sufficiently alleviated.

In addition, 81. -Ge
Based on the equation (1) expressing the lattice constant of the G@technical mixed crystal, the value of X must be 0.98 or less. In this example, a 511-xGex mixed crystal with X of 0.95 was used.

d(x)=5.431+0.227X(i), -(
1) Here, d(x) represents the lattice constant of the 511-EGCx mixed crystal.

On the surface of the buffer layer formed under the conditions described above, 1μ
We tried growing gallium amorphous crystals with a thickness in the range from m to 10 μm, but no problems such as cracking or peeling occurred.

Further, the lattice constant measured by X-ray diffraction showed a value extremely close to the above-mentioned characteristic value of gallium arsenide.

Next, FIG. 1 shows a second embodiment of the present invention, and the surface orientation (
100) on a silicon substrate 11 with a composition ratio X of 0.05.
This semiconductor device is formed by sequentially stacking a buffer layer 12 made of 10 layers of Sl and -XGeX mixed crystal layers and a gallium uncrystal 13, which are formed in steps of 0.1 from 0.95 to 0.95.

Also in this embodiment, each of the 511-
It is necessary to set the XGex layer to a thickness greater than a critical thickness at which the lattice mismatch between each layer can be alleviated by newly generated dislocations, and here the thicknesses were all set to about 0.2 μm.

Note that if this thickness is less than the critical thickness, the lattice mismatch will not be sufficiently alleviated. Also in this example,
Gallium amorphous crystals 13 having a thickness in the range of 1 μm to 10 μm were grown on the surface of the buffer layer 120, but similar to the first example described above, no problems such as cracking or peeling occurred.

Next, in FIG. 2, the buffer layer 22 is made of dalmanium crystal and Si
1 +, c1! The third compound of the present invention formed with X mixed crystal
This is an example of a silicon substrate 11 with a plane orientation (1003).
On top, there is an r-rumanium crystal layer with a thickness of about 1 μm and an Si 1 + XG layer with a composition ratio X of 0.95 and a thickness of about 0.2 μm.
This is a semiconductor device formed by sequentially stacking a buffer layer 22 made of an aX mixed crystal layer and gallium amorphous crystal 13.

In this example as well, we tried to grow uncrystallized gallium 13 on the surface of the buffer layer 22 with a thickness ranging from 1 μm to 10 μm, but as in the first example described above, cracks, peeling, etc. No problems occurred.

Although the above embodiments have only described the case where a silicon germanium mixed crystal is used as the buffer layer, other semiconductor materials whose lattice constants can be controlled by changing the composition ratio, such as compound mixed crystals such as gallium arsenide phosphorus, etc. It goes without saying that similar effects can be expected by using other materials.

〔Effect of the invention〕

As explained above, in the semiconductor device according to the present invention, since compressive stress is always applied to the semiconductor crystal formed on a different substrate, problems such as cracking and peeling can be avoided even when the semiconductor crystal is formed thickly, and the crystallinity is It has the great feature of providing excellent results.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor device showing a second embodiment of the invention, and FIG. 2 is a sectional view of a semiconductor device showing a third embodiment of the invention. FIG. 3 is a sectional view showing the main components of a conventionally proposed gallium arsenide solar cell formed on a silicon substrate with a germanium buffer layer interposed therebetween. 11... Silicon substrate, 12.22... Buffer layer, 1
3...Gallium arsenide crystal. Applicant's agent Patent attorney Takehiko Suzue 1st v.! J Figure 2 Figure 3

Claims (2)

[Claims] (1) On the surface of the first semiconductor serving as a substrate, a second semiconductor composed of at least one or more semiconductor layers serving as a buffer layer, and a third semiconductor which is different from the first semiconductor. In a semiconductor device having a structure in which semiconductors are sequentially stacked, among the semiconductor layers constituting the second semiconductor, which serves as a buffer layer of the third semiconductor, at least the second semiconductor layer in contact with the third semiconductor A semiconductor device characterized in that a semiconductor layer constituting the semiconductor is formed of a semiconductor material whose lattice constant has a smaller value than the lattice constant of the third semiconductor. (2) The first semiconductor is a silicon crystal, the second semiconductor is composed of a silicon germanium mixed crystal layer or a silicon germanium mixed crystal layer and a germanium crystal layer, and the third semiconductor is composed of a silicon germanium mixed crystal layer or a silicon germanium mixed crystal layer and a germanium crystal layer.
When the semiconductor is gallium arsenide, the composition of the silicon germanium mixed crystal constituting the second semiconductor in contact with the third semiconductor gallium arsenide is Si_1_-_
2. The semiconductor device according to claim 1, wherein the value of x is set to 0.98 or less when expressed as xGe_x.