JPH05267703A - Semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a semiconductor device, in particular, a solar cell, which is capable of efficiently absorbing light in all wavelength regions of short wavelength to long wavelength of sunlight. .. In a device for providing a compound semiconductor layer having a hetero structure on a substrate 21, absorbing sunlight by the compound semiconductor layer, and photoelectrically converting the absorbed sunlight, light energy of the sunlight having a short wavelength is obtained. A wide-energy-gap superlattice layer 22 capable of absorbing light, a narrow-energy-gap superlattice layer 23 capable of absorbing long-wavelength light energy of the sunlight, or a substrate
It is formed by sandwiching 21 to allow absorption of light energy in the entire wavelength region of the sunlight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a solar cell capable of absorbing light energy of sunlight with high efficiency and performing photoelectric conversion.

[0002]

2. Description of the Related Art Conventionally, various solar cells have been proposed, but as shown in FIGS. 5 (a) and 5 (b), a p-type cadmium sulfide (compound semiconductor having a large energy gap Eg ₁ CdS) layer 1 and cadmium telluride (CdTe) layer 2 having a small energy gap Eg ₂ are laminated in a hetero structure,
An electrode 3A made of a stripe-shaped gold-germanium alloy is provided on the CdS layer 1, and gold is formed on the entire surface on the CdTe layer 2.
There is a solar cell including a heterojunction photovoltaic semiconductor device provided with an electrode 3B made of a germanium alloy. Here, 11 in FIG. 5 (b) indicates the energy level at the bottom of the conduction band, and 12 indicates the energy level at the top of the valence band.

Separately from this, in FIGS. 6 (a) and 6 (b),
As shown, energy gap Eg ₁Is 2.0 eV
Amorphous Si nitride layer (SiN:
H) 4, energy gap Eg₂Adds hydrogen at 1.7 eV
, An amorphous Si layer (Si: H) 5 with a pn junction, energy
Lugie Gap Eg₃Is 1.4eV, hydrogen is added, pn contact
Amorphous germanium Si layer (SiGe: H) 6
Tandem solar with electrodes 3A and 3B stacked in sequence.
There is a battery. Here, 11 in Fig. 6 (b) is the energy at the bottom of the conduction band.
Level, where 12 is the energy level above the valence band.
Indicates the

The above-described conventional solar cell combines a material with a wide energy gap and a material with a narrow energy gap to absorb sunlight as efficiently as possible and perform photoelectric conversion. The semiconductor device is formed by using two kinds of materials having different energy gaps, and the latter tandem type semiconductor device uses only three kinds of materials having different energy gaps, and all of them are light energy of sunlight. The conversion efficiency of converting electricity into electric energy is around 20%, and the conversion efficiency is low, and a solar cell having even higher conversion efficiency is desired.

[0005]

[Problems to be Solved by the Invention] The wavelength of sunlight is 0.3 μ.
The wavelength range is widely distributed from sunlight with a short wavelength of m to light with a long wavelength of 2.4 μm, and semiconductors that can efficiently absorb light in these wide wavelengths and can perform photoelectric conversion efficiently. A device is desired.

The present invention has been made in view of the above matters, and an object of the present invention is to provide a semiconductor device capable of efficiently absorbing all sunlight having a wide range of wavelengths and efficiently performing photoelectric conversion.

[0007]

The semiconductor device of the present invention comprises:
In a device for providing a compound semiconductor layer having a heterostructure on a substrate, absorbing sunlight by the compound semiconductor layer, and photoelectrically converting the absorbed sunlight, a short wavelength of sunlight is obtained. A wide energy gap superlattice layer capable of absorbing the light energy of, a narrow energy gap superlattice layer capable of absorbing the light energy of the long wavelength of the sunlight are laminated, or provided by sandwiching the substrate, and the whole wavelength range of the sunlight is provided. It is characterized in that it can absorb the light energy of.

Further, as described in claim 2, it is formed by changing the thickness of the barrier layer and the well layer of the wide energy gap superlattice layer and the narrow energy gap superlattice layer stepwise or continuously. It is characterized in that the energy gap of the superlattice layer is varied.

[0009]

[Operation] Sunlight is distributed from short-wavelength light with a wavelength of 0.3 μm to long-wavelength light with a wavelength of 2.4 μm. Select a semiconductor material that can photoelectrically convert light in this wide wavelength range. There is a need.

For example, as shown in (1) of FIG. 4 (a), a zinc selenide (ZnSe) layer having an energy gap of 2.6 eV is used as a well layer, and a zinc sulfide (ZnS) layer having an energy gap of 3.6 eV is used as a barrier. When the superlattice layer is formed by stacking as a layer, the energy gap Eg ₁ of the superlattice layer can be changed in the range of 3.1 to 2.6 eV by changing the thickness of the well layer or the barrier layer. The material has a wavelength of 0.4 to 0.48μ
It can absorb m sunlight.

Further, for example, as shown in (2) of FIG. 4 (a), a GaAs layer having an energy gap of 1.4 eV is used as a well layer, and aluminum gallium arsenide (Al _x Ga _1-x ) having an energy gap of 2.5 eV is used. As) layer is laminated as a barrier layer to form a superlattice layer, the energy gap Eg _{2 of the} superlattice layer is
By changing the thickness of the well layer or barrier layer, 1.
Since it can be varied from 8 to 1.4 eV, this material has
It can efficiently absorb sunlight of 0.69 μm to 0.89 μm.

Further, for example, as shown in (3) of FIG. 4 (a),
Hg with energy gap of 0.6 eV _1-xCd_xTe (x = 0.5)
Layer is a well layer and the energy gap is 1.5eV CdTe layer
Is formed as a barrier layer to form a superlattice layer,
Energy gap Eg of the lattice layer₃Is a well layer or barrier
By changing the layer thickness, the range is from 1.1 to 0.6 eV.
This material has a wavelength of 1.1 to 2.1 μ.
It can absorb m m of sunlight.

In FIG. 4 (a), 11 indicates the energy level at the bottom of the conduction band of each superlattice layer, and 12 indicates the energy level at the top of the valence band of each superlattice layer. .. L _w represents the thickness of the well layer, and L _B represents the thickness of the barrier layer.

When these three kinds of superlattice layers are further laminated to form a semiconductor device, the energy band diagram thereof is as shown in FIG. 4 (b). 11 in the figure shows the energy level at the bottom of the conduction band when these three types of superlattice layers are sequentially stacked, and 12 is at the top of the valence band when these three types of superlattice layers are sequentially stacked. Indicates energy level.

In this way, the energy gap is
It continuously changes from Eg ₁ to Eg ₃ and is therefore 0.4 μm
Since solar light with wavelengths up to 2.1 μm can be absorbed, and light with almost all wavelengths of sunlight can be absorbed, the absorption efficiency of solar light is improved, and therefore the photoelectric conversion efficiency is also improved and solar cells with good conversion efficiency. Can be obtained.

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings. 1 (a) is a plan view of a first embodiment of a semiconductor device of the present invention, and FIG. 1 (b) is a sectional view.

As shown in FIGS. 1 (a) and 1 (b), p-type,
Alternatively, a p-type Al _x Ga _1-x As layer (x = 0.7) having an energy gap of 2.5 eV is formed on the n-type GaAs substrate 21 by the molecular beam epitaxial growth method or the metal organic chemical vapor deposition method.
As a Å barrier layer, it is p-type and has an energy gap of 1.
The 4ev GaAs layer is used as a well layer and its thickness is from 10Å to 100
A wide energy gap superlattice layer 22 in which the energy gap gradually changes from 1.8 to 1.4 eV is formed by sequentially laminating in multiple layers while gradually changing to Å.

Table 1 shows the structure of the wide energy gap superlattice layer 22.

[0019]

[Table 1]

On the back side of the substrate 21, an n-type energy source is used.
A 20Å thick barrier layer with a CdTe layer with a luge gap of 1.5 eV
And Hg with n-type and energy gap of 0.6 eV
_1-xCd _xThe Te layer (x = 0.5) is used as a well layer and its thickness is 10Å
Layered in multiple layers while gradually changing to 100 Å
The energy gap gradually changed from 1.1eV to 0.6eV.
The narrow energy gap superlattice layer 23 is formed.
It

Table 2 shows the structure of the narrow energy gap superlattice layer 23.

[0022]

[Table 2]

And this wide energy gap superlattice layer
Striped gold-germanium alloy electrodes 24 are formed by vapor deposition on the surface of 22 so as not to block incident light. Further, an indium electrode 25 is formed on the entire surface of the narrow energy gap superlattice layer 23 by vapor deposition. The element thus formed is fixed to a supporting plate such as glass with an adhesive to obtain a semiconductor device.

The semiconductor device thus formed is
The narrow energy gap superlattice layer 23 with an energy gap of 0.6 to 1.1 eV efficiently absorbs sunlight with a wavelength of 1.1 to 2.1 μm and has an energy gap of 1.4 to 1.8 eV.
The wide energy gap superlattice layer 22 has a wavelength of 0.69 to 0.
It efficiently absorbs 89 μm sunlight, so it is 0.69 μm to 2.
Efficiently absorbs sunlight in the wavelength range up to 1 μm.

As a second embodiment of the present invention, as shown in FIG. 2, adjacent to the wide energy gap superlattice layer 22 of GaAs and Al _x Ga _{1- x} As, a p-type energy gap is provided. 2.6 eV zinc selenide (ZnSe) as a well layer
It is formed to a thickness of 100 Å, and p-type zinc sulfide (ZnS) having an energy gap of 3.6 eV is formed to a thickness of 20 Å as a barrier layer.

And, the thickness of these well layers is from 100 Å
Gradually change to 10 Å, the barrier layer thickness is 20 Å, and the energy gap is 3.1 eV from 2.6 eV by sequentially stacking multiple layers.
When a wide-energy-gap superlattice layer 22A that gradually changes is formed, the wide-energy-gap superlattice layer 22A of ZnS and ZnSe has an energy gap of 2.6 to 3.1 eV, and therefore absorbs 0.4 to 0.48 μm of sunlight. As a result, a semiconductor device having a wider range of absorption wavelength of sunlight can be obtained.

As a third embodiment of the present invention, as shown in FIG.
As shown in FIG. 3 (b), the p-type GaAs layer and Al _x Ga
N-type CdTe layer and Hg _1-x Cd _x Te (x = 0.5) layer narrow energy gap superlattice layer 23 are stacked on the wide energy gap superlattice layer 22 of _1-x As (x = 0.7) layer Then, the stripe-shaped electrode 24 may be formed on the wide energy gap superlattice layer 22, and the electrode 25 may be provided on the entire surface of the narrow energy gap superlattice layer 23.

To form such a device, as shown in FIG. 3C, a p-type GaAs layer and Al _x Ga _1-x As are formed on a GaAs substrate 21.
A wide energy gap superlattice layer 22 of (x = 0.7) layer is formed, and an n-type CdTe layer and a narrow energy gap superlattice layer 23 of Hg _1-x Cd _x Te (x = 0.5) are stacked on it. After removing the GaAs substrate 21 by polishing, the wide energy gap superlattice layer 22 is removed.
It is advisable to form a striped electrode 24 on the surface of the narrow energy gap superlattice layer 23 and to form an electrode 25 on the entire surface.

As described above, in this embodiment, the Al _x Ga _1-x As layer (x = 0.
7) and GaAs layer, CdTe layer and Hg _1-x Cd _x Te layer (x = 0.5), and superlattice layer combining ZnS layer and ZnSe layer were used.
Wide energy gap superlattice layer with an energy gap of 1.8 to 1.4 eV using ZnSe (energy gap = 2.6 eV) as a barrier layer and GaAs (energy gap = 1.4 eV) as a well layer, and ZnSe (energy gap = 2.6 eV) as a barrier layer Layer, CdTe
Wide energy gap superlattice layer with an energy gap of 1.8 to 1.5eV with (energy gap = 1.5eV) as a well layer, InAs with an energy gap of 0.5eV as a well layer, and GaAs with an energy gap of 1.4eV as a barrier layer A narrow energy gap superlattice layer having an energy gap of 1.4 to 0.5 eV may be appropriately combined and used.

As described above, according to the semiconductor device of the present invention in which a pn junction is formed by combining various types of superlattice layers having different energy gaps, it is possible to efficiently absorb the light of sunlight having a wavelength longer than the short wavelength. Therefore, there is an effect that a highly efficient solar cell can be obtained.

[0031]

As described above, according to the semiconductor device of the present invention, the semiconductor device is formed by combining the superlattice layers capable of efficiently absorbing the light in all wavelength regions of the solar light longer than the short wavelength region. Therefore, there is an effect that a highly efficient solar cell can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a plan view and a sectional view of a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of the principle of the device of the present invention.

FIG. 5 is an explanatory diagram of a conventional device and an energy band.

FIG. 6 is an explanatory diagram of a conventional device and an energy band.

[Explanation of symbols]

 11 Energy level at the bottom of the conduction band 12 Energy level at the top of the valence band 21 GaAs substrate 22, 22A Wide energy gap superlattice layer 23 Narrow energy gap superlattice layer 24, 25 Electrode

Claims (2)

[Claims] 1. An apparatus for providing a compound semiconductor layer having a heterostructure on a substrate (21), absorbing sunlight by the compound semiconductor layer, and photoelectrically converting the absorbed sunlight. Wide energy gap superlattice layer capable of absorbing wavelength light energy (22), narrow energy gap superlattice layer capable of absorbing long wavelength light energy of the sunlight
A semiconductor device characterized in that (23) is laminated or provided with a substrate (21) sandwiched therebetween so as to be able to absorb the light energy in the entire wavelength region of the sunlight. 2. The thickness of the wide energy gap superlattice layer (22), the barrier layer of the narrow energy gap superlattice layer (23), and the well layer according to claim 1, are changed stepwise or continuously. Superlattice layer (22,23)
The semiconductor device is characterized in that it is possible to continuously change the energy gap of the solar cell and absorb the light energy of various wavelengths of the sunlight.