JPH0447453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amorphous silicon semiconductor and a method for manufacturing the same, and particularly to a photovoltaic device and a method for manufacturing the same.

It was discovered by WESpear et al. that the conductivity of amorphous silicon obtained by plasma decomposition of silane (SiH ₄ ) could be greatly changed by doping it with PH ₃ or B ₂ H ₆ ( Since solar cells using amorphous silicon were prototyped by DE Carlson et al. (1976), they have attracted attention, and research has been actively conducted to improve the efficiency of amorphous silicon thin-film solar cells.

Research has shown that amorphous silicon thin-film photovoltaic devices can be structured as shot-key barrier type, pin type, MIS type, or heterostructure type, of which the first three are considered to be promising as high-efficiency solar cells. . i.e. 5.5 for shot key barrier type.
% (DE Carlson et al., 1977), 4.8% for MIS type
(JIB Wilson et al., 1978), and a conversion efficiency of 4.5% (Keihiro Hamakawa, 1978) has been achieved in the pin type.

However, in the film formation of such devices, the growth rate of the i-layer in particular is as slow as 1 to 2 Å/sec, and this slow growth rate has been a major impediment to manufacturing inexpensive devices. Various attempts have been made to modify the reaction conditions in order to improve these drawbacks. For example, attempts have been made to increase the growth rate by increasing the power in glow discharge. However, as the power is increased, the effect of plasma bombardment increases, and the film quality deteriorates [JCKnights: Appl. Phys. Lett. 35(3) 244 (1979)].
Alternatively, attempts have been made to increase the growth rate by adjusting the operating pressure or changing the substrate temperature, but these methods lead to a decrease in film quality (especially electrical properties). It had drawbacks.

As a result of intensive research efforts focused on increasing the growth rate of thin films without deteriorating film quality, the present inventors have found that during glow discharge decomposition, the photolysis reaction is assisted by light having a wavelength of preferably 5000 Å or less. We have discovered that by using this method, thin films with good electrical and optical quality can be obtained at a practical growth rate.

Surprisingly, it was also discovered that the doping efficiency can be improved to a considerable extent by irradiating the above light in the film formation of p-type or n-type amorphous silicon semiconductors. I've reached it.

The details will be explained below.

The amorphous silicon-based semiconductor of the present invention can be used as an auxiliary when decomposing a silicon compound gas or a silicon compound gas mixed with a diluent gas by high frequency glow discharge or direct current glow discharge using a capacitive coupling method or an inductive coupling method. can be obtained by using a photolysis reaction as described below. As silicon compounds, silane (SiH ₄ ) or its derivatives,
Fluorinated silane (SiH ₄ ) or its derivatives or mixtures thereof are mainly used. As the diluting gas to be mixed with the silicon compound, hydrogen, argon gas, helium, a hydrogen or nitrogen or fluorine compound of carbon, a hydrogen or fluorine compound of nitrogen, or a mixture thereof is used. . The concentration of silicon compounds in the mixed gas is usually 0.5% or more. Of course, there is no problem even if the dilution gas is not used.

The conditions for glow discharge decomposition may be the same as those generally adopted, for example, as described in JP-A-52-122471.
Those described in Japanese Patent Application Laid-Open No. 55-68681, etc. can be used.

Amorphous silicon is produced by glow discharge decomposition.
Semiconductors made of amorphous silicon carbide, amorphous silicon nitride, or a mixture thereof (hereinafter referred to as amorphous silicon-based semiconductors) can be manufactured by doping with elements from the periodic table group. By doping a p-type amorphous silicon-based semiconductor with an element of the periodic table, an n-type amorphous silicon-based semiconductor can be obtained.

In the present invention, during the growth of at least one of the p-layer, i-layer, or n-layer, light (usually
20m at a wavelength of 5000Å or less, preferably 4200Å or less
The growth rate of the layer is greatly increased by irradiating the layer with light having an intensity of W/cm ² or more, preferably 50 W/cm ² or more. Alternatively, a front chamber may be provided immediately before the reactor in which glow discharge is performed, and the above-mentioned light may be irradiated onto the front chamber.

There are no particular restrictions on the wavelength of the irradiated light as long as it is 5000 Å or less, and as long as its intensity is 20 W/cm ² or more, but due to economic considerations such as energy costs and problems with the window material that inputs the light, the wavelength In terms of strength, it is preferably 700 Å or more, and in terms of strength, it is preferably 1000 W/cm ² or less.

The effects of the present invention are that the growth rate can be significantly increased without impairing the film quality represented by the electrical properties, and that the doping efficiency can also be improved.

The amorphous silicon semiconductor of the present invention can be applied to solar cells, optical switches, photodetectors, photoreceptor materials, etc. in the same way as ordinary amorphous silicon semiconductors. The present invention will be described in detail by taking as an example the case where the present invention is applied to a solar cell which is a photovoltaic element.

A solar cell to which the present invention can be applied is a type in which sunlight is irradiated from the p-layer side, such as a structure of glass/transparent electrode/p-i-n amorphous silicon/aluminum, or a solar cell that irradiates sunlight from the n-layer side. Types that emit light, such as stainless steel/p-i-n amorphous silicon/transparent electrode configurations, etc.
There are various types. Other examples include structures in which a thin insulating layer is provided between the p-layer and the transparent electrode, a thin metal layer is provided, a shot key barrier type, and an MIS type. In short, as described below, the solar cell may have any configuration as long as it has an active layer of intrinsic amorphous silicon.

The substrate used is a transparent electrode (ITO,
Glass or polymer film with vapor-deposited SnO ₂ , etc.
Any substrate used in typical solar cell construction can be used, such as metal.

Approx. obtained by glow discharge decomposition of silicon compounds or silicon compounds mixed with diluent gas.
The i-layer is made of intrinsic amorphous silicon, which has a carrier lifetime of 10 ^-7 seconds or more, a local level density of about 10 ¹⁷ cm ^-2 eV ^-1 or less, and a mobility of 10 ^-3 cm ² /V sec or more. For example, a pin junction structure is formed in which a p-type doped semiconductor and an n-type doped semiconductor are connected. A typical configuration of a solar cell using a pin junction is a structure of transparent electrode/p-type amorphous semiconductor/i-type amorphous semiconductor/n-type amorphous semiconductor/electrode, and light is irradiated from the transparent electrode side. The transparent electrode
ITO and SnO _{2 ,} particularly SnO ₂ , are preferred, and may be used by being vapor-deposited on a glass substrate in advance, or may be directly vapor-deposited on a p-type amorphous semiconductor. The thickness of the p layer on the side exposed to sunlight is approximately 30 to 300 Å, preferably 50 to 200 Å.
The thickness of the i-layer is about 2,500 to 10,000 Å.
The n-layer is also a layer for establishing ohmic contact, and its thickness is not limited, but approximately 150 to 600 Å is used.

Another typical configuration is a transparent electrode/n-type amorphous semiconductor/i-type amorphous semiconductor/p-type amorphous semiconductor/electrode structure, in which sunlight is irradiated from the transparent electrode side. The thickness of the n-layer on the side to which light is irradiated is approximately 30 to 300 Å, preferably 50 to 200 Å, and the thickness of the i-layer is generally 2,500 to 10,000 Å. The thickness of the p layer is not limited, but is approximately
150-600 Å is used. The material and vapor deposition method for the transparent electrode are the same as before.

Next, the effects of the present invention will be explained with reference to examples, but the present invention is not limited to the following examples.

Control Example Glow discharge decomposition was performed using a quartz reaction tube with an inner diameter of 11 cm and a high frequency of 13.56 MHz at a substrate temperature of 250°C.
I-type amorphous silicon was obtained by glow discharge decomposition of silane diluted with hydrogen at 5 Torr. N-type amorphous silicon is made of silane diluted with hydrogen and phosphine (PH ₃ ) (PH ₃ /SiH ₄ = 0.5 mol%)
was similarly obtained by glow discharge decomposition. P-type amorphous silicon was similarly obtained by glow discharge decomposition of silane diluted with hydrogen and diborane (B ₂ H ₆ ) (B ₂ H ₆ /SiH ₄ =0.2 mol %). The growth rate of the i-layer was 1.8 Å/sec. In addition, 20
The dark conductivity at °C is 4×10 ^-3 respectively.
(Ω・cm) ^-1 and 2×10 ^-2 (Ω・cm) ^-1 .

The structure of the solar cell is to grow amorphous silicon in the order of p-type, i-type, and n-type on the SnO ₂ surface of a glass substrate with a 25Ω/□ SnO ₂ thin film, and finally evaporate 3.3 mm ² of aluminum. It was something that could be done. Next, solar cell characteristics were investigated using an AM-1 (100 mW/cm ² ) solar simulator. p
The characteristics of the solar cell according to the above structure, in which the layer has a thickness of 135 Å, the i-layer has a thickness of 500 Å, and the n-layer has a thickness of 500 Å, are short-circuit current.
Jsc=10.3mA/cm ² , open circuit voltage Voc=0.75volts,
The conversion efficiency η was 4.6%.

Example 1 A CaF ₂ window was provided in a part of the same reaction tube as in the control example,
The light beam from the light source can be introduced onto the top surface of the substrate parallel to the substrate surface. The light source is a low-pressure xenon lamp with continuous light in the wavelength range of 1500 to 2000 Å,
The light was applied through the CaF ₂ window at an intensity of 50 mW/cm ² . Other conditions were the same as in the control example.

The growth rate of the i-layer is 7 Å/sec, and the growth rate of the p-layer and n-layer is 20
The dark conductivity at ℃ is 8×10 ^-3 respectively.
(Ω・cm) ^-1 and 5×10 ^-2 (Ω・cm) ^-1 .

Furthermore, a solar cell having the same thickness as the control example was manufactured using this manufacturing method. The characteristics of the solar cell were: Jsc=11.9 mA/cm ² , Voc=0.79 volts, and η=5.7%.

Thus, the growth rate of the i-layer was approximately four times that of the case without irradiation with light. Also, 20℃ of p layer and n layer
The dark electrical conductivity in both cases was improved by about 2 times. These improvements improved solar cell performance by 24%.

Example 2 A high-pressure xenon lamp was used as the light source, and after removing the wavelength region of 5000 Å or more with a filter,
Everything was the same as in Example 1, except that a light beam was made incident through the CaF ₂ window at an intensity of 20 mW/cm ² .

The growth rate of the i-layer was 4 Å/sec, which was about twice the growth rate when no light was irradiated.

Example 3 An antechamber for carrying out the photolysis reaction was installed immediately before the glow discharge decomposition reactor, and a LiF window was provided in it, from which continuous light was emitted in the wavelength range of 1200 to 1800 Å. Light with an intensity of 30 mW/cm ² was incident from a low-pressure krypton lamp as a light source. Other conditions were the same as the control example.

The growth rate of the i-layer is 10 Å/sec, and the growth rate of the p-layer and n-layer is 20 Å/sec.
The dark conductivity at °C is 2.5×10 ^-2 respectively.
(Ω·cm) ^-1 and 7×10 ^-2 (Ω·cm) ^-1 , and the growth rate and doping efficiency were greatly improved.

Example 4 The light source used in Example 3 was used, and only the window material of the device used in Example 1 was changed to LiF.
Silane, siborane, and methane (CH ₄ ) diluted with hydrogen are prepared as SiH ₄ /CH ₄ =1, B ₂ H ₆ /(SiH ₄ +
The procedure was the same as in Example 1 except that CH ₄ ) was introduced at a flow rate of 0.2 mol %. The dark electrical conductivity (20° C.) of the obtained p-layer was 4×10 ⁻⁵ (Ω·cm) ⁻¹ . In addition,
The dark electrical conductivity of the p-layer obtained when other conditions are the same and no light is irradiated is 5 × 10 ^-6 at 20°C.
(Ω・cm) ^-1 .

Claims (1)

[Claims] 1. At least during the formation of the i-layer film, a photolysis reaction using light with a wavelength of 5000 Å or less is auxiliary to plasma decompose a silicon compound, thereby forming a pin junction of an amorphous silicon semiconductor. Method for manufacturing an electromotive force device. 2. The method for manufacturing a photovoltaic device according to claim 1, wherein during the plasma decomposition, doping is performed with an element belonging to a group or groups of the periodic table. 3. Claim 1, wherein the amorphous silicon-based semiconductor is amorphous silicon, amorphous silicon carbide (a-SiC), amorphous silicon nitride (a-SiN), or a mixture thereof. Or the method for manufacturing a photovoltaic device according to item 2. 4. The method for manufacturing a photovoltaic device according to claim 1 or 2, wherein the intensity of the light used for the photodecomposition reaction is 20 mw/cm ² or more.