JPH07254568A - Amorphous silicon germanium film and its manufacture - Google Patents

Abstract

PURPOSE:To make it possible to form an amorphous silicon germanium membrane on a substrate having a relatively low melting point with a high light conductivity in the undoped case and with a high dark conductivity in the doped case by forming an amorphous silicon germanium membrane having a specific light conductivity. CONSTITUTION:A non-doped amorphous silicon germanium membrane with a light conductivity,higher than 1X10<-7>S/cm or a doped amorphous silicon germanium membrane with a dark conductivity of higher than 1X10<-7>S/cm is formed on a substrate with a melting point of less than 290 deg.C. Because of this, the amorphous silicon germanium membrane is formed by plasma cracking of a mixed gas containing hydrogenated silicon gas and hydrogenated germanium gas by using ultrashort wave having a frequency range from 30MHz to 300MHz. The light conductivity means the conductivity measured under the condition where AM1.5 light by a solar simulator is incident normal to the membrane at the intensity of 100mW/cm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous silicon-germanium film used as a solar cell and a method for producing the same.

[0002]

2. Description of the Related Art An amorphous silicon-germanium film can be made to have a smaller optical band gap continuously by increasing the germanium content. It is used to make solar cells with high conversion efficiency. Bright conductivity of 1 × 10 ^-7 S /
As a method for producing an amorphous silicon-germanium film having a thickness of cm or more, for example, "Jouna by K. Nozawa et al.
l of Non-Crystalline Solids 59 & 60 (1983) p.533 "is known.
A parallel plate double-pole glow discharge using a short wave of 6 MHz decomposes a mixed gas of SiH ₄ gas and GeH ₄ gas into plasma, and non-doped amorphous silicon on a substrate heated to 200 to 250 ° C. It forms a germanium film. However, in this method, a non-conductive material having a bright conductivity of 1 × 10 ⁻⁷ S / cm or more is used.
In order to obtain an amorphous silicon-germanium film having a high temperature, the substrate temperature must be as high as 200 ° C. or higher, and there is a problem that a substrate having no heat resistance higher than that cannot be used. Also, "Jounal of Non-C" by A. Matsuda et al.
rystalline Solids 97 & 98 (1987) p.1367 "is a method in which a mixed gas of SiH ₄ gas and GeH ₄ gas is plasma decomposed by a three-pole glow discharge provided with an intermediate electrode using a short wave of 4 MHz. , A non-doped amorphous silicon-germanium film is formed on a substrate heated to 200 to 250 ° C. However, also in this method, a non-doped amorphous silicon-germanium film having a bright conductivity of 1 × 10 ⁻⁷ S / cm or more is used. In order to obtain an amorphous silicon-germanium film, the substrate temperature must be as high as 200 ° C. or higher, and there is a problem that a substrate having no heat resistance higher than that cannot be used.

On the other hand, in applications such as solar cells in which an amorphous silicon-germanium film is used, there are demands for weight reduction of products, improvement of productivity, flexibility for curved surface processing, cost reduction and the like. Materials with a low melting point and plastic materials have the advantage that the processing cost is low because they can be molded into any shape at low temperatures, and plastic materials have the advantages that they can be light in weight and are difficult to break. Therefore, it is desirable to form high quality amorphous silicon-germanium films on these materials. If plastic, especially a general-purpose plastic film such as a polyester film, can be adopted as the substrate, it is possible to meet the above requirements together with the introduction of roll-to-roll type production equipment using a long substrate. However, general-purpose plastics do not have heat resistance of 200 ° C. or higher (operating temperature range), and it is desired to lower the temperature when forming an amorphous silicon-germanium film. Further, in order to reduce the temperature decrease during the formation of the amorphous silicon-germanium film, in order to reduce the warpage and the peeling of the film due to the difference in the thermal expansion coefficient between the substrate and the amorphous silicon-germanium film,
It is also effective when using a substrate such as glass or metal having high heat resistance. In a solar cell, a transparent conductive film is used to guide light into the element, and a transparent conductive film is formed on a substrate.
The diode and the back electrode are laminated in this order. Further, in a liquid crystal display, a transparent conductive film is used to transmit light from a backlight, but when silicon nitride is formed as a protective film of a thin film transistor which is a driving element, silicon nitride is not formed on the transparent conductive film. Then, the silicon nitride is patterned so as to cover only the thin film transistor and the wiring portion. Thus, in the solar cell and the liquid crystal display, the silicon film or the silicon compound film is laminated on the transparent conductive film. As the transparent conductive film, an oxide film such as ITO (tin oxide-doped indium oxide), tin oxide, or zinc oxide, which can be made thin and has a low resistance, is used.

However, when a silicon film or a silicon compound film is deposited on the transparent oxide conductive film by plasma decomposition, oxygen atoms are extracted by excited hydrogen atoms in the plasma and are damaged, There are problems that the resistance value increases, the surface becomes rough, and the transmittance decreases. Further, there is a problem that diffusion of metal atoms into the semiconductor film caused by abstraction of oxygen atoms and deterioration of characteristics of the semiconductor film due to diffusion. Damage to excited hydrogen atoms in plasma is caused by ITO in the transparent conductive oxide film.
, And then tin oxide, and zinc oxide is said to have the best plasma resistance. Since the resistance value can be lowered in the order of ITO, tin oxide, and zinc oxide, there is a trade-off relationship between low resistance and plasma resistance. Attempts have been made to stack ITO, tin oxide, and zinc oxide on a substrate in this order to achieve both low resistance and plasma resistance. However, even zinc oxide having the highest plasma resistance is exposed to hydrogen plasma. It causes a decrease in transmittance. Also, a zinc oxide film with high plasma resistance can be obtained by raising the temperature of the substrate to 300 ° C. However, such a high substrate temperature is adopted when a substrate having relatively low heat resistance such as plastic is used as the substrate. Is difficult.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a bright conductivity of 1 × 10 ⁻⁷ S on a substrate having a low melting point.
/ Cm or more of non-doped amorphous silicon-
Germanium film and dark conductivity of 1 × 10 ^-7 S / cm
An object of the present invention is to provide a doped amorphous silicon-germanium film and a method for manufacturing the same.

[0006]

The object of the present invention is achieved by the following constitution and manufacturing method.

That is, it is an amorphous silicon-germanium film formed on a substrate having a melting point of 290 ° C. or less, and has a bright conductivity of 1 × 10 ⁻⁷ S / cm or more (non-doped). Hydrogenated silicon gas using an amorphous silicon-germanium film, an amorphous silicon-germanium film having a dark conductivity of 1 × 10 ⁻⁷ S / cm or more (doped) and an ultrashort wave in a frequency range of 30 MHz to 300 MHz. A method for producing an amorphous silicon-germanium film, which comprises forming an amorphous silicon-germanium film by plasma-decomposing a mixed gas containing hydrogen and a germanium hydride gas.

Doped Amorphous Silicon-
The germanium film is amorphous silicon in which boron or phosphorus is introduced to form a p-type or n-type semiconductor.
Refers to a germanium film. The non-doped amorphous silicon-germanium film refers to an amorphous silicon-germanium film which is an intrinsic semiconductor to which boron or phosphorus is not introduced. However, when a small amount of impurities that can be ignored is contained, it is regarded as a non-doped amorphous silicon-germanium film.

It is important that the non-doped amorphous silicon-germanium film has a bright conductivity of 1 × 10 ⁻⁷ S / cm or more, and more preferably 1 × 10 ⁻⁶ S / cm or more. The doped amorphous silicon-germanium film has a dark conductivity of 1 × 10 ⁻⁷ S /
cm or more is important, 1 × 10 ^-6 S / cm
It is more preferable that the above is satisfied. Bright conductivity means 100mW of AM-1.5 light from a solar simulator.
/ Cm ² refers to the conductivity measured with the film vertically incident on the film, and the dark conductivity refers to the conductivity measured with the film exposed to no light. The bright conductivity and the dark conductivity are measured by, for example, a direct current two-terminal method.

In the non-doped amorphous silicon-germanium film, when the light conductivity is small, the conversion efficiency of the solar cell is low when it is used for the i-type layer of the pin diode forming the solar cell. On the other hand, in the doped amorphous silicon-germanium film, when the dark conductivity is small, the conversion efficiency of the solar cell is low when it is used for the p-type layer and / or the n-type layer of the pin diode forming the solar cell.

In the non-doped amorphous silicon-germanium film, the light-dark conductivity ratio is 2 × 10.
It is preferably ² or more, and the light-dark conductivity ratio is 5 × 10
More preferably, it is ² or more. The light-dark conductivity ratio is the value of (bright conductivity / dark conductivity). If this value is low, the open-circuit voltage will be small when used in a solar cell even if the light conductivity is large, and the conversion efficiency will be low. Becomes smaller.

To increase the light absorption efficiency of the tandem solar cell,
In order to improve the conversion efficiency, the optical bandgap of the non-doped amorphous silicon-germanium film is preferably 1.2 to 1.7 eV.

The ratio of germanium atoms contained in the amorphous silicon-germanium film is germanium /
It is expressed by (silicon + germanium), and it is preferable that this value is 20% or more in order to make the optical band gap 1.7 eV or less. The composition ratio of germanium and silicon can be investigated by Auger spectroscopy.

Next, a method of manufacturing the amorphous silicon-germanium film according to the present invention will be described.

That is, a method of forming an amorphous silicon-germanium film on a substrate by plasma-decomposing a gas containing a silicon hydride gas and a germanium hydride gas by using an ultrashort wave having a frequency of 30 MHz or more and 300 MHz or less. is there.

Here, it is important that the frequency of the power supply used for plasma decomposition is in the range of 30 MHz or more and 300 MHz or less. When a film is formed using a high frequency of less than 30 MHz as a power source, the electron density of plasma does not increase so much, the deposition rate decreases, and the self-bias of the substrate increases, resulting in plasma damage. The conductivity of the film may decrease. When an ultra-short wave with a frequency exceeding 300 MHz is used as a power source, impedance matching is difficult, it is difficult to efficiently turn on the power to the electrodes, and it is difficult to form a film having a uniform thickness over a large area. Furthermore, the frequency of the power supply used for plasma decomposition is 55 MHz or more and 200 M or more.
It is more preferable to use ultra-high frequency waves having a frequency of Hz or less.

The temperature of the substrate is adjusted to 1 by using the ultrashort wave having a frequency in the range of 30 MHz to 300 MHz.
Even if the temperature is kept below 70 ° C., it is possible to form a high-quality amorphous silicon-germanium film on the substrate, which has a high light conductivity when it is non-doped and a high dark conductivity when it is doped. Therefore, a high-quality amorphous silicon-germanium film can be formed even on a material substrate such as a plastic material having a low melting point and low heat resistance. Specifically, an amorphous silicon-germanium film having a large light conductivity or dark conductivity can be easily formed on a substrate having a melting point of less than 290 ° C. and further on a substrate having a melting point of 240 ° C. or less.

Of course, the manufacturing method according to the present invention is preferably applied not only to a substrate having a melting point of 290 ° C. or lower, but also to a case where an amorphous silicon-germanium film is formed on a substrate having a melting point of higher than 290 ° C. Even in such a substrate, by lowering the temperature of the substrate, deformation due to strain of the substrate, deformation due to a difference in thermal expansion coefficient with the amorphous silicon-germanium film, or peeling of the amorphous silicon-germanium film from the substrate is prevented. be able to.

As the substrate, a plastic material, a metal material, a ceramic material, silicate glass, quartz, silicon or the like can be used. Of these, it is preferable to employ a flexible substrate, and as the flexible substrate, a plastic material, a metal material, a part of a ceramic material, or the like can be used.

As the silicate glass, barium borosilicate glass or aluminum borosilicate glass containing no sodium can be adopted. In the case of silicate glass containing sodium, it is preferable that the surface thereof is coated with a barrier layer such as a silicon oxide film in order to prevent elution of sodium.

As the flexible substrate, as described above, a plastic material, a metal material, a part of a ceramic material, or the like can be used. Specifically, it is molded into a thin plate or film. Examples include ceramic materials, metal materials and plastic materials. Since the flexible substrate can be wound in a roll shape, when a film is formed on the flexible substrate, it can be manufactured using a film forming apparatus equipped with a long substrate traveling system, and productivity can be improved. There are advantages. In addition, it has advantages that it can be easily transported and that it can be processed into a product having a curved surface. Furthermore, when a plastic material is used as the flexible substrate, the weight per area of the substrate can be made lighter than that of the ceramic material or the metal material.
There are advantages that the weight of germanium products can be reduced and that the film forming apparatus can be simplified.

Examples of the plastic material include polyesters such as polyethylene terephthalate, polyethylene naphthalate and polycarbonate, polyolefins such as polypropylene, polyarylene sulfides such as polyphenylene sulfide, polyamides, aromatic polyamides and polyether ketones. And polyimides can be used. Of these, the melting point is 290
As for those below ℃, polyethylene terephthalate,
Acetate, polyphenylene sulfide, and the like are preferably used, and those having a melting point of 240 ° C. or lower include polycarbonate, polystyrene, nylon, polypropylene, polyvinyl chloride, and the like, and are preferably used. When these are used in the form of a film, they are preferably biaxially stretched from the viewpoint of mechanical stability and strength. The heat resistance of a plastic material varies depending on the molding method, additives, usage method and the like and cannot be determined in a general manner, but an index called a usage temperature range in which mechanical properties are generally maintained can be used as a standard.

When the substrate is transparent for solar cell applications, a transparent conductive film is first formed on the substrate, and a p-type or n-type doped silicon-based semiconductor film is formed on the transparent conductive film.
Then, a non-doped amorphous silicon-germanium film and a doped silicon-based semiconductor film of the opposite type to the silicon-based semiconductor film directly above the transparent conductive film are stacked in this order to form a pin-type diode. As the silicon-based semiconductor film, in addition to Si such as amorphous silicon, SiC, SiGe, SiAl, SiGa, SiS,
Examples include SiSn. As the transparent conductive film, ITO, tin oxide, fluorine-doped tin oxide, zinc oxide, zinc oxide-aluminum oxide, or other oxides or a laminated body thereof can be preferably used because of high transparency and low resistance. ITO
It is preferable that the amount of tin oxide dope is 2 to 20% by weight. These oxide transparent conductive films do not have good resistance to excited hydrogen atoms and increase resistance and decrease transparency when plasma-decomposing a gas containing a silicon hydride gas to form an amorphous silicon-germanium film. It often causes surface roughness. Especially IT
O and tin oxide have poor resistance, and the higher the temperature, the more the resistance value increases, the transparency decreases, and the surface becomes more rough. The surface roughness may serve as a core of deposition when an amorphous silicon-germanium film is laminated on the surface, and may cause formation of coarse particles and white turbidity. Further, since hydrogen excited by plasma has a high permeability to a thin film, for example, at a low substrate temperature, 7
Even after forming a doped silicon-based semiconductor film having a thickness of 0 nm or less, if a non-doped amorphous silicon-germanium film is formed thereon without special consideration, the transparent conductive film is still damaged. According to the present invention, a high-quality amorphous silicon-germanium film can be formed at a low substrate temperature, and an increase in resistance value and a decrease in transparency of an oxide transparent conductive film can be suppressed. In the plasma decomposition by the ultra-short wave of the present invention, the potential of the plasma is small, so that the damage to the transparent conductive film from the plasma can be further reduced, and the effect of suppressing the characteristic deterioration of the transparent conductive film is great.

As the film forming apparatus, a parallel plate capacitively coupled plasma CVD apparatus can be used. The plasma energy used for decomposition is preferably 80 mW / cm ² or more and 1 W / cm ² or less per electrode area of the cathode. As the bonding state of the hydrogen atom with the silicon atom, there are a Si-H state in which one hydrogen atom is bonded to the silicon atom and a Si-H ₂ state in which _two hydrogen atoms are bonded to the silicon atom. The state of Si—H ₂ is not preferable because it becomes an obstacle to the silicon network and causes defects to be formed. At a low substrate temperature, for example 170 ° C. or lower, the value of (the number of hydrogen atoms in the state of Si—H ₂ / the number of hydrogen atoms in the state of Si—H) is a value in the silicon-based semiconductor thin film formed by the plasma CVD method. In many cases, the plasma energy is 80 mW / cm ^{2 in} plasma decomposition using ultrashort waves.
By the above, (the number of hydrogen atoms in the state of Si-H ₂ / Si
The value of (the number of hydrogen atoms in the -H state) can be reduced. On the other hand, when plasma decomposition is performed with energy larger than 1 W / cm ² , the conductivity of the film may be reduced due to plasma damage. Plasma energy used for decomposition is 100 mW / cm ² or more and 500 mW / cm
It is more preferably ² or less. The bond state of hydrogen atoms and silicon atoms and the ratio of the number of bonds can be measured by FI-IR.

The distance between the electrode substrates is preferably 8 mm or more and 80 mm or less. If it is less than 8 mm, the electrical conductivity of the film may be reduced due to plasma damage, and if it is more than 80 mm, discharge may be difficult or the deposition rate may be reduced, which may be disadvantageous in practical use. Also,
The product of the distance between the electrode substrates and the pressure of the plasma atmosphere is 12
A range of mm · Torr or more and 18 mm · Torr or less is preferable in order to balance the deposition rate and the in-plane uniformity of the deposition rate. The product of the distance between the electrode substrates and the pressure of the plasma atmosphere is less than 12 mm · Torr or 18 m
If it exceeds m · Torr, the deposition rate will be low or the in-plane uniformity of the deposition rate will be poor.

The mixed gas containing the silicon hydride gas and the germanium hydride gas used for the decomposition is a mixed gas of the silicon hydride gas and the germanium hydride gas when a non-doped amorphous silicon-germanium film is formed, Alternatively, hydrogen, helium, neon, argon, a mixed gas of at least one gas selected from the group of xenon, a silicon hydride gas and a germanium hydride gas, in the case of forming a doped amorphous silicon-germanium film Is a mixed gas of a silicon hydride gas, a germanium hydride gas and a gas containing boron or a gas containing phosphorus, or at least one gas selected from the group of hydrogen, helium, neon, argon and xenon and a silicon hydride gas. And germanium hydride gas and boro A mixed gas of a mixed gas of the gas having a gas or phosphorus having. Examples of the hydrogenated silicon gas include SiH ₄ , Si ₂ H ₆ , Si ₃ H ₈ and S.
such _{iH 2 Cl 2, SiH 2 F} 2, SiHF 3, SiF 4 can be employed. As the germanium hydride gas,
GeH ₄ , GeF _4, etc. can be adopted. As the gas containing boron, B ₂ H ₆ , B (CH ₃ ) ₃ , BF ₃ or the like can be adopted. PH ₃ or the like can be adopted as the gas containing phosphorus.

The amorphous silicon-germanium film according to the present invention is an intrinsic semiconductor or a p-type or n-type semiconductor film, is formed on a substrate, and is an intrinsic semiconductor layer, a p-type semiconductor layer, an n-type semiconductor layer, a transparent conductive film. A diode is formed by laminating a film, a metal film, an insulating film or the like, and is used as a solar cell or the like. In particular, it is suitable for use in combination with an amorphous silicon pin diode in a tandem type solar cell having a plurality of pin junctions.

[0028]

【Example】

[Characteristics Measurement / Evaluation Method] (1) Conductivity Measurement The conductivity is measured by providing a coplanar type electrode by gold vapor deposition, applying a voltage at two terminals, and measuring a current. Was calculated. AM-1.5, 100 mW / cm ² with a solar simulator when measuring the light conductivity.
Was irradiated at room temperature. The dark conductivity was measured in a shield box that can completely block light. The light-dark conductivity ratio is a value of (bright conductivity / dark conductivity).

(2) Measurement of Optical Band Gap The fundamental absorption edge spectrum was measured using a visible light spectroscope, and the result was obtained by plotting the square root of hωα (ω) / 2π on the vertical axis and hω / 2π on the horizontal axis. The section of the extrapolation line of the straight line portion obtained when represented in the graph was taken as the optical band gap. h is Planck's constant, ω is the frequency of light, and α is the absorption coefficient.

Example 1 As the film forming apparatus, a capacitively coupled plasma CVD apparatus having a parallel plate with an electrode area of 400 cm ² was used. The distance between electrode substrates is 30 mm, and the pressure during discharge is 0.3 Torr
And the gas flow rate is SiH ₄ : 25 sccm, GeH ₄ :
Plasma was generated at 10 sccm, H ₂ : 80 sccm, frequency of plasma excitation power: 50 MHz, and input power: 40 W. Barium borosilicate glass (melting point 11
60 ° C.) was used to form an amorphous silicon-germanium film having a thickness of 400 nm at a substrate temperature of 150 ° C. The film thus obtained has an optical band gap of 1.38e.
V, and the bright conductivity was 8.3 × 10 ⁻⁷ S / cm, which was very good. The light / dark conductivity ratio was 2.3 × 10 ² .

Barium borosilicate glass (melting point 1160 ° C.)
An amorphous silicon-germanium film having a thickness of 400 nm was formed under the same conditions using a substrate having a 200 nm ITO film (tin oxide 10% by weight) formed thereon as a substrate. The surface property of the film thus obtained was good, and the white turbidity observed in Comparative Example 1 was not present.

Comparative Example 1 An amorphous silicon-germanium film was formed in the same manner as in Example 1 except that the frequency of plasma excitation power was 13.56 MHz. The film thus obtained had an optical band gap of 1.43 eV and a bright conductivity of 7.8 × 10 ⁻⁸ S / cm, which was poor. The light / dark conductivity ratio was 9.8 × 10.

Barium borosilicate glass (melting point 1160 ° C.)
An amorphous silicon-germanium film having a thickness of 400 nm was formed under the same conditions by using a substrate having a 200 nm ITO film formed thereon as a substrate. Particles having a diameter of about 1 μm were formed on the film thus obtained, and the film became cloudy.

Example 2 An amorphous silicon-germanium film was formed in the same manner as in Example 1 except that the frequency of plasma excitation power was 70 MHz. The film thus obtained has an optical bandgap of 1.39 eV and a bright conductivity of 1.6.
It was a good value of × 10 ^-6 S / cm. The light / dark conductivity ratio was 3 × 10 ² .

Example 3 Example 2 was repeated except that a 100 μm-thick polyethylene terephthalate film (melting point 263 ° C.) heat-treated at 170 ° C. in vacuum for 1 hour was used as the substrate and the substrate temperature was 150 ° C. An amorphous silicon-germanium film was formed in the same manner as in. The film thus obtained had an optical band gap of 1.38 eV and a bright conductivity of 1.1 × 10 ⁻⁶ S / cm, which was very good. The light / dark conductivity ratio was 3.3 × 10 ² .

Example 4 Gas flow rates were SiH ₄ : 25 sccm and GeH ₄ : 3 sc.
_{cm, PH 3 1% -H 2} : 70sccm, input power: 4
A thickness of 400 nm doped with phosphorus at a substrate temperature of 150 ° C. in the same manner as in Example 1 except that plasma was generated at 0 W and a frequency of plasma excitation power: 80 MHz.
Was formed on barium borosilicate glass (melting point: 1160 ° C.). The film thus obtained had an optical band gap of 1.55 eV and a dark conductivity of 2 × 10 ⁻⁶ S / cm, which was excellent.

Comparative Example 2 An amorphous silicon-germanium film doped with phosphorus was formed in the same manner as in Example 4 except that the frequency of plasma excitation power was 13.56 MHz. The optical bandgap of the film thus obtained is 1.59e.
V, and the dark conductivity was as small as 8.1 × 10 ^-8 S / cm, which was a defect.

Example 5 Gas flow rate and composition were SiH ₄ : 25 sccm, GeH
_{4: 3sccm, B 2 H 6} 0.5% -H 2: 70scc
A 400 nm-thick amorphous silicon-germanium film doped with boron was formed at a substrate temperature of 150 ° C. in the same manner as in Example 4 except that m was set. The optical band gap of the film thus obtained is 1.32e.
V, and the dark conductivity was 1.3 × 10 ⁻⁶ S / cm, which was very good.

Comparative Example 3 An amorphous silicon-germanium film doped with boron was formed in the same manner as in Example 5 except that the frequency of plasma excitation power was 13.56 MHz. The optical bandgap of the film thus obtained is 1.
It was 4 eV, the dark conductivity was 7.1 × 10 ⁻⁹ S / cm, which was poor.

Example 6 500 on barium borosilicate glass (melting point 1160 ° C.)
A substrate on which an ITO film of 10 nm (10 wt% tin oxide) was formed was used as a substrate. A boron-doped amorphous silicon-germanium film having a thickness of 15 nm was formed on the substrate in the same manner as in Example 5. The surface property of the amorphous silicon-germanium film thus obtained was good and no cloudiness was observed.

On the boron-doped amorphous silicon-germanium film, undoped amorphous silicon having a thickness of 500 nm was formed in the same manner as in Example 1.
A germanium film was formed. The surface property of the film thus obtained was good and there was no cloudiness.

Comparative Example 4 500 on barium borosilicate glass (melting point 1160 ° C.)
A substrate on which an ITO film of 10 nm (10 wt% tin oxide) was formed was used as a substrate. A boron-doped amorphous silicon-germanium film having a thickness of 15 nm was formed on the substrate in the same manner as in Example 5. The surface property of the amorphous silicon-germanium film thus obtained was good and no cloudiness was observed.

On the boron-doped amorphous silicon-germanium film, non-doped amorphous silicon with a thickness of 500 nm was formed in the same manner as in Comparative Example 1.
A germanium film was formed. Particles having a diameter of about 1 μm were formed on the film thus obtained, and the film became cloudy.

Example 7 Example 2 was repeated except that a substrate was made of a polyphenylene sulfide film having a thickness of 75 μm (melting point 285 ° C.) which was heat-treated at 170 ° C. for 1 hour in vacuum, and the substrate temperature was 150 ° C. Similarly, amorphous silicon
A germanium film was formed. The film thus obtained had an optical band gap of 1.39 eV and a bright conductivity of 1.5 × 10 ⁻⁶ , which was excellent. The light / dark conductivity ratio was 3.2 × 10 ² .

[0045]

EFFECT OF THE INVENTION Amorphous silicon according to the present invention
According to the germanium film and the method for manufacturing the same, the plasma conductivity of the mixed gas containing the silicon hydride gas and the germanium hydride gas is decomposed by using the ultra-short wave to keep the temperature of the substrate at 170 ° C. or less while maintaining the bright conductivity. A highly undoped amorphous silicon-germanium film and a highly doped dark amorphous silicon-germanium film can be formed. As a result, an inexpensive and relatively low heat-resistant plastic material can be used as a substrate, and an inexpensive and lightweight solar cell or the like can be provided. Further, even when a substrate having high heat resistance is used, the film can be formed while keeping the temperature of the substrate low, so that problems such as strain due to difference in thermal expansion coefficient or thermal contraction and peeling of the film are less likely to occur. You can

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Claims (12)

[Claims] 1. An amorphous silicon-germanium film formed on a substrate having a melting point of 290 ° C. or lower, which has a bright conductivity of 1 × 10 ⁻⁷ S / cm or more. film. 2. The amorphous silicon-germanium film according to claim 1, wherein the light-dark conductivity ratio is 2 × 10 ² or more. 3. An amorphous silicon-germanium film formed on a substrate having a melting point of 290 ° C. or less, characterized by having a dark conductivity of 1 × 10 ⁻⁷ S / cm or more. film. 4. An amorphous silicon-germanium film is formed on a substrate by plasma-decomposing a mixed gas containing a silicon hydride gas and a germanium hydride gas using ultrashort waves having a frequency in the range of 30 MHz to 300 MHz. A method for producing an amorphous silicon-germanium film, comprising: 5. The method for producing an amorphous silicon-germanium film according to claim 4, wherein the amorphous silicon-germanium film is formed on a substrate kept at 170 ° C. or lower. 6. The method for producing an amorphous silicon-germanium film according to claim 4, wherein the amorphous silicon-germanium film is formed on a substrate having a melting point of 290 ° C. or lower. 7. A mixed gas containing a silicon hydride gas and a germanium hydride gas is (A) a mixed gas of a silicon hydride gas and a germanium hydride gas, or (B) hydrogen, helium, neon, argon or xenon. And at least one gas selected from the group consisting of: a silicon hydride gas, a mixed gas with a germanium hydride gas, or (B) a silicon hydride gas, a germanium hydride gas, a gas containing boron or a gas containing phosphorus. Or a mixed gas of (D) at least one gas selected from the group of hydrogen, helium, neon, argon and xenon, a silicon hydride gas, a germanium hydride gas, a gas containing boron or a gas containing phosphorus. Mixed gas with mixed gas,
5. The method for manufacturing an amorphous silicon-germanium film according to claim 4, wherein 8. The frequency of the ultra high frequency wave is 55 MHz or more and 200 or more.
The method for producing an amorphous silicon-germanium film according to claim 4, wherein the frequency is in the range of MHz or less. 9. The amorphous silicon according to claim 4, wherein the power value of the ultra-high frequency divided by the area of the cathode electrode is 80 mW / cm ² or more and 1 W / cm ² or less.
Germanium film manufacturing method. 10. The method for producing an amorphous silicon-germanium film according to claim 4, wherein a doped amorphous silicon-germanium film is formed on a substrate on which a transparent conductive film made of oxide is formed. 11. A non-doped amorphous silicon layer on a substrate on which a transparent conductive film made of an oxide is formed, with a doped silicon-based semiconductor film of 70 nm or less interposed therebetween.
The method for manufacturing an amorphous silicon-germanium film according to claim 4, wherein a germanium film is formed. 12. The method for producing an amorphous silicon-germanium film according to claim 10, wherein the transparent conductive film made of an oxide is tin oxide-doped indium oxide, tin oxide, zinc oxide, or a laminated body thereof. Method.