JPS61278132A - Forming method for amorphous hydride sige film - Google Patents

Abstract

PURPOSE:To improve film quality by utilizing a photo-CVD method as a film formation method and diluting a raw material gas for forming a film with hydrogen. CONSTITUTION:Ultraviolet beams from a light source 1 excite and activate a raw material gas and hydrogen gas charged into a reaction chamber 2 while they decompose these gases and accelerate reactions, and a predetermined thin-film 5 is deposited on a substrate 4 heated by a heater 3 supported into the reaction chamber 2 similarly, thus obtaining an a-SiGe:H film. In a film formation process, hydrogen is added to the raw material gas, and dangling bonds are terminated by H. Accordingly, a localized level is reduced largely, and film quality can be improved.

Description

[Detailed description of the invention] 11 Yu 9 Satgetsu±! The present invention is a hydrogenated amorphous S containing germanium.
This invention relates to a method for forming an i-film. More specifically, the present invention relates to a method for producing a hydrogenated amorphous Si film doped with Ge that has high long-wavelength sensitivity and good film quality.

2. Description of the Related Art A typical example of an electronic device that utilizes the photovoltaic effect is a solar cell. This solar cell converts solar energy or other light energy into electrical energy, and is one of the technologies that is attracting attention as a future energy solution. The conversion of light energy into electrical energy by solar cells utilizes the photovoltaic effect, which is one of the most fundamental properties of semiconductors such as heterojunctions, pn or pin junctions, and Schottky junctions. This occurs through a mechanism in which the light is absorbed, generates electron-hole pairs, and is extracted to the outside.

By the way, hydrogenated amorphous silicon (hereinafter referred to as a-3i:H for simplicity) has recently attracted attention as a material for thin-film solar cells, and it has an absorption coefficient for light near the peak (500 nm) of the solar energy distribution that is higher than that of crystalline silicon. Compared to Si, it is about an order of magnitude larger, and the thin film formation temperature is lower.
It has interesting properties such as being able to form a film directly from raw materials by glow discharge decomposition and making it easy to form bonds.

The most important issue in the design and production of solar cells is achieving high conversion efficiency, and much research and development is underway to achieve this goal.

Therefore, recently Ge has been used as an additive element to produce hydrogenated amorphous silicon (hereinafter referred to as a-3iGe).
a-3iGe:H using a-3iGe:H as one layer
Solar cells have been proposed. For example, forbidden band width E, y1
．． In the output characteristics of an a-3iGe:H single-layer solar cell using a 4 eV a-3iGe:H film as the i-layer, the short-circuit current J. 9. The long wavelength sensitivity was as low as Om^/cuf, and was not satisfactory.

Therefore, a-3i: H/ a-3iGe:
In order to improve the conversion efficiency of the H stacked solar cell, the characteristics of the a-3iGe:H single layer solar cell, which is the second layer solar cell, especially J. It was also necessary to improve the long wavelength sensitivity.

As detailed above, a-3i has attracted attention as a material for thin-film solar cells due to its various interesting properties, and extensive research has been conducted on it. However, the development of technology suitable for practical use is highly desired.

For example, in the above a-3i:H/a-3iGe:H stacked solar cell, it is considered necessary to particularly improve the characteristics of the a-5iGe:H single-layer solar cell.

The reason why conventional products of this type are inferior in short circuit current Jse and long wavelength sensitivity is the GeH4 raw material gas flow rate ratio GeH
</If (GeH, +5iH4) is large, the forbidden band width E9
low a-3iGe: H film is produced, but Ge
generates electrical defects and increases photoconductivity (AM 1.0.10
This is because it is thought that Δσ (during 0 mW/cnf irradiation) and dark conductivity σd are deteriorated. That is, a
-3iGe:H film is required to have low E and high long wavelength sensitivity, and for this purpose, the above Δσph should be set to 10-
'(Ω・cm) -' and σ6 is 10-8~
It was necessary to lower it to about 10-'(Ω·cmν1).

Therefore, an object of the present invention is to provide a method for forming an a-3iGe:H thin film with low defects and excellent Jsc and long wavelength characteristics, and also to provide a method for forming an a-3iGe:H thin film with high conversion efficiency.
It is also an object of the present invention to provide a H/a-3iGe:H stacked solar cell.

Means for Solving the Problems The inventors of the present invention have conducted various studies and researches to solve the above-mentioned drawbacks of a-3i thin film solar cells. The present invention was completed based on the discovery that diluting the raw material gas with hydrogen is extremely advantageous in improving film quality.

That is, the method for forming the a-3iGe:H film of the present invention is to form an a-3iGe film in which Ge is added to the a-3i:H film.
: An improved method for producing a H film, characterized in that hydrogen is added to a raw material gas containing an additive source at the following ratio, and a photochemical vapor deposition (photoCVD) method is used as a thin film forming method. It is something.

The raw material gas useful in the method of the present invention is SiH
,,512Fa, SiF, or a mixture thereof can be used. On the other hand, as a raw material for Ge as an additive element, GeHa, Ge F 4 or a mixture thereof can be used.

The amount and ratio of hydrogen added when diluting the raw material gas with hydrogen needs to be appropriate.

The photo-CVD method, which is an advantageous film-forming method in the method of the present invention, can use either the mercury sensitization method or the direct excitation method, and it is possible to form a thin film using, for example, an apparatus as shown in FIG. be. According to this device, the ultraviolet light from the light source 1 excites and activates the raw material gas and hydrogen gas charged into the reaction chamber 2, and promotes decomposition and reaction. By depositing a predetermined thin film 5 on a substrate 4 heated by
e:H film can be obtained.

In the method of the present invention, ultraviolet rays having a wavelength of 0.3 μm or less are particularly useful. Further, ultraviolet rays may be used by condensing them with a lens or the like.

What is important in the production of a-3i:H/a-3iGe:H stacked solar cells is to improve the conversion efficiency, and for this purpose, as described above, the short-circuit current Jsc and long length of the a-3iGe:H single-layer solar cell are Wavelength sensitivity must be improved. This is thought to be due to the fact that Δσ and σ6 are worsened by Ge as an additive element, but the a-3iGe:H film also has a large amount of dangling bonds, that is, broken bonds. It is thought that this state exists and acts as a defect in the thin film.

Therefore, in the method of the present invention, hydrogen is added to the source gas in the film forming process, and the dangling bonds are terminated with H. As a result, the localized levels are greatly reduced, making it possible to improve the film quality.

According to the method of the present invention, by diluting the raw material gas with hydrogen, the above-mentioned dangling bonds are reduced, and the localized levels are thereby greatly reduced, making it possible to lower σ without lowering Δσph. Even when E and α are 1.4 eV, an a-3iGe:H film with good film quality can be obtained.

In the method of the present invention, the amount of hydrogen added is critical, and the ratio Hz/(Ge source + Si source + 82) is 0.25 to 0.60.
must be within the range. That is, when the quantitative ratio is 0.25 or less, the amount of hydrogen is insufficient, and the termination of dangling bonds by hydrogen is insufficient, resulting in an a-3iGc,:H film with good film quality. On the other hand, if the value is set to 0.6 or more, the amount of hydrogen gas becomes too large, resulting in microcrystallization of the film, and σd becomes too large to be used as an i-layer. It is also necessary to avoid

According to the method of the present invention, a-5 with good film quality as described above
iGe:H thin film can be advantageously formed, and this thin film has a
-3i:H/a-3iGe:H is useful in the production of H stacked solar cells. Although the present invention has been described in detail above using a solar cell as an example to simplify the explanation, the method of the present invention is of course also useful for photoreceptors, sensors, etc. that use a-3iGe:H thin films.

Furthermore, by adopting the photo-CVD method as the film-forming method,
Compared to the plasma CVD method, there is no damage to the film due to high-energy charged particles, and it is possible to obtain a high-quality a-3iGe:H film.

EXAMPLES Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is not limited in any way by the following Examples.

Example 1 5iHa as a raw material gas and Ge as an additive element Ge source
Using H+ respectively, the gas flow rate ratio GeH4/(GeH<+5
iH4) was kept constant at 0.4. On the other hand, hydrogen is added to the raw material gas mixture, and the ratio H2/(GeH4+SiH4+H2
) was changed to various values, and a-3iGe:H thin films were formed by a photo-CVD method (mercury sensitization method). Film-forming conditions were mercury temperature for sensitization of 60°C, total gas flow rate of 30-70°C.
secm, and the substrate temperature was 160°C. For the thin film thus obtained, Δσ.

and σ6 were measured, and the obtained results are shown in FIG. Here, Δσph and σ6 are measured using the electrode AI
was vacuum-deposited onto a gap type.

As is clear from Figure 2 obtained from the results in Figure 1, the ratio H
2/(GeH<+SiH4+H2> is 0.25 to 0.6
When it is within the range of 0, the ratio of ΔσPh/σ6 is large,
It can be understood that this provides a film with good photosensitivity.

As explained in detail above, the a-3iGe of the present invention:
According to the H thin film formation method, dangling bonds can be terminated by diluting the a-3iGe:H film forming raw material gas within a predetermined ratio range with hydrogen, and the film can be formed using the photo-CVD method. Based on the film, Δσ
a-3iGe with a large ph/σ6 ratio and excellent photosensitivity
: It became possible to obtain a H thin film.

Therefore, an a-3i:H film that requires an a-3iGe:H film with low E9 and high long-wavelength sensitivity as a single layer
/a-3iGe:H stacked solar cell could be obtained, and its conversion efficiency could also be greatly improved.

Furthermore, the method of the present invention can be advantageously applied to the formation of thin films on various other photoreceptors, sensors, and the like.

[Brief explanation of the drawing]

FIG. 1 shows a-3iGe obtained according to the method of the present invention:
Δσ and σ of the H film are expressed as hydrogen dilution ratio H2 of the raw material gas.
/ (GeH4+SiH<+H2), and Figure 2 is a graph plotted against a-3iGe obtained according to the method of the present invention:
ΔσPh/σ6 of the H film is expressed as hydrogen dilution ratio H2/of the raw material gas.
This is a graph plotted against (GeH4+StHa+H2). FIG. 3 is a diagram schematically showing an example of a photo-CVD apparatus for carrying out the method of the present invention. (Main reference numbers) 1...Light source, 2...Reaction chamber, 3...Heater, 4...Substrate, 5...Deposited film, 6...
... Raw material gas, 7... Vacuum exhaust pump for pressure reduction,

Claims (4)

[Claims] (1) In the method of forming a hydrogenated amorphous silicon thin film doped with germanium, photochemical vapor deposition is used as the thin film forming method, and the raw material gas containing the doping source is adjusted to a ratio of hydrogen gas flow rate to the total gas flow rate to 0. The film forming method described above is characterized in that the film is formed in a diluted state with hydrogen so as to be within the range of .25 to 0.6. (2) The raw material gas for the hydrogenated amorphous silicon is S
2. The film forming method according to claim 1, wherein the film is iH_4, Si_2H_6, SiF_4, or a mixture thereof. (3) The film forming method according to claim 2, wherein the germanium source is GeH_4, GeF_4, or a mixture thereof. (4) The film forming method according to any one of claims 1 to 3, wherein the photochemical vapor deposition method is carried out using ultraviolet light having a wavelength of 0.3 μm or less.