JP2001068484A - Manufacture of compound semiconductor thin film, solar battery using the same, composition determining method of compound semiconductor thin film and thin film formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture a compound semiconductor thin film having a composition suitable for a solar battery by controlling the composition of a compound semiconductor thin film by using that temperature variation speed of a compound semiconductor thin film varies according to the composition of a compound semiconductor thin film in a thin film formation process of groups I, III and VI elements. SOLUTION: A first compound semiconductor thin film 24 is formed by supplying group III element and group IV element on a base 23 formed of a substrate 22 wherein an Mo thin film 21 is formed. Thereafter, a second compound semiconductor thin film 25 is formed by supplying an element comprising a group I element and a group IV element on the thin film 24. Furthermore, a compound semiconductor thin film 26 consisting of group I-III-VI is formed by supplying an element comprising a group VI element on the second compound semiconductor thin film 25. In the process, one temperature lowering speed selected from the base 23 and the compound semiconductor thin film 26 is measured until it is threshold or below, and a compound semiconductor thin film of Cu/group III ratio is 1 or below is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a compound semiconductor thin film, a solar cell using the same, a method for determining the composition of a compound semiconductor thin film, and a thin film forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a compound semiconductor thin film Cu
A solar cell using (In, Ga) Se ₂ as a light absorbing layer is known. In order to obtain high energy conversion efficiency in such a solar cell, it is necessary to use a compound semiconductor thin film having large grains and a surface not Cu-rich for the light absorbing layer. In particular, Cu in the compound semiconductor thin film
It is known that when the composition ratio of the element and the group III element exceeds 1, it does not function as a solar cell.

[0003] As a method for producing a compound semiconductor thin film having a large grain and not having a Cu-rich surface, for example, a three-step method has been reported (M. Contreras).
(M. Contreras) and others in Progress in Photovoltaics
voltaics), 2, 1994, p287). In the three-step method, first, as a first step, In and Ga as Group III elements and Se as Group VI element are heated at 500 ° C.
Deposition is performed at the following substrate temperature. Next, as a second step, I
Group element Cu and group VI element Se at a substrate temperature of 5.
Deposits at 00 ° C or higher. Next, as a third step, a group III element and a group VI element are deposited at a substrate temperature of 500 ° C. or higher. Thus, in the three-stage method, the group I element C
A compound semiconductor thin film comprising u, a group III element, and a group VI element, wherein the composition ratio of Cu and the group III element in the semiconductor thin film is 1 or less can be manufactured.

[0004]

However, in the above-mentioned conventional method, it is difficult to control the composition ratio between Cu and the group III element, and it is difficult to obtain a high-quality crystal suitable for a solar cell.

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention provides a method of manufacturing a compound semiconductor thin film in which the composition ratio is easily controlled, a solar cell using the same, a method of determining the composition of the compound semiconductor thin film, and a thin film forming apparatus The purpose is to provide.

[0006]

In order to achieve the above object, a first method for producing a compound semiconductor thin film according to the present invention comprises:
In the method for producing a compound semiconductor thin film including a Group III element, a Group III element, and a Group VI element, the compound semiconductor thin film is formed by supplying the Group I element, the Group III element, and the Group VI element onto a substrate. A step of forming a thin film on the substrate, wherein the composition of the compound semiconductor thin film is controlled by utilizing a fact that the temperature change rate of the compound semiconductor thin film varies depending on the composition of the compound semiconductor thin film during the thin film forming step. It is characterized by the following. According to the first manufacturing method, the composition of the compound semiconductor thin film can be easily controlled.

The second method of manufacturing a compound semiconductor thin film of the present invention is directed to a method of manufacturing a compound semiconductor thin film including a group I element, a group III element, and a group VI element. A thin film forming step of forming the compound semiconductor thin film on the base by supplying the group VI element onto the base, wherein the thin film forming step is selected from the base and the compound semiconductor thin film. The composition of the compound semiconductor thin film is controlled using at least one temperature change rate. According to the second manufacturing method, the composition of the compound semiconductor thin film can be easily controlled.

[0008] In the first and second manufacturing methods, before the thin film forming step, the I in the compound semiconductor thin film is removed.
A step of determining a relationship between the number of atoms of group III elements and the number of atoms of group III elements in the compound semiconductor thin film, and the temperature change rate, and controlling the composition of the compound semiconductor thin film using the relationship. It is preferable to be performed. According to the above configuration, the composition of the compound semiconductor thin film can be controlled with high reliability.

In the first and second manufacturing methods, the temperature change rate includes cooling the compound semiconductor thin film (including leaving the compound semiconductor thin film at a temperature lower than the temperature of the compound semiconductor thin film without heating). It is preferable that the temperature drop rate at that time.

In the first and second manufacturing methods, the thin film forming step forms the first thin film on the base by supplying the group III element and the group VI element onto the base. A second step of forming a second thin film on the base by supplying an element containing at least the group I element and the group VI element onto the first thin film;
And a third step of supplying at least the group VI element onto the second thin film until the temperature drop rate becomes at least the threshold value or less. According to the above configuration, (the number of atoms of group I element / III
A compound semiconductor thin film having a value of the number of atoms of group elements) equal to or less than a predetermined value is obtained.

In the first and second methods for producing a compound semiconductor thin film, the thin film forming step includes the step of supplying the group III element and the group VI element onto the substrate to form a first layer on the substrate. A first step of forming a thin film;
Forming a second thin film on the base by supplying an element containing at least a group III element and the group VI element onto the first thin film until the temperature drop rate becomes greater than a threshold value; Preferably, the method includes a third step of supplying at least the group VI element onto the second thin film until the temperature drop rate becomes at least a threshold value or less. According to the above configuration, a compound semiconductor thin film in which the value of (number of atoms of group I element / number of atoms of group III element) in the compound semiconductor thin film is equal to or less than a predetermined value is obtained.

In the first and second manufacturing methods, the threshold value may be substantially equal to the number of atoms of the group I element contained in the compound semiconductor thin film and the number of atoms of the group III element contained in the compound semiconductor thin film. It is preferable that the temperature drop rates are equal. With the above structure, the number of atoms of the group I element in the compound semiconductor thin film is smaller than the number of the atoms of the group III element, and a compound semiconductor thin film suitable for a solar cell can be obtained.

In the first and second manufacturing methods, it is preferable that in the thin film forming step, the temperature of the base is from 250 ° C. to 600 ° C. According to the above configuration, a compound semiconductor thin film particularly suitable for a solar cell can be obtained.

In the first and second manufacturing methods, the group I element is Cu, and the group III element is In and G.
Preferably, the group VI element is at least one element selected from Se and S. According to the above configuration, a compound semiconductor thin film particularly suitable for a solar cell can be obtained.

Further, the method of determining the composition of a compound semiconductor thin film of the present invention is a method of determining the composition of a compound semiconductor thin film containing a group I element, a group III element and a group VI element, wherein the compound semiconductor thin film has a temperature change rate. Is characterized in that the composition of the compound semiconductor thin film is determined by utilizing the fact that the composition of the compound semiconductor thin film varies.

The thin film forming apparatus of the present invention is a thin film forming apparatus for forming a compound semiconductor thin film containing a group I element, a group III element and a group VI element on a substrate. Heating means, the group I element and the III
An element supply unit for supplying a group IV element and the group VI element onto the substrate; and the substrate and the compound for determining a composition of the compound semiconductor thin film formed on the substrate by the element supply unit. Temperature measuring means for measuring at least one temperature selected from semiconductor thin films. According to the thin film forming apparatus of the present invention, the composition can be easily controlled to form a compound semiconductor thin film.

In the thin film forming apparatus, a storage means for storing a relationship between a composition of the compound semiconductor thin film and a temperature change rate of the compound semiconductor thin film, and a temperature measured by the temperature measuring means and the relationship are used. It is preferable that the apparatus further comprises a determination means for determining the composition of the compound semiconductor thin film.

Further, the solar cell of the present invention is a solar cell having a light absorbing layer, wherein the light absorbing layer is made of a compound semiconductor thin film manufactured by the method of manufacturing a compound semiconductor thin film of the present invention. . According to the solar cell of the present invention, a solar cell having high characteristics can be obtained.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 In Embodiment 1, an example of a method for determining the composition of a compound semiconductor thin film of the present invention will be described.

The method for determining the composition of the present invention comprises the steps of:
Semiconductor thin film containing a group III element and a group VI element (hereinafter referred to as I
-III-VI compound semiconductor thin film) in some cases depending on the composition of the compound semiconductor thin film.

The group I element of the compound semiconductor thin film is, for example, Cu. The group III element of the compound semiconductor thin film is, for example, at least one element selected from In and Ga. The group VI element of the compound semiconductor thin film is, for example, at least one element selected from Se and S. Specifically, for example, Cu (In,
Ga) Se ₂ thin film, Cu (In, Ga) ₃ Se ₅ thin film, C
u (In, Ga) ₅ Se ₈ thin film, and these Cu and (I
n, Ga) or a composition in which a part of Se is replaced by S.

The composition discrimination method of the present invention is based on the new finding that the temperature change rate of the compound semiconductor thin film changes depending on the composition.

FIG. 1 shows an example of the temperature change rate of the substrate on which the Cu (In, Ga) Se ₂ thin films having different compositions are formed. The substrate used at this time was Mo on a glass substrate.
A thin film is formed, and Cu (In, Ga)
The Se ₂ thin film is formed on the Mo thin film. FIG.
Is a temperature change when the substrate at 450 ° C. is cooled (leaved in a substantially vacuum state without being heated). The temperature change of the substrate is measured from the glass substrate side using a radiation thermometer. The temperature change of the substrate is Cu (In,
To vary depending on the temperature change rate of the Ga) Se ₂ thin film, by measuring the temperature change of the substrate, Cu (I
The change in the temperature change rate of the (n, Ga) Se ₂ thin film can be determined.

The compound semiconductor thin films of solid lines A and B were formed using the thin film forming apparatus 10 described in the second embodiment. That is, a Mo thin film is formed by sputtering.
The glass substrate deposited to a thickness of μm is horizontally moved at a speed of 1 cm / min by a substrate moving mechanism, and the temperature of the substrate is 350 ° C. while controlling the pressure of In, Ga, and Se from the lower opening with an ionization vacuum gauge. And supplied on the Mo thin film. The respective pressures are as follows: Se is 2 × 10 ⁻⁵ Torr, In
Was 8 × 10 ⁻⁷ Torr and Ga was 3 × 10 ⁻⁷ Torr. Further, the substrate temperature was raised to 500 ° C., and while the glass substrate was moved, the pressure of Se was 2 × 10 ⁻⁵ To.
The rr and Cu were supplied onto the Mo thin film such that the pressure of the Cu became 3 × 10 ⁻⁷ Torr and the pressure of Ga became 2 × 10 ⁻⁷ Torr. Thus, the compound semiconductor thin film shown by the solid line A was formed. In addition, In, Ga, and Se were further supplied to the compound semiconductor thin film shown by the solid line A while maintaining the substrate temperature at 500 ° C. to form a compound semiconductor thin film shown by the solid line B.

The composition of the solid lines A and B in FIG. 1 was analyzed by electron probe mass spectrometry, and the ratio of “atoms of Cu / atoms of group III elements” in the compound semiconductor thin film (hereinafter Cu / III) Are shown in Table 1.

[0027]

[Table 1]

As is clear from FIG. 1 and Table 1, it is found that the temperature drop rate increases as the Cu / III group ratio in the compound semiconductor thin film increases. When the Cu / III group ratio was approximately 1, a temperature drop rate substantially similar to that of the line B (a temperature drop rate slightly larger than that of B) was obtained.
Therefore, (the number of atoms of Cu / II in the compound semiconductor thin film)
It can be seen that when the value of the number of atoms of the group I element) is larger than 1, the temperature drop rate rapidly increases.

Although the cause of such a change in the temperature drop rate due to the composition is not clear at present, it is considered that the change is caused by a difference in thermal emissivity (emissivity) due to a change in the composition of the compound semiconductor thin film. Can be

As described above, the temperature change rate of the compound semiconductor thin film differs depending on the composition of the compound semiconductor thin film.
By examining these relationships in advance, the composition (C
u / III group ratio). In particular, by using the composition determination method of Embodiment 1, the ratio between the number of Cu atoms and the number of Group III elements contained in the compound semiconductor thin film (hereinafter sometimes referred to as a Group I / III ratio). Can be determined. If this determination method is used, for example, when forming a group I-III-VI compound semiconductor thin film continuously on a plurality of substrates, by taking out a part, determining the composition, and feeding it back to the film formation conditions, A group I-III-VI compound semiconductor thin film having a desired group I / III ratio can be easily manufactured.

(Embodiment 2) In Embodiment 2, an example of a method for manufacturing a compound semiconductor thin film and a thin film forming apparatus according to the present invention will be described.

In the manufacturing method of Embodiment 2, the group I element and the II
When the I-III-VI group compound semiconductor thin film is formed on the substrate by supplying the group I element and the group VI element onto the substrate, the temperature change rate of the compound semiconductor thin film varies depending on the composition of the compound semiconductor thin film. Is used to control the composition of the compound semiconductor thin film. Specifically, when forming the I-III-VI group compound semiconductor thin film, the composition of the compound semiconductor thin film is controlled using at least one temperature change rate selected from the base and the compound semiconductor thin film.

FIG. 2 is a schematic view showing an example of a thin film forming apparatus which can be used in the composition determination method of the present invention.

Referring to FIG. 2, the thin film forming apparatus 10 includes a substrate introduction chamber 11, a reaction chamber 12, a substrate discharge chamber 13, a plurality of evaporation sources 14 arranged in the reaction chamber 12, a heater 1
5, a radiation thermometer 16, and a substrate moving mechanism (not shown).

The substrate introduction chamber 11 and the substrate discharge chamber 13
These are portions for introducing and discharging the base (including the substrate) 17, respectively. The substrate introduction chamber 11, the reaction chamber 12, and the substrate discharge chamber 13 may be provided with an exhaust device (not shown) if necessary.
Is evacuated to a substantially vacuum. The plurality of evaporation sources 14
A group III element, a group III element, a group VI element or a compound thereof is provided in a heating vessel. The heater 15 is for heating the substrate, and functions as a heating unit. The radiation thermometer 16 is for measuring the temperature of a substrate or the like on which the compound semiconductor thin film is formed, and functions as a temperature measurement unit. Note that a thermocouple or the like can be used instead of the radiation thermometer, but by using the radiation thermometer, it is possible to measure at least one temperature selected from the substrate and the compound semiconductor thin film without contacting the substrate. it can.

In the apparatus shown in FIG. 1, after the substrate is introduced into the reaction chamber 12, the substrate 17 is heated by the heater 15 to supply the group I, group III and group VI elements from a plurality of evaporation sources. Thus, a compound semiconductor thin film can be formed on the base 17. Thereafter, by moving the substrate 17 to the radiation thermometer 16 side, the temperature drop rate of the substrate when the substrate is cooled (when left without heating) can be measured.

Here, as described in the first embodiment, I
-Since there is a correlation between the composition of the group III-VI compound semiconductor thin film and its temperature drop rate, it was formed by examining the relationship between the composition of the compound semiconductor thin film and its temperature drop rate in advance. The Cu / III group ratio in the I-III-VI compound semiconductor thin film can be determined.

In particular, the thin film forming apparatus 10 includes storage means for storing the above relationship, and calculation means for determining the composition of the compound semiconductor thin film using the temperature measured by the radiation thermometer 16 and the relationship. The compound semiconductor thin film can be formed by automatically controlling the composition.

Next, an example of the method for producing a compound semiconductor thin film of the present invention will be described.

In the manufacturing method of the second embodiment, first, the relationship between the composition (Cu / III group ratio) of the compound semiconductor thin film to be manufactured and the temperature drop rate is determined. At this time, since the temperature drop rate changes depending on the shape of the apparatus, the structure and the shape of the base, etc., it is necessary to measure the temperature under the same conditions as the following conditions at the time of manufacturing the compound semiconductor thin film.

Next, as shown in FIG. 3A, a III film was formed on a substrate 23 comprising a substrate 22 on which a Mo thin film 21 was formed.
A thin film (first thin film) 24 is formed by supplying a group III element and a group VI element (first step). The supply of each element can be performed by an evaporation method, a sputtering method, or the like.

Thereafter, as shown in FIG. 3 (b), an element containing at least a group I element and a group VI element (which may further contain a group III element) is supplied onto the thin film 24, whereby the compound semiconductor thin film is formed. A thin film (second thin film) 25 is formed (second step). The supplied elements diffuse into the thin film 24 to form a compound semiconductor thin film 25 having a substantially uniform composition.

Thereafter, as shown in FIG. 3C, an element containing at least a group VI element (which may further include a group III element) is supplied onto the compound semiconductor thin film 25, so that the group III-III-VI Is formed (third step). In the third step, the substrate 2
3 and the compound semiconductor thin film 26, at least one temperature drop rate is measured, and the third step is performed until the temperature drop rate becomes at least a threshold value (temperature drop rate when the Cu / III group ratio is 1 or less). By performing the above, a compound semiconductor thin film having a Cu / III group ratio of 1 or less can be easily manufactured.

In the above manufacturing method, the group I element is, for example, Cu. Group III elements include In and Ga
At least one element selected from The group VI element is at least one element selected from Se and S.

In the above manufacturing method, in the second step,
At least one temperature drop rate selected from the base body 23 and the compound semiconductor thin film 26 is measured, and the above temperature drop rate is at least greater than a threshold value (temperature drop rate when the Cu / III group ratio is 1 or less). Preferably, step 2 is performed. In the second step, a compound semiconductor thin film 25 having a Cu / III group ratio larger than 1 is produced, and in the third step, a compound semiconductor thin film 26 having a Cu / III ratio of 1 or less is produced. Particularly good compound semiconductor thin films can be obtained.

In the above manufacturing method, it is preferable that the temperature of the substrate 23 is maintained at 200 ° C. to 400 ° C. in the first step, and the temperature of the substrate 23 is 200 ° C. to 700 ° C. in the second step. Is preferably maintained.
In the third step, it is preferable to maintain the temperature of the base 23 at the time of forming the compound semiconductor thin film 26 at 200 ° C. or higher and 600 ° C. or lower, and then cool the base 23 in an atmosphere of a group VI element. preferable.

According to the method of manufacturing a compound semiconductor thin film of the third embodiment, the Cu / III group ratio can be easily controlled and the I-III
A group-VI compound semiconductor thin film can be manufactured, and a group I-III-VI compound semiconductor thin film particularly suitable for solar cells having a Cu / III group ratio of 1 or less can be obtained.

Embodiment 3 In Embodiment 3, an example of a solar cell of the present invention will be described.

Referring to FIG. 4, solar cell 3 of Embodiment 4
0 denotes a substrate 31, a back electrode 32, a p-type compound semiconductor thin film 33, a buffer layer 34, which are sequentially laminated on the substrate 31,
Window layer 35, transparent conductive film 36, p-side electrode 37, n
And a side electrode 38.

As the substrate 31, for example, a glass substrate, a polyimide film, a stainless steel plate or the like can be used.
For the back electrode 32, for example, a Mo film can be used. The p-type compound semiconductor thin film 33 is a compound semiconductor thin film manufactured by the manufacturing method described in Embodiment 2, and functions as a light absorption layer. p-type compound semiconductor thin film 3
No. 3 has a Cu / III group ratio of 1 or less. The thickness of the p-type compound semiconductor thin film is, for example, not less than 0.2 μm and not more than 3 μm.
m or less. The buffer layer 34 includes, for example, Zn
An (O, OH, S) film can be used. For the window layer 35, for example, a ZnO film can be used. The transparent conductive film 36 is made of, for example, ITO (Indium Tin O 2).
xide) can be used. As the p-side electrode 37 and the n-side electrode 38, for example, a metal film in which a NiCr film and an Au film are laminated can be used.

In the solar cell according to the third embodiment, since the p-type compound semiconductor thin film 33 whose Cu / III group ratio is controlled to 1 or less is used as the light absorbing layer, a solar cell with high conversion efficiency can be obtained.

The solar cell described in the third embodiment is an example. If the solar cell includes a compound semiconductor thin film manufactured by the method for manufacturing a compound semiconductor thin film of the present invention as a light absorbing layer, the other structure is the same. Any structure may be used.

[0053]

As described above, according to the method for producing a compound semiconductor of the present invention, a group I-III-VI compound semiconductor thin film having a composition suitable for a solar cell can be easily produced.

According to the composition determining method of the present invention,
-The Cu / III ratio of the III-VI compound semiconductor thin film can be easily determined.

Further, according to the thin film forming apparatus of the present invention, it is possible to easily manufacture a group I-III-VI compound semiconductor thin film having a composition suitable for a solar cell.

According to the solar cell of the present invention, a solar cell having high characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a Cu / III group ratio of a compound semiconductor thin film and a temperature drop rate.

FIG. 2 is a schematic view showing one example of a thin film forming apparatus of the present invention.

FIG. 3 is a process chart showing an example of a method for producing a compound semiconductor thin film of the present invention.

FIG. 4 is a cross-sectional view showing an example of the solar cell of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thin film forming apparatus 14 Evaporation source (element supply means) 15 Heater (heating means) 16 Radiation thermometer (temperature measuring means) 17, 23 Substrate 24 Thin film 25, 26 Compound semiconductor thin film 30 Solar cell 33 p-type compound semiconductor thin film (light Absorption layer)

Claims (13)

[Claims] 1. A method for producing a compound semiconductor thin film including a group I element, a group III element, and a group VI element, comprising: supplying the group I element, the group III element, and the group VI element onto a substrate. A thin film forming step of forming the compound semiconductor thin film on the substrate, wherein the compound semiconductor thin film is formed by utilizing the fact that the compound semiconductor thin film has a different temperature change rate depending on the composition of the compound semiconductor thin film during the thin film forming step. A method for producing a compound semiconductor thin film, comprising controlling the composition of the thin film. 2. A method for producing a compound semiconductor thin film containing a group I element, a group III element, and a group VI element, comprising: supplying the group I element, the group III element, and the group VI element onto a substrate. A thin film forming step of forming the compound semiconductor thin film on the base, wherein the compound semiconductor thin film is formed using at least one temperature change rate selected from the base and the compound semiconductor thin film during the thin film forming step. A method for producing a compound semiconductor thin film, comprising controlling the composition. 3. Prior to the thin film forming step, a ratio between the number of atoms of the group I element in the compound semiconductor thin film and the number of atoms of the group III element in the compound semiconductor thin film; 3. The method of manufacturing a compound semiconductor thin film according to claim 1, further comprising a step of determining the relationship of: 3, wherein the control of the composition of the compound semiconductor thin film is performed using the relationship. 4. 4. The method for producing a compound semiconductor thin film according to claim 1, wherein the temperature change rate is a temperature drop rate when the compound semiconductor thin film is cooled. 5. The method of forming a first thin film on a substrate by supplying the group III element and the group VI element onto the substrate,
A second step of forming a second thin film on the substrate by supplying an element containing at least the group I element and the group VI element onto the first thin film; A third step of supplying the element onto the second thin film until the temperature drop rate becomes at least equal to or less than a threshold value. 6. The first thin film forming step of forming a first thin film on the substrate by supplying the group III element and the group VI element onto the substrate.
And supplying an element containing at least the group I element and the group VI element onto the first thin film until the temperature drop rate becomes greater than a threshold value.
5. The method according to claim 4, further comprising: a second step of forming a thin film; and a third step of supplying at least the group VI element onto the second thin film until the temperature drop rate becomes at least a threshold value or less. The method for producing a compound semiconductor thin film as described above. 7. The temperature drop rate when the number of atoms of the group I element contained in the compound semiconductor thin film is substantially equal to the number of atoms of the group III element contained in the compound semiconductor thin film. Item 7. The method for producing a compound semiconductor thin film according to item 5 or 6. 8. The method for producing a compound semiconductor thin film according to claim 1, wherein in the thin film forming step, the temperature of the base is 250 ° C. or more and 600 ° C. or less. 9. The group I element is Cu, the group III element is at least one element selected from In and Ga, and the group VI element is at least one element selected from Se and S. Item 8. The method for producing a compound semiconductor thin film according to any one of Items 1 to 7. 10. A method for determining the composition of a compound semiconductor thin film containing a group I element, a group III element, and a group VI element, wherein a temperature change rate of the compound semiconductor thin film varies depending on the composition of the compound semiconductor thin film. And determining the composition of the compound semiconductor thin film. 11. A thin film forming apparatus for forming a compound semiconductor thin film containing a group I element, a group III element, and a group VI element on a substrate, wherein: a heating means for heating the substrate; Element supply means for supplying the group III element and the group VI element onto the substrate; and the substrate for judging a composition of the compound semiconductor thin film formed on the substrate by the element supply means. And a temperature measuring means for measuring at least one temperature selected from the compound semiconductor thin films. 12. A storage means for storing a relationship between a composition of the compound semiconductor thin film and a temperature change rate of the compound semiconductor thin film, and the compound semiconductor thin film using a temperature measured by the temperature measuring means and the relationship. 12. The thin film forming apparatus according to claim 11, further comprising: a determination unit configured to determine a composition of the thin film. 13. A solar cell having a light absorbing layer, wherein the light absorbing layer is made of a compound semiconductor thin film manufactured by the method of manufacturing a compound semiconductor thin film according to claim 1. Solar cells.