JPS6050075B2 - Activation method of photoconductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an activation method for increasing the photosensitivity of a photoconductive film. This relates to a method of adding a halogen element as a donor impurity and simultaneously improving the crystallinity of the film in order to increase the photosensitivity of the -1 group thin film.

INDUSTRIAL APPLICABILITY The present invention can be effectively used to improve the photoconductivity, that is, to increase the sensitivity and lower the resistance, of thin films of Π-■ group compound semiconductors produced by chemical deposition, vapor deposition, chemical spraying, sputtering, etc. However, the present invention generally provides ■-
Since it is possible to easily improve or adjust the crystallinity, electrical properties, and photoelectric properties of Group III compound semiconductor thin films with good reproducibility, it is also extremely useful in the production of photovoltaic thin films and luminescent thin films. .

Conventionally, methods for activating photoconductive films include a method in which the film to be activated is covered with the same activated powder and heat treated, and a method described in Japanese Patent Publication Showa submitted by Ross R. Chamberlin et al. 42-17865, a sintered film of activated matrix powder is deposited on the upper inner surface of a five-sided ceramic shroud, overlying the activated thin film and raising the temperature. There is a method of doping active impurities into a thin film to be activated by evaporating a sintered film of activated host powder.

The former method not only requires time and effort to produce the activated powder, but also has drawbacks such as uneconomical use of the activated powder and adhesion of the activated powder to the thin film. In the latter case, it is of course necessary to prepare the activated powder in advance, but it is not only difficult to apply the powder to the inner surface of the ceramic cover as a sintered film, but also With regard to one of the objectives, which is to reduce the resistance of thin films, these methods have been able to reduce the resistance only to a modest degree at most. In addition, when activation is performed using an activated powder or a sintered film to which both donor and acceptor impurities are added as in the conventional method, the donor and acceptor doped into the activated film by a curtain phase reaction. It is difficult to arbitrarily control the amount of impurity, and in particular, the addition of acceptor is more difficult due to the difference in vapor pressure between donor impurity and acceptor impurity, which poses a problem in terms of reproducibility. The present invention solves these drawbacks at once and provides a method for easily obtaining a photoconductive thin film with excellent photoconductive properties with good reproducibility, and is therefore very useful industrially.

That is, in the method of the present invention, the process of doping an impurity important for activating a photoconductive thin film is carried out in two steps. For example, in the case of a CdS thin film, steel or silver is doped at the same time as the thin film is formed, and then donor impurities necessary to improve the photoconductive properties of the photoconductive thin film, such as chlorine, are doped. It is doped with a halogen element such as halogen compound or iodine, and the same sintered film is sintered with a halogen compound added as a flux in an airtight or semi-airtight container with a limited internal volume.
It is a method in which a halogen element is doped by heat treatment at a high temperature for a certain period of time, and a photoconductive film with poor photoconductive properties can be obtained by appropriately adjusting it with a pre-doped acceptor impurity. According to this method, since the acceptor impurity is added in advance, the amount added can be controlled accurately and with good reproducibility, and there is no need to prepare the activated powder in advance, which is time-consuming as described in the conventional example. The sintered film is simply coated on a heat-resistant substrate with a mixture of the same powder as the thin film to be activated and a fluxing halogen compound that acts as a donor impurity, and then fired. You only need to use it. In addition, the photoconductive thin film activated by this method not only has extremely high photosensitivity, but also has a reduction rate of bright resistance that is less than that of the d-bath, making it possible to further reduce the bright resistance compared to conventional methods. ．． -The fact that it is possible has enormous industrial value. Examples of the present invention will be described below. EXAMPLE 1 This embodiment of the present invention describes a method for activating a CdS chemically deposited thin film deposited on a glass substrate as a group ■-■ photoconductive thin film by a chemical deposition method.

The method for manufacturing compound thin films and the method for adding acceptor impurities to these films in advance are based on the method described in Japanese Patent Publication No. 7376/1983, which was previously invented by the inventors.

The CdS thin film used in this example was prepared using a cadmium ion aqueous solution containing a trace amount of copper ions and a thiourea aqueous solution.
C precipitated on a glass substrate by reacting at 0°C and atmospheric pressure
dS. ．． It is a Cu chemically deposited thin film, more precisely, it is a thin film in which copper is co-deposited in the form of CuS in a CdSj deposited thin film. First, a 20x20x0.8 glass substrate placed on a substrate support was immersed in a reaction solution having the following solution composition, and the reaction solution was gradually raised from room temperature to 100°C at atmospheric pressure. Two particles are deposited while rotating the substrate. The thickness of the CdS/Cu deposited film thus deposited on the glass substrate is approximately 3000 Å.

Next, C deposited on a glass substrate 1 as shown in FIG.
The dS-Cu precipitated thin film 2 was placed in a square board 3 with an inner diameter of 20 and 27 WL, and CdS powder having a purity of 99.99% or more and 10q for 100y of this CdS powder were placed.
CdSI:. After thoroughly mixing and stirring the CdCl powder, 25×25×17177! The activated CdS- Heat treatment is performed at 500° C. for 20 minutes in an electric furnace in an inert gas atmosphere with a limited space between the Cu thin film and the CdS sintered film in a sealed or semi-closed state. After that, to investigate the photoconductive properties, the effective length is 5−, the electrode spacing is 0.
．． 15 using an incandescent bulb light source with two garlic facing comb-shaped electrodes
0L. L] Bright resistance, dark resistance, photosensitivity under X irradiation,
and the rate of decrease in light resistance. The results are as follows. As shown in the above table, the photosensitivity ratio of the activated CdS thin film was more than 103 times, and the reduction rate of bright resistance was very small, less than 11,500. This is because CUS(7)CU++, which was added in advance to the CdS thin film by performing the heat treatment as in the present invention, is
It becomes u+ and replaces CdS(7)Cd and enters the lattice to form an acceptor level.At the same time, C1 evaporated from the CdS sintered film replaces CdS(7)S and forms a donor level in the lattice. Furthermore, the CdS sintered film generates carbon in the thin film due to trace amounts of Cd and S vapor generated from the CdS sintered film.
This is because defects such as d and S are filled appropriately, and crystal growth necessary for increasing photosensitivity and lowering the resistance of a thin film can be sufficiently performed. Curve 6 in FIG. 2 shows the activated Cd in the above example.
In the spectral sensitivity curve of the S photoconductive thin film, a characteristic photoconductive element was obtained in which the sensitivity at wavelengths of 500 TrLμ or more was extremely low despite the addition of copper. Example 2 In this example, the results of activating a CdS thin film to which Ag is added as an acceptor impurity in advance will be described.

That is, when depositing a CdS thin film on a glass substrate in Example 1, 0.01 mol of Ag+ was used instead of Cu++.
A deposited film was prepared using the above reaction solution by adding 0.6 mL of NO3 aqueous solution. As a result of activation using the same method as in Example 1, the photosensitivity ratio was as large as 1 Cf' or more, and the bright resistance was also higher than that of the one that was not activated. A small piece was obtained, smaller than pickle. As shown by curve 7 in FIG. 2, a CdS photoconductive thin film was obtained which had a spectral sensitivity curve with lower sensitivity on the long wavelength side than that with copper added. Example 3 In this example, the results of activation by changing the amount of copper added in advance to a CdS chemically deposited film will be described.

In detail, Cu+ in the CdS precipitated film reaction solution of Example 1
The CdS-CuS precipitated film, which was deposited with the concentration of + varied between 0.1 and 1.0 mol% relative to Cd++, was activated under the same heat treatment conditions as in Example 1. As a result, the third
As shown in the figure, when heat treatment is not performed, the photosensitivity ratio is small and the bright resistance is large, as shown by the bright resistance of curve 8 and the dark resistance of curve 9 in Figure 3, but when heat treatment is performed as in the present invention, the photosensitivity ratio is small and the bright resistance is large. When this is done, the bright resistance increases as the amount of Cu increases as shown by curve 10, but the optimum addition amount of Cu is 0.3 mol%.
, the dark resistance of curve 11 shows the maximum value, and the photosensitivity ratio is 1.
A CdS thin film with excellent photoconductive properties was obtained, in which the photoresistance decreased by more than Cf and the rate of decrease in bright resistance was much smaller than that without heat treatment. Example 4 Next, in order to find the optimum temperature for heat treatment according to the present invention, the temperature was changed to 140015001 in the same manner as in Example 1.
As a result of performing heat treatment at 600° C., characteristics as shown in FIG. 4 were obtained.

In FIG. 4, curve 12 shows the bright resistance ρ in comparison with that without treatment, and curve 13 shows the dark resistance ρD at that time. The heat treatment conditions for obtaining an excellent CdS thin film are 50
It was found that 0°C is appropriate. In other words, in heat treatment at 400°C, an amount of C1 sufficient to compensate for Cu, which is an acceptor impurity doped in advance, is not released from the CdS sintered film; Since the heat treatment is not carried out sufficiently, the resulting film has a small photosensitivity ratio and almost no change in bright resistance, so it is considered that the heat treatment temperature is too low. On the other hand, at 600°C, more Cl is released from the CdS sintered film, causing cracks to occur at the extreme parts of the CdS thin film, and when such a film is attached with an opposing electrode, the resistance tends to increase. show. From the above results, it has been found that 500°C is the optimum temperature for the heat treatment of the present invention, as a temperature to appropriately adjust acceptor and donor impurities, and as a temperature to allow crystal growth of the thin film to be activated. Ivy. As shown in the above examples, in the present invention, the process of introducing acceptor impurities added in advance is carried out simultaneously with the formation of a thin film with a regular composition, and the work and equipment are simple, and the process can be performed accurately and reproducibly. Although it is effective when using a chemically deposited thin film by a chemical deposition method, vapor deposited films, chemically sprayed films, or sputtered films can also be produced by co-evaporation, co-spraying, or co-sputtering, or by using an aqueous solution after film formation. Since it is possible to introduce acceptor impurities through the substitution reaction, it is fully applicable to these films.

In addition, unlike conventional activation methods, it is possible to achieve a high photosensitivity ratio with relatively simple work without the need for labor-intensive work such as manufacturing activated powder or making the activated powder a more uniform and thick film. Since a thin film with low resistance and excellent photoconductive properties can be obtained with good reproducibility, it can be used as a photoconductive element suitable for use as a light receiving element for automatic exposure meters such as cameras, punch card readers, and pattern recognition sensors. Since it can provide a group of photoconductive elements, it is of extremely great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the positional relationship between a sintered film doped with donor impurities for activation of the present invention and a thin film to be activated that previously contains acceptor impurities, and FIG. Figure 3 shows the spectral sensitivity curve of the CdS photoconductive thin film activated in Example 3, in which the concentration of Cu++ was deposited with respect to Cd++ in Example 3, and the CdS thin film was untreated and activated according to the present invention. FIG. 4 is a graph showing the relationship between the Cu++ concentration and bright resistance and dark resistance in Example 4. FIG. 1...Glass substrate, 2...CdS chemically deposited thin film containing acceptor impurities, 3...Alumina board, 4...Alumina substrate, 5...・
...CdS sintered film containing donor impurities.

Claims (1)

[Claims] 1. Activation to impart photoconductivity to a II-VI compound semiconductor film previously deposited as a thin film by any of the following thin film forming methods: chemical deposition, vacuum evaporation, chemical spray, or sputtering. In the method described above, only acceptor impurities are added to the semiconductor film in advance, and then the same powder as the semiconductor film is sintered with a sintered body using a halogen compound as a flux. A method for activating a photoconductive film, comprising heating the semiconductor film at a predetermined temperature and time in an airtight container to activate the semiconductor film.