JPS6323374A - Manufacture of photoconductive film - Google Patents

Abstract

PURPOSE:To manufacture an optical potentiometer high in dark resistance and light and darkness resistance ratio, and excellent in optical response, by introducing oxygen in the final stage of heat treatment process. CONSTITUTION:Oxygen is led in the final stage of heat treatment process to activate cadmium selenide formed on a heat resistant insulating substrate. For example, after forming a CdSe film on an aluminium substrate by vacuum evaporation ptocess, Cu evaporated thereon is put on a quartz boat comprising CdSe mixed with CdCl2 to be heated in N2 flow further supposed to be mixed with O2 three minutes before finishing the heat treatment process meeting the requirements for N2 flow rate of 0.1/min or O2 flow rate 0.3/min. Through these procedures, the light and darkness resistance ratio and the optical response of photoconductive film comprising CdSe can be improved by increasing the dark resistance.

Description

[Detailed Description of the Invention] [Summary] As a method for improving the photoresponsiveness and light-to-dark resistance ratio of an optical potentiometer, oxygen A method for producing a photoconductive film that introduces.

[Industrial application field]

The present invention relates to a method for producing a photoconductive film with improved photoresponsiveness and light-to-dark resistance ratio.

A photoelectric potentiometer is a non-contact type potentiometer, and is a photoelectric conversion element composed of a resistive film, a photoconductive film, and an electrode film.

The required potential is obtained by irradiation with a minute light spot, and the necessary conditions for this are that the photoconductive film has a large light-to-dark resistance ratio and has fast photoresponsiveness.

[Conventional technology]

Figure 2 is a plan view of a photoelectric potentiometer, in which a photoelectric film is formed to a thickness of about 1 μm on a heat-resistant insulating substrate such as alumina, and a resistive film and an electrode film are patterned on this. Element formation is underway.

Here, to describe an example of the element configuration, the thickness is 500 to 7
1 on both ends of a 00 μm Nichrome (NiCr) resistive film 1.
The base is a NiCr film with a thickness of about 1,000
Input electrode 2 and ground electrode 3 made of gold (Au) film
is provided with an input terminal 4 and a ground terminal 5, and an output electrode 6 is provided in parallel with a gap of about 50 μm from the resistive film 1 to the photoconductive film 8 as a base layer. An output terminal 7 is provided.

In operation, a voltage is applied between the input terminal 4 and the output terminal, and a light spot 9 is irradiated onto the photoconductive film 8 while a current i is flowing through the resistive film 1. The resistance decreases by several orders of magnitude, resulting in a state similar to if the resistive film 1 and the output electrode 6 were short-circuited at this position, and the potential of the resistive film l at that position appears at the output terminal 7.

In such a photoelectric potentiometer, the necessary conditions for the optical film 8 are as follows: ■ The dark resistance is several orders of magnitude higher than the resistance of the resistive film 1.
0 Ω or more; (1) the light-to-dark resistance ratio is sufficiently high; (2) the light response speed is fast, on the order of several 10 μs to several 100 μs.

etc.

Here, the materials for the photoelectric film used in photoelectric potentiometers include cadmium selenide (CdSe), cadmium sulfide (CdS), and cadmium selenide sulfide (CCd).
Compound semiconductors such as (SeS) are used.

However, such a compound semiconductor has many defects (vacancies) when it is formed by vacuum evaporation or sputtering, and cannot be used as a photoconductive film in that state.

For this purpose, activation treatment such as annealing is required.

Here, CciS and Cd (SeS) are used as compound semiconductors.
When using a compound semiconductor containing sulfur (S) such as sulfur (S), it is necessary to heat treat it at a temperature of around 650°C in an inert atmosphere, such as a nitrogen (N2) stream, in order to eliminate defects in the deposited film. However, in this case, the component elements, especially S and Se, evaporate at the same time, resulting in extremely poor controllability and reproducibility.

Therefore, we prepared an alumina substrate with a vapor-deposited film of CdS or Cd (SeS) in cadmium chloride (CdCl□) at 550°C.
A photoconductive film is produced by activating it by heat treatment at a temperature of about 0.degree.

However, even if one attempts to actually obtain photoconductivity through such activation treatment, there are too many defects (vacancies) involving S in the film made of CdS or Cd (SeS).
Therefore, although it has potential as a photoconductive film, the dark resistance is small, and therefore the light-dark resistance ratio does not become large.

Therefore, copper (Cu) is added to increase the resistance and improve photoconductivity.

As a method, a Cu film is formed to a thickness of several tens of layers by vapor deposition or the like on a photoconductive film obtained by vapor deposition or sputtering, and this is coated with CdCl! in an inert atmosphere such as N2. 2 and heat-treated to activate it.

However, in the case of CdSe, sulfide does not produce any defects in the heat treatment performed at around 550°C for activation, so the addition of Cu or the heat treatment in coexistence with CdCNZ is not necessarily a necessary treatment step. It wasn't.

[Problem that the invention seeks to solve]

The object of the present invention is to find an activation method that can increase the dark resistance of a photoconductive film made of CdSc, improve the light-to-dark resistance ratio, and improve the photoresponsiveness.

(Means for solving the problem) The above problem is caused by the fact that after coating a vapor-deposited film of CdSe formed on a heat-resistant insulating substrate, which is much thinner than the thickness of the film (Cu), it is deposited in an inert atmosphere. This can be achieved by a method for manufacturing a photoconductive film in which oxygen is introduced at the final stage of the heat treatment process in a process for manufacturing a photoconductive film in which CdSe is activated by heat treatment in the presence of CdCl 2 .

[Effect]

As a result of research on the activation of CdSe deposited films, the inventors found that in order to convert Cd5ei deposited films into photoconductive films, it is necessary to add Cu or CdCj! Although heat treatment in the presence of z is effective, the authors found and reported that the effect of oxygen is more significant.

Kusage, Yoda, Takojima, 1985 National Conference of the Institute of Electrical Communication Engineers of Japan, Lecture Proceedings Volume 1 2.289) The table shows the results of this experiment.
The two types shown in the table are prepared by vapor depositing u to a thickness of 13 mm, and these are CdSe and CdCf,
placed on a quartz boat containing
This is the result of heat treatment for 70 minutes.

However, the illuminance condition is 25βX in the bright state and 2.5 in the dark state.
j2x.

Here, at the final stage of the heat treatment, a process was also performed in which 0□ was introduced into N2.

The presence or absence of 02 in the second column indicates this.

From this table, it is clear that the effect of Cu addition is also recognized for CdSe, but the effect of the 0□ treatment is even more remarkable.

The present invention further develops this experimental result and applies it to an optical potentisimeter.

That is, the necessary conditions for a photoconductive film for an optical potentiometer are that it has a high dark resistance, a high light-to-dark resistance ratio, and a fast photoresponse speed.

In the present invention, the resistance of the photoconductive film is adjusted by the amount of Cu added.

As a result of experiments, the inventors found that there is a significant relationship between bright resistance and photoresponsiveness, and in this case, the influence of 0□ treatment is significant.In order to control the bright and dark resistance value, the amount of Cu added must be adjusted. I found out that I could control it.

Figures 1 (A) and (B) show the effects of the 0□ treatment;
It shows the relationship between bright resistance value and photoresponsiveness when the illuminance is 3000 lux (A'x).

In the figure, τ4. . represents the time it takes for the photocurrent to attenuate to 1/10 of its value when the light source is turned off, while τ2. .

When the light source is turned on, the photocurrent increases and reaches the saturation amount of 9710
It shows the time until

As is clear from this figure, the influence of the 02 process is significant, and as shown in figure (B), when forming a photoconductive film for an optical potentiometer by the conventional method, the minimum τ410 (falling time) is Lms. is the limit, but by using the method of the present invention, as is clear from the same figure (A), 0.
This can be shortened to about 2 ms, making high-speed tracking possible.

〔Example〕

Cd was deposited on an alumina substrate to a thickness of 1 μm by vacuum evaporation method.
After forming the Se film, prepare a film on which Cu is vapor-deposited to a thickness of 13 mm, place it on a quartz boat containing a mixture of CdSe and CdCl2 at a heavy equipment ratio of 100:5, and heat it with N2.
It was heated at 550° C. for 70 minutes in an air stream.

Note that 0 □ was mixed in the N2 gas flow from 3 minutes before the end of the heat treatment.

The conditions are that the flow rate of N2 is 1.01/min and the flow rate of 0□ is 0.347 min.

The bright resistance value of the photoconductive film thus prepared was 9×10 3 MΩ under 25 lux illumination, and a light-dark resistance ratio of 30 was obtained.

Also, as the photoresponsiveness (1111 value is 0.2ms
I was able to obtain the value of

〔Effect of the invention〕

As described above, by carrying out the present invention, it is possible to realize an optical potentiometer that has a higher dark resistance, a larger light-to-dark resistance ratio, and better photoresponsiveness than conventional ones.

[Brief explanation of the drawing]

Figure 1 is a diagram of the effects of heat treatment on photoresponsiveness, and Figure 2 is a plan view of a photoelectric potentiometer. In the figure, 1 is a resistive film, 2 is an input electrode, 3 is a ground electrode, 6 is an output electrode, 8 is a photoconductive film,
9 is a light spot.

Claims (1)

[Claims] A vapor-deposited or sputtered film of cadmium selenide formed on a heat-resistant insulating substrate is coated with copper much thinner than the film, and then heat-treated with cadmium chloride in an inert atmosphere to form the cadmium selenide. A method for producing a photoconductive film, characterized in that the process for producing a photoconductive film is carried out by introducing oxygen at the final stage of the heat treatment step.