JPH0316233A - Manufacture of photoconductive thin film - Google Patents

Abstract

PURPOSE:To improve photoresponse speed by specifying the atmosphere in case of heat-treating CdS, CdSe, or CdS/CdSe thin film in the atmosphere which contains CdCl2. CONSTITUTION:A film, which is mainly composed of CdS, CdSe, or CdS/CdSe containing a very small amount of Cu, is heat-treated in the atmosphere which contains CdCl2. The concentration of O2 in the atmosphere at this heat treatment is set to 20-60% (for the rest, N2). With the increase of O2 concentration, photocurrents Jp decrease, and according to that gamma4 decrease, but gammar does not increase and becomes almost fixed. Moreover, the rise time till Jp reaching 50% from O is defined as gammar, and the time till its decreasing to 50% from a saturated value is defined as gammad. What is more, if O3 concentration is 60% or more, Jp becomes too small, and circuit cost becomes high. Hereby, photoresponse speed can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a photoconductive thin film mainly composed of CdS, CdSe, or a solid solution of the above two substances (hereinafter abbreviated as CdS/Cd's). Regarding methods for producing photoconductive thin films aimed at improving response speed, conventional techniques are used to produce photoconductive thin films by heating a thin film mainly composed of CdS, CdSe, or CdS/CdSe in an appropriate atmosphere at high temperatures. It is already known that this thin film can be formed using chemical deposition, vacuum evaporation, sputtering, etc. to give photoconductivity to CdS, CdSe, or CdS/CdSe. Although it is common practice to add a small amount of a metal such as Cu, etc. and crystallize it under heating at a temperature of 500°C or higher, the photoconductive thin film obtained by this method is not one that is mainly composed of CdS. Although it is known that a film containing 4 to 0.8μ and CdSe is sensitive to longer wavelength light and at the same time shortens the response time, the introduction of C1 into the film lowers the crystallization temperature (de, crystal grains). C1 not only increases Cd, but also enters into the main precipitate and creates defects in the crystal.At the same time, Cd vacancies are created, which become sensitization centers and significantly increase the photocurrent (hereinafter referred to as J).However, C1
acts as a donor in the crystal, so at the same time dark current (J
．． ) becomes quite large. On the other hand, when Cu is introduced, donor electrons are consumed to compensate for Cu ions, so J
- can be made small. Therefore, in general, a method is adopted in which Cu is co-added with the introduction of C1 to increase Jp and reduce J4. Regarding the response time, the response time is as follows: Time rise time τ11 From saturation value 5
If the time for the decrease to 0% is τ-, then when the Cl concentration is high, the number of sensitized centers increases and the lifetime of the electrons becomes longer. Roughly speaking, this process involves forming a thin film of CdS, CdSe, or CdS/CdSe on an insulating substrate, and then heat-treating the thin film in an atmosphere containing C dC b vapor to increase photosensitivity. Cu is introduced as an impurity when forming a thin film.
Even if l is introduced during the heat treatment, the specific method is as described in detail in Japanese Patent Application Laid-open No. 17334/1984. ．． CdS or CdSe or CdS/C
A mixture of dSe and a small amount of CuCh is sintered at 700-1000°C and then crushed to serve as an evaporation source. This is formed into a thin film on a glass substrate by vacuum evaporation, and this thin film is heated to 500-600°C. Particles are grown by heat treatment in air for 10 to 60 minutes, and photosensitivity is obtained by introducing impurities into the lattice points.Problems that the invention aims to solveThe problems with conventional optical sensors are that Figure 4 shows the difference in optical response speed of optical sensors fabricated by the conventional manufacturing method by varying the Cu concentration in the film. Also shows the relationship between JD and response time.
In the practical area of current, the response speed is J. Related to LA J. As τ increases, τr decreases, or becomes exhausted due to the decrease τ−
On the other hand, as J- becomes smaller, τ increases and τ- decreases. Here, an example is shown. However, as mentioned above, τr and τ- are Since they are in a contradictory relationship, it is difficult to reduce the size of both of them. A film obtained by evaporating an evaporation source containing a trace amount of Cu on a substrate was heated to 500 to 60% in an atmosphere containing CdClg.
In the method for producing a photoconductive thin film obtained by heat treatment at 0°C for 10 to 60 minutes, the atmosphere is characterized in that the atmosphere is mainly composed of N2 and 02, and the content of 02 is 20% or more and 80X or less. In the production method of the present invention, the concentration of 02 in the atmosphere during heat treatment is set at 20 to 60%. is decreasing, and τ4 is decreasing accordingly. τ, is almost constant. In other words, as shown in Figure 1, τ- is decreasing as Js is increasing as the concentration is increasing. τP is not increasing. It is also possible to reduce τr by increasing the O concentration during heat treatment compared to the conventional manufacturing method performed in air (approximately 20% at 02!1 degrees). The OII concentration was set below 60% (above, J
, becomes too small, causing practical inconveniences such as increased circuit cost.However, in order to prepare the evaporation source of the example, 0.6 moles of CdS and 0.4 moles of lkcdse were mixed with 0.4 moles of CuC1* as an impurity. 00
Weigh out 2 mol of t and mix. Spread the mixture at 800°C for 1 hour in an inert gas. After cooling, pulverize and use this as an evaporation source by vacuum evaporation to form a glass substrate (#
7059 Corning, 40x 40x l. 1
) The substrate temperature is 15 Qt, and the film thickness is approximately 4,500 mm.Next, the film is patterned into strips using a photolithography and etching process. C added
One gram of dS powder in the form of a tablet is placed in a quartz bowl 1, covered with a lid, and the whole is placed in the quartz tube for heat treatment. The atmosphere at that time was a mixed gas of N2 and 02, and after the inside of the tube was evacuated, the gas was introduced and the heat treatment was carried out.
After the gas is filled, the temperature is maintained at ζ1 520t for 30 minutes.Then, the 02 concentration is set to 0 to 80%, and the pattern for removing the resist paste for the electrode shape is prepared. K N iC r
/Au (500/650A) is electron beam evaporated and lifted off to form a planar electrode.The size of the light receiving area is 55x90μ.Finally, this is heat treated in N2 at 250℃ for 30 minutes. .

The sensor characteristics were measured using an applied voltage of 10 V between the electrodes.
570 nc 100 lux light continuous illumination response time (this is done using IHz pulsed light). Show the relationship to Oe
As the concentration increases, J- decreases, and τ decreases accordingly. τP remains almost constant. Figure 3 shows the relationship between Je and response time of the photoconductive thin film produced by the manufacturing method of the present invention. It can be seen that as the force t Ol concentration increases and J- decreases, τ- decreases, and τr does not increase as seen in the optical sensor according to the conventional method shown in FIG. Depending on the method of manufacturing the photoconductive thin film,
L Compared to conventional methods, it is possible to obtain a photoconductive thin film with a faster response time, and its industrial value is enormous, as its use as terminals for various office automation equipment such as facsimiles is expanding.

[Brief explanation of drawings]

Claims (1)

[Claims] A film obtained by evaporating an evaporation source mainly composed of CdS or CdSe or a solid solution of the above two substances and containing a trace amount of Cu on a substrate is heated at 500 to 600 °C in an atmosphere containing CdCh at 10 to 60 °C. In the method for producing a photoconductive thin film obtained by heat treatment for a minute, the atmosphere is N_
2 and O_2 as main components, with an O_2 content of 20% or more,
60% or less.