JPS6184876A - Method for manufacturing photoconductive elements - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a photoconductive element used as a visible range optical sensor for a reading license sensor for facsimiles and various office automation equipment.

Structures of conventional examples and their problems Conventionally, optical sensors mainly composed of CdS or CdSe have a large charging current, especially when solid solutions of this type of compounds, Cd5-
Optical sensors based on CdSe have a sensitivity that covers the entire visible light range, and have therefore been attracting attention and being developed for applications such as close-contact line sensors in facsimiles.

A typical manufacturing method for this CdS-CdSe optical sensor is as follows. That is, CdS −
A thin film of CdS e solid solution is formed by evaporation, e.g. CdS : CdC12 (mixture,
The sintered and pulverized) powder is placed in a semi-closed container made of alumina or the like with the thin film, heated to a high temperature of about 500°C, and crystals are grown in the vapor of evaporated cacl, forming sensitized centers at the same time. This leads to obtaining a large photocurrent (this process is called activation). Since the dark current is quite large in the above manufacturing method (dS), when the -CdSe thin film is deposited, the evaporation source is used at the same time (for example, when u is CdS, -xSsx
: CuC1, (o<x<1; CdS, CdS
e.

If Cu is mixed into the deposited film in the form of mixed, sintered, and pulverized Curl 2, the dark current can be significantly reduced.

Now, activation by CdCl2 vapor forms sensitizing centers, lengthens the lifetime of photoelectrons, and as a result, it is possible to obtain a large photocurrent. However, basically, the lifetime of photoelectrons corresponds to the photoresponse time, so If the current is large, the response time will be long. Furthermore, such a polycrystalline thin film has a major drawback in that the photoresponse time is much longer than the above-mentioned lifetime of photoelectrons at low illuminance because of the large number of trapping centers.

OBJECTS OF THE INVENTION The present invention provides a method for manufacturing a photoconductive element whose photoresponse time is short without compromising the magnitude of the photocurrent.

Structure of the Invention The present invention consists of a solid solution of CdS, CdSe, or these two types of compounds (dS-CdSe as a product component), and a thin film containing a trace amount of - is formed on a substrate, and a thin film is formed on a substrate in a semi-hermetically sealed state together with an evaporation source of CdC12. A photoconductive element characterized in that the thin film is placed in a container and exposed to CdCl2 vapor at high temperature to activate it along with crystal growth to form an electrode, and then heat-treated in vacuum and in the dark. This is a manufacturing method.

Description of Examples The thickness of the thin film is 2000-10000, and the temperature of crystal growth is 450-600°C.

The temperature during vacuum treatment is preferably 120 to 200'C.

If the temperature is below 120'C, it will take too long to be effective.
This is because if the temperature exceeds 200°C, the changes will be too large and control will become difficult. The time for heat treatment in vacuum is 0.25 to 4
time is preferable. If it is less than 0.25 hours, it is difficult to obtain an effect, and if it is more than 4 hours, the change, especially the decrease in photocurrent, is significant. The degree of vacuum during the heat treatment in vacuum is effective over a wide range of degrees of vacuum, but it is preferably 0.01 atmosphere or less. If the pressure is above 0.01 atm, the effect may be small or it may take too long for a change to occur. Further, during the heat treatment in vacuum, it is preferable to perform the heat treatment in the dark; if it is bright, changes will be less likely to occur and the amount of change will be small. In particular, the effect is greater for 1Q lux or less.

Hereinafter, specific examples of the present invention will be described.

The figure shows a cross section of the boat used in the present invention, where 1 is the boat body, 2 is the boat lid, 3 is the glass substrate, and 4 is CdS:
It is CdCl2 powder.

Glass substrate (Corning 7059.230×50X
1.2 nest') on top of Cd5 (,65so4:
01101□ was evaporated to a thickness of approximately 4000 mm using the evaporation source. The amount of Cu contained in the deposited film is 0.
．． It was 0.008 mol%. As shown in the figure, place this board 3 in an alumina boat 1 facing upward and place it at the center bottom of the boat.
dS: 0.2 of CdC112 (2 mol%) powder 4
! Place it in the length direction at a ratio of y/cyn, cover it with a lid 2, and
Heated at 00°C for 1 hour. Membrane iCN obtained in this way
Vapor deposition formation of iCr/muU electrode (width 2 mm, gap 1
After removing the feathers), it is placed in a vacuum (0.01 atm) and in the dark (1
0 lux) and 0.25 and 0.5 at 175°C.

Heat treatment was performed for 1.2 and 4 hours. DClov was applied to the photoconductive element obtained in this way, and 100 lux green light (wavelength 555 nm) was irradiated (0.s sea at 1-) to increase the photocurrent J and its rise time τr (from o time until it reaches 9o% of the saturation value), fall time τd
(The time required for the saturation value to drop to 10% of the saturation value) was measured. The results are listed in the following table along with the results without such vacuum heat treatment.

(Margins below) Characteristic table (Jp, τ1.τ,) Effects of the invention As mentioned above, the photocurrent is large due to the heat treatment in vacuum in the dark after electrode formation, and its rise time is
Fall time can be significantly shortened. If this optical sensor is used, it will be possible to create a high-speed contact type image sensor with large current and easy signal processing, which has great industrial value.

[Brief explanation of the drawing]

The figure is a cross-sectional view of an alumina boat. 1-...Hoard body, 2...Boat lid,
3...Glass substrate, 4...CdS:
CdC1□ powder.

Claims (5)

[Claims] (1) A thin film mainly composed of CdS, CdSe, or a solid solution of these two types of compounds, CdS-CdSe, containing a trace amount of Cu is formed on a substrate, and the thin film is
A method for manufacturing a photoconductive element, which comprises heat-treating in Cl_2 vapor to activate crystal growth and forming electrodes, and then heat-treating in vacuum and in the dark. (2) Temperature of heat treatment in vacuum is 120-2000℃
A method for manufacturing a photoconductive element according to claim 1, characterized in that: (3) Claim 1 or 2, characterized in that the heat treatment time in vacuum is 0.25 to 4 hours.
A method for manufacturing a photoconductive element according to 2. (4) Claims 1 to 3, characterized in that the degree of vacuum during heat treatment in vacuum is 0.01 atmosphere or less.
A method for manufacturing a photoconductive element according to any one of paragraphs. (5) The method for manufacturing a photoconductive element according to any one of claims 1 to 4, characterized in that the illuminance during heat treatment in vacuum and in the dark is 10 lux or less.