JPH058593B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of manufacturing a photoconductive element used as a visible range optical sensor for a facsimile machine or a reading line sensor for various office equipment. Conventional configurations and their problems Conventionally, optical sensors based mainly on CdS and CdSe have large photocurrents, especially when using CdS, a solid solution of this type of compound.
-CdSe-based optical sensors have sensitivity that covers the entire visible light range, so they have attracted attention and have been developed for applications such as contact-type line sensors in facsimiles. A typical manufacturing method for this CdS-CdSe optical sensor is as follows. That is, CdS− is placed on a suitable substrate.
A thin film of CdSe solid solution is formed by vapor deposition, and a CdS:CdCl ₂ (mixed, sintered, and pulverized) powder as an evaporation source of CdCl ₂ is placed together with the thin film in a semi-closed container made of alumina or the like and heated to a high temperature of about 500°C. evaporated by heating to
Crystals are grown in CdCl ₂ vapor, and at the same time sensitizing centers are formed to obtain a large photocurrent (this process is called activation). If the above manufacturing method is used, the dark current is quite large, so when depositing the CdS-CdSe thin film, Cu is used as an evaporation source at the same time, for example, CdS _1-x.
Se _x : If CuCl ₂ is mixed in the form of CuCl 2 (0x1; CdS, CdSe, and CuCl ₂ mixed, sintered, and crushed) and added to the deposited film, the dark current can be greatly reduced. be able to. Now, activation by CdCl ₂ vapor forms sensitizing centers, lengthens the lifetime of photoelectrons, and as a result, it is possible to obtain a large photocurrent, but basically the lifetime of photoelectrons corresponds to the photoresponse time. If the photocurrent is large, the response time will be long. Furthermore, such a polycrystalline thin film has a large number of trapping centers, so it has a major drawback in that the photoresponse time is much longer than the above-mentioned lifetime of photoelectrons at low illuminance. 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 is mainly composed of CdS, CdSe, or a solid solution of these two types of compounds, CdS-CdSe.
A thin film containing a small amount of Cu is then formed on the substrate.
The thin film is placed in a semi-closed container together with a CdCl ₂ evaporation source, and the thin film is exposed to CdCl ₂ vapor at high temperature to activate it along with crystal growth, forming an electrode, and then heat-treated in vacuum and in the dark. A method of manufacturing a photoconductive element is characterized in that: Description of Examples The thickness of the thin film is 2000-10000 Å, and the temperature of crystal growth is 450-600°C. The temperature during vacuum treatment is preferably 120 to 200°C. This is because if it is below 120℃, it will take too long for it to be effective, and if it is above 200℃, the changes will be too large and control will be difficult. The time for heat treatment in vacuum is preferably 0.25 to 4 hours. If it is less than 0.25 hours, it is difficult to obtain an effect, and if it is more than 4 hours, the photocurrent decreases significantly during the change. 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 when the amount is less than 10 lux. Hereinafter, specific examples of the present invention will be described.
The figure shows a cross section of a 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 the boat lid.
is CdS: _CdCl2 powder. Glass substrate (Corning 7059, 230 x 50 x 1.2
CdS _0.6 Se _0.4 : CuCl ₂ as evaporation source
It was deposited to a thickness of 4000 Å. Contained in the deposited film
The amount of Cu was 0.008 mol%. As shown in the figure, this substrate 3 is placed in an alumina boat 1 facing upward, and CdS:CdCl ₂ (2 mol%) powder 4 is placed in the longitudinal direction at a ratio of 0.2 g/cm at the center bottom of the boat.
and heated at 500°C for 1 hour. After forming NiCr/Au electrodes (width: 2 mm, gap: 1 mm) on the film obtained in this way, 0.25, 0.5
Heat treatment was performed for 1, 2 and 4 hours. DC10V was applied to the photoconductive element obtained in this way, and 100 lux green light (wavelength 555nm) was irradiated (flashing at 1Hz, 0.5sec increments) to increase the photocurrent J _p and its rise time τ _r (from 0 to saturation). (time to rise to 90% of the value), fall time τ _d (time to fall 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.

[Table] Effects of the Invention As described above, by performing the heat treatment in vacuum in the dark after forming the electrode, the rise time and fall time of the photocurrent can be significantly shortened while the photocurrent remains large. By using this optical sensor, it is possible to create a high-speed contact image sensor that uses a large current and has easy signal processing, and its industrial value is great.

[Brief explanation of the drawing]

The figure is a cross-sectional view of an alumina boat. 1...Boat body, 2...Boat lid, 3...
Glass substrate, 4...CdS: _CdCl2 powder.

Claims (1)

[Claims] 1. A thin film mainly composed of CdS, CdSe, or a solid solution of these two compounds, CdS-CdSe, containing a trace amount of Cu, is formed on a substrate, and the thin film is soaked in CdCl ₂ vapor. 1. A method for manufacturing a photoconductive element, which comprises heating the photoconductive element in a vacuum to activate it along with crystal growth, forming an electrode, and then heating in a vacuum and in the dark. 2. The method for manufacturing a photoconductive element according to claim 1, wherein the temperature of the heat treatment in vacuum is 120 to 200°C. 3. The method for manufacturing a photoconductive element according to claim 1 or 2, wherein the heat treatment time in vacuum is 0.25 to 4 hours. 4 Claim 1, characterized in that the degree of vacuum during heat treatment in vacuum is set at 0.01 atm as an upper limit.
A method for manufacturing a photoconductive element according to any one of items 1 to 3. 5. The method for manufacturing a photoconductive element according to any one of claims 1 to 4, characterized in that the illuminance during the heat treatment in vacuum and in the dark is 10 lux as an upper limit.