JPH0133955B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a photoconductive thin film used as a visible range optical sensor. Conventional configurations and their problems Conventional optical sensors based on CdS and CdSe have large photocurrents, so optical sensors based on CdS-CdSe, a solid solution of these two compounds, cover the entire visible light range. Due to its high sensitivity, it has been attracting attention and being developed as a contact-type line sensor for facsimile machines. 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 the evaporation source at the same time, for example, CdS _1-x.
Se _x : If Cu 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 significantly reduced. can. 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. In addition, the adhesion strength of the electrode is weak due to the residual adhesion of CdCl ₂ on the surface of the thin film, the dark current is large, the reproducibility of characteristics is poor, and there are large spatial variations. Purpose of the Invention The present invention has stronger electrode adhesion strength, lower dark current, and lower dark current than photoconductive thin films manufactured using conventional methods.
Provided is a method for manufacturing a photoconductive thin film that has a short photocurrent response time, excellent reproducibility of characteristics, and small variations. Structure of the Invention The present invention forms a thin film mainly composed of CdS, CdSe or CdS-CdSe solid solution on a substrate,
When manufacturing a photoconductive thin film by placing the thin film together with CdCl ₂ powder in a semi-closed container and exposing the thin film to CdCl ₂ vapor at high temperature to activate it along with crystal growth, electrode formation is performed. This is a method for producing a photoconductive thin film, which is characterized by washing the thin film with water before washing. Description of Examples The thickness of the thin film is preferably 2000-10000 Å. If it is less than 2000 Å, there will be effects such as a slight decrease in film thickness during the crystal growth stage, and the photocurrent J _p will become smaller, and its rise time τ _r will conversely become larger.
This is because when it is 10,000 Å or more, J _p tends to be large and its fall time τ _d tends to become long. The crystal growth temperature is preferably 450 to 600°C. If it is below 450℃
Crystal growth is difficult to occur due to insufficient vapor pressure of CdCl ₂ ,
On the other hand, at temperatures above 600°C, the vapor pressure of CdCl ₂ is too high and crystal growth is promoted too much, resulting in pinholes. The temperature during the water washing treatment may be room temperature, but is more preferably 40 to 80°C. This is because if it is below 40°C, it will take time to obtain the effect, and if it is above 80°C, the thin film may peel off. If ultrasonic waves are used in conjunction with water washing, the process can be completed in a short time. This water washing process significantly reduces the dark current J _d of the optical sensor, stabilizes the characteristics (J _p , τ _r , τ _d ), and speeds up the response (τ _r , τ _d ). Hereinafter, the effects of the present invention will be explained using examples. Example Glass substrate (Corning 7059, 230×50×1.2
mm ³ ), CdS _0.6 Se _0.4 :CuCl ₂ (0.2 mol %) was evaporated to a thickness of about 4000 Å using an evaporation source. The amount of Cu contained in the deposited film was 0.008 mol%. As shown in the figure, the alumina board body 1 (upper lid 2
CdS:CdCl ₂ (2 mol %) powder was placed in the length direction at a ratio of 0.2 g/cm at the center bottom of a rectangular parallelepiped with an internal volume of 52 x 310 x 20 mm ³ , and the above vapor deposited film was provided on top of the glass. Place the substrate 3 facing upward, leave a gap of 2 mm with the lid 2, cover with the lid, and heat. Heated at 500°C for 1 hour. The membrane thus obtained was taken out from the boat and further heated to 20, 40, 60 and 80°C.
After washing in water for 2 minutes with ultrasonic waves and drying
NiCr/Au electrodes were formed by vapor deposition (width 2 mm, gap 1 mm). DC10V is applied to the optical sensor obtained in this way.
Apply 100 lux of green light (wavelength 555nm)
was irradiated (at 1 Hz, 0.5 seconds each), and J _p , its τ _r (time to rise from 0 to 90% of the saturation value), and τ _d (time to fall from the saturation value to 10%) were measured. The results are listed in the table along with the results without water washing.

[Table] In addition, untreated electrodes may peel off in the tape peel test, but those that have been washed with water do not. Effects of the invention As can be seen in the table, this water washing treatment not only increases the adhesion strength of the electrode, but also significantly reduces the dark current, and speeds up the photocurrent response characteristics (rise time, fall time). The reproducibility is excellent and the variation is small.

[Brief explanation of drawings]

The figure is a sectional view of a board used in the present invention. 1...Board body, 2...Board 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 types of compounds, CdS-CdSe, containing a trace amount of Cu, is formed on a substrate, and the thin film is soaked in CdCl ₂ vapor. Production of a photoconductive thin film, which is characterized in that the thin film is washed with water before forming the electrodes, after being activated with crystal growth through heat treatment at , and then forming electrodes to produce the photoconductive thin film. Method. 2. The photoconductive thin film according to claim 1, wherein the thin film has a thickness of 2000 to 10000 Å, a crystal growth temperature of 450 to 600°C, and a water washing temperature of 40 to 80°C. Production method.