High-speed CdS0.2Se0.8photoconductor and its application to line-image sensors

The photoelectric properties of CdS1-xSex(x = 0.4-1.0) photoconductor-type sensors were measured. The sensors were made by heat-treating an evaporated film under the influence of CdCl2vapor. The photocurrent Jpis large, and the dark current Jdis small; theS/Nratio derived from theJ_{p}/J_{d}ratio reaches a value of more than 60 dB. With increasingx, the decay time of the photocurrent decreases, while the rise time increases. By addition of continuous light bias, the rise time is drastically reduced. Furthermore, the decay time is reduced by increasing the applied voltage. These effects are pronounced for a CdS0.2Se0.8sensor. Using this sensor, we constructed a contact-type line-image sensor (8 bits/mm, 1728 bits), and attained a scanning rate of 1 ms/line and a total time of about 2 s for reading an ISO A4 size document. The reading was performed under an application of 20 V, and an illumination of 7.5-µW/cm²light bias and 15 µW/cm²(∼100 lux) signal light using LED light sources (570 nm).