Blocking Contact Structure of the Photoconductive Target

If the electrodes for the photoconductive targets are ohmic-type contacts, the dark current is at least comparable to the value determined by the bulk resistivity of the a-Si H itself. In addition, carriers continue to flow into a-Si H even after the illumination is stopped, until the carriers trapped in a-Si H are neutralized. Thus, it is hard to obtain a low dark current and a high photoresponse. 

To avoid these problems, other types of blocking contacts have been proposed (Oda et al., 1981, Hatanaka et al., 1982 Ishioka et al., 1983). In these cases, a wide-gap transparent thin film such as SiOz or Si N,., is used as a hole-blocking layer in place of the n layer. A chalcogenide, such as Sb2S3 or As2Se1.5TeI.5, or an oxide such as Ce02 thin film, is then used instead of the p layer. 

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