The role of the blocking structure in hydrogenated amorphous silicon vidicon targets

Vidicon targets based on hydrogenated amorphous silicon (a-Si:H) are investigated. The role of the blocking contact to the photoconductor is discussed and a series of the experiments on the photoconductive properties for various kinds of target structures (doping concentration, film thickness) are presented. Without the blocking layer, the device characteristics would suffer not only from the increased dark current level but also from the lower photocarrier transport due to the accumulation of trapped space charge which would distort the internal field. The blocking layer is essential in photoelectric imaging devices to prevent the carrier injection and to sustain the high field in the photogeneration region. The correlations between the device performances and the target structures are also discussed.