ac photoresponse of a large-area imaging CdS/CdTe heterojunction

Experimental data are presented for the photosensor-substrate structure presently used with the ac liquid-crystal projection light valve. This structure consists of a thin film (sputter deposited) of n-type CdS on which is evaporated a thin film of p-type CdTe. In an earlier publication, a model was presented which describes the photosensitivity of this structure in terms of the depletion-width photocapacity of the charge-storage diode formed by these two coatings. The experimental data presented here correlate well with this model. Among the data presented are data on light-valve display, photosensor gray scale, and response time. The response-time data are of particular interest because they show that the projection-light-valve photosensor is capable of operation at near-TV rates. The agreement of the experimental data with model and extrapolation from the model imply that large improvements in sensitivity and response time are still quite possible.