Hot-electron Phototransistors in Hydrogenated Amorphous Silicon

ABSTRACTIt has been shown that useful current gains can be obtained in hot-electron device structures containing very thin chromium disilicide layers of nanometer dimensions in hydrogenated amorphous silicon [1]. The a-Si:H/a-CrSi2/a-Si:H device structure made using PECVD and sputtering techniques naturally forms a hot-electron transistor device where the electrons are emitted across a high potential barrier on one side of the silicide and are collected over a low barrier on the other. Recent results [2] have shown that current gains can be in excess of 40 in structures having a-CrSi2 bases ∼1 nm thick.Here we outline the relatively simple technology used to make these devices and examine their performance as phototransistors in which the photo-current is amplified by hot-electron transistor action. The speed of response can be maximised by operating the phototransistor with high electric field across the collector since it is the transit time of the photo-induced carriers that determines the response time. We show that these devices provide a useful new active element for large area amorphous silicon electronics.