Amorphous selenium (a-Se) avalanche photosensor with metal electrodes

Avalanche amorphous selenium (a-Se) photosensors have to withstand high electric field required for avalanche multiplication without degradation and dielectric breakdown. However, it is a technological challenge to avoid possible dielectric breakdown at the edges of metal contacts where the electric field experiences local enhancement. Our approach to improve stability against breakdown in avalanche a-Se structures with pixelated electrode array is to use a resistive interface layer (RIL) deposited between a-Se and the metal electrodes. By detailed analysis of charge transport properties we demonstrate that RIL enables stable avalanche operation in a-Se photoconductor without degradation in charge transport or avalanche multiplication gain. Our results show that a stable gain of 200 is reached at 104 V/μm for a 15 μm thick a-Se layer, which is the maximum theoretical gain for this thickness. We conclude that RIL is an enabling technology for practical implementation of solid-state avalanche a-Se image sensors.