Highly photosensitive transistors in single-crystal silicon thin films on fused silica

Abstract

Exceptionally high photosensitivity has been obtained in metal-oxide-semiconductor field-effect transistors fabricated in single-crystal silicon thin films on fused silica. The silicon films were laser crystallized and used to fabricate depletion mode transistors. Operating in pinch-off these buried-channel devices display an optical responsivity of ≳ 300 A/W of incident visible radiation. This is some four orders of magnitude greater than that achieved in enhancement mode devices of comparable design and processing. The basic mechanism for the high sensitivity is the spatial separation of photogenerated electrons and holes which results in long carrier lifetimes, as indicated by optical gains >103 and photocurrent decay times of the order of 10 μs.