Patent ID: 7759698

Claim:
A compound semiconductor-based photo-FET comprising: a substrate; a channel layer that constitutes a current path between a source electrode and a drain electrode and serves as part of a photodiode and as part of a photosensitive region; a back-gate layer disposed between the substrate and the channel layer, forming a homojunction or a heterojunction relative to the channel layer, elongating a substrate-side depletion layer from the substrate toward the channel layer, applying to the channel layer a back-gate bias by photogenerated carriers upon light illumination, and serving as a substrate-side depletion layer formation layer; a barrier layer disposed on a the front side of the channel layer, having a wider bandgap than the channel layer, causing one of the photogenerated carriers to run through the channel layer and the other of the photogenerated carriers to sojourn or be blocked off; and a front-side depletion layer formation layer disposed on the front side of the channel layer, elongating a front-side depletion layer from a front side thereof towards the channel layer, bringing the front-side depletion layer into contact with the substrate-side depletion layer without illumination to close the current path in the channel layer, thereby bringing the photo-FET to an off-state.