Deep-Depletion Effect in SOI Substrates and its Application in Photodetectors With Tunable Responsivity and Detection Range

We present an interesting transient effect found in silicon-on-insulator (SOI) transistors, where the drain current responds slowly to a back-gate voltage ( ${V}_{\text {BG}}$ ) pulse. This transient mechanism is due to the deep-depletion region in the SOI substrate induced by the ${V}_{\text {BG}}$ pulse and has been validated by experimental and TCAD simulation results. The deep-depletion characteristic can be employed for photodetection in a fully depleted (FD)-SOI MOSFET device. We have measured the photoresponse of the FD-SOI MOSFET under various light illumination conditions and studied systematically the impact of the ${V}_{\text {BG}}$ pulse duty ratio, amplitude, and period on the responsivity and detection range. An optimized device structure, fabricated in an advanced ultrathin body and buried oxide (BOX) (UTBB) SOI technology, shows low operation voltage and extended detection range.