A high-sensitivity silicon-on-insulator (SOI) metal-oxide-silicon (MOS
) photodetector compatible with conventional silicon technology is pro
posed. Its operation principle is based on that of a lateral bipolar t
ransistor in spite of an SOI MOS device structure. Photodetectors with
narrow base width or short channel length have high current gain whic
h is attributed to a self-biased effect under illumination. Current ga
in as high as 100 has been achieved for the device with a channel leng
th of 1.0 mu m. Measured intrinsic response time for optical pulses is
19 mu s for the photodetector with a channel length of 0.7 mu m.