We report a new structure of high-responsivity photodetectors
that utilizes the transparent and metallic zinc oxide
(ZnO) gate in bulk silicon metal–oxide–semiconductor field-effecttransistor
photodetectors. The device has a small optical window
only in the channel region, and all other regions (depletion) are
protected from external light. Whereas the amplification of photocurrent
by external light was not significant at the floated or
positively biased substrate, the photocurrent was enhanced at the
grounded or negatively biased substrate due to the decrement of
the recombination rate in the n-channel MOSFET. Responsivity
was in excess of 1500 A/W under white-light illumination, which
is higher than that of conventional photodetectors with the semitransparent
polycrystalline-silicon gate.