A phototransistor fabricated from thin-film diamond is reported. Polycrysta
lline diamond grown by chemical vapor deposition, which is a-type by virtue
of near-surface hydrogen, has been used to realize optically activated met
al-semiconductor held-effect transistors (FETs). Devices with thin (30 nm)
Al Schottky gates and Au source and drain contacts operate as effective enh
ancement-mode metal-semiconductor field-effect transistors at room temperat
ure; illumination of an electrically isolated gate leads to increased chann
el current, although saturation is still evident. At deep UV wavelengths (<
220 nm), a photodetector gain of around 4 has been,measured; the mechanism
of operation has been identified as photodiode-like turn-on followed by FET
amplification. (C) 1999 American Institute of Physics. [S0003-6951(99)0290
2-2].