Thin film diamond photodetectors are one of the most promising classes of d
iamond devices for commercial exploitation. Already, photoconductive device
s which display extremely high levels of selectivity between deep UV and vi
sible light, allied to good sensitivity, are becoming available. However, m
ore advanced device designs are required if high speed operation is to be a
chieved alongside high sensitivity. Phototransistors are ideally suited to
this application, but until recently room temperature operation of diamond
field effect transistors (FETs) was not possible. This has changed with the
emergence of p-type hydrogenated diamond and this paper describes the fabr
ication and operation of the first MESFET based diamond photodetectors (OPF
ETs) to be made. Optical modulation has been demonstrated and the wavelengt
h selectivity measured. Devices respond significantly more to UV light than
visible wavelengths, with gain levels of around 4. The mechanism(s) of ope
ration are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.