Band-Edge Photoresponse Characteristics of Diamond MSM's
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BAND-EDGE PHOTORESPONSE CHARACTERISTICS OF DIAMOND MSM'S Mike Marchywka*, Steven C. Binari**, Deborah A. Koolbeck*, and Daniel Moses* *E.O. Hulburt Center for Space Research, "**Electronic Science and Technology Division Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375-5000 Internet: ccd@heliosl .nrl.navy.mil
ABSTRACT Band-edge photoresponse measurements on simple diamond metal-semiconductor-metal (MSM) devices can give information about the quality of the diamond material and its utility as a detector. We have fabricated several such devices on a variety of substrates and measured their response between 700 and 120nm with special emphasis around the band edge near 220nm. Steady state and transient response have been measured as a function of bias conditions. Transient response in this case refers to initial overshoot, undershoot, and increased dark current in response to a chopped vacuum ultraviolet (VUV) light signal for times on the order of seconds. We compare steady state quantum efficiency results to a simple model, discuss the characteristics of response versus applied voltage, and examine relationships between response and substrate properties.
INTRODUCTION The present work was motivated by a need to assess the quality of various synthetic diamond materials for use as radiation detectors. The potential of diamond for radiation detection has long been recognized[1][2][3]. Recent work with diamond metal-semiconductor-metal (MSM) devices for recording high-intensity, short pulses of high energy radiation has demonstrated the utility of diamond in this detection regime[4]. Our work has been directed toward a complementary detection application for vacuum ultraviolet (VUV) imaging in astrophysical observing missions, principally for imaging the sun. Here, the fluxes are low, of order 103photons/cm 2 /sec, and the objects of interest are relatively static, evolving over periods of minutes or hours. These conditions require detectors that integrate detected flux before being read out. This added complexity requires more control over diamond properties than can be achieved with natural diamond. While the basic MIS capactior has recently been demonstrated to store charge on natural type-IIb diamond [5], it is likely that two dimensional imagers will need to be fabricated in synthetic diamond. Synthetic diamond is currently produced by a variety of techniques including hot filament CVD, microwave CVD, various acetylene torch techniques, and high-pressure high-temperature (HPHT) ( see [6] for example). None of these techniques has been perfected and each can give diamond with differing defect characteristics. Both single crystal and polycrystalline diamond are concievably useful for detector fabrication given that polycrystalline diamond has been used to make other devices [7][8] and that polycrystalline silicon has been used to make complex optoelectronic devices[9]. The need to quickly evaluate diamond substrates for detector fabrication is clear. The results presented here are intended to
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