PHOTODETECTORS WITH CVD DIAMOND FILMS - ELECTRICAL AND PHOTOELECTRICAL PROPERTIES PHOTOCONDUCTIVE AND PHOTODIODE STRUCTURES

Free-standing and silicon-supported diamond films have been used to fa bricate photoconductive and photodiode structures for UV light detecti on. Planar and sandwiched photoconductive structures have been made on microwave plasma-grown free-standing CVD polycrystalline diamond film s of 200 mu m and 15 mu m thicknesses, respectively. A photodiode sand wich structure was obtained on thin (similar to 2 mu m) boron-doped di amond films grown on silicon substrate by hot filament CVD. Parameters of defects in the structures were studied by charge-based deep-level transient spectroscopy (Q-DLTS). Planar photoconductive detectors afte r annealing in air showed a low dark current <10 pA and a high spectra l discrimination-a 10(4) higher response to 200 nm than to visible (60 0 nm) wavelengths. The dark current was <10 pA. The turn-off time of t he device following exposure to light was less then 10 ms. It was foun d that the annealing in air decreases density of point defects more th an order and strongly increases wavelength discrimination. The sandwic h photodiodes showed a sharp cut-off in photoresponse at 220 nm with a quantum yield of about 0.3 and a photovoltage in the open circuit reg ime of up to 1.6 V. Such photodiodes can be used not only for light de tection but also for light energy transformation into electrical energ y as in a photovoltaic cell. (C) 1998 Elsevier Science S.A.