Photoconductive and photovoltaic properties of CVD diamond films

Free-standing undoped polished MPCVD diamond films (200-300 mu m thick) have been used to fabricate photoconductive and photodiode structures for UV light detection. Multifinger planar Au/Cr electrodes of the photoconductive structures were realized on the diamond surface by lithographic technique. The sandwich semitransparent Ni electrodes of the photodiode structures were deposited by a magnetron sputtering on both sides of the diamond films. The films showed conductivity less then 10(-15) S/cm at room temperatures with activation energy close to 1 eV and low concentration of the electrically active defects according to charge-based deep-level transient spectroscopy (Q-DLTS). The distinct trap levels with activation energy of 0.5, 0.7 and similar to 1.3 eV were evaluated. Planar photoconductive detectors with electrodes on the growth side showed the dark current below 1 pA at 10 V bias voltage with spectral discrimination ratio higher than 5 X 10(5) (at 50 V bias) in the 210-270 nm wavelength range. Two orders of magnitude lower responsivity were found on the nucleation side. The sandwich photodiodes showed a sharp cut-off in photoresponse at 220 nm and photovoltage as high as 2.3 V in open circuit regime. (c) 2004 Elsevier B.V. All rights reserved.