Photoconductive and photovoltaic properties of CVD diamond films

Free-standing undoped polished MPCVD diamond films (200-300 μm 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 -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 5×105 (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.