HIGH-FREQUENCY PHOTOCONDUCTIVITY OF CVD DIAMOND FILMS

Photoconductivity measurements on undoped diamond material can be stro ngly affected by the nature of the electrical contacts, due to the wid e band gap and high resistivity. We have used a contactless technique based on high frequency electrical measurements in order to probe the photoconductivity sigma(HF-photo) of CVD diamond films grown by a micr owave assisted technique. Resonant methods, at 9.192 GHz are carried o ut in a microwave cavity by a reflection spectrometer. Samples are irr adiated by modulated UV light. The photoconductivity sigma(HF-photo) i s deduced from the variation of the quality factor and from the freque ncy shift. The samples studied were deposited under various growth con ditions (temperature, gas mixture, etc.). The measured high frequency photoconductivity values were compared with the physical and electrica l properties measured from conventional techniques (Raman spectroscopy , current-voltage and charged particle induced conductivity characteri sation). The potential of this contactless high frequency measurement technique for CVD diamond characterisation is discussed. (C) 1998 Else vier Science S.A.