High frequency photoconductivity of CVD diamond films

Photoconductivity measurements on undoped diamond material can be strongly affected by the nature of the electrical contacts, due to the wide band gap and high resistivity. We have used a contactless technique based on high frequency electrical measurements in order to probe the photoconductivity σ_HF-photo of CVD diamond films grown by a microwave assisted technique. Resonant methods, at 9.192 GHz are carried out in a microwave cavity by a reflection spectrometer. Samples are irradiated by modulated UV light. The photoconductivity σ_HF-photo is deduced from the variation of the quality factor and from the frequency shift. The samples studied were deposited under various growth conditions (temperature, gas mixture, etc.). The measured high frequency photoconductivity values were compared with the physical and electrical properties measured from conventional techniques (Raman spectroscopy, current-voltage and charged particle induced conductivity characterisation). The potential of this contactless high frequency measurement technique for CVD diamond characterisation is discussed.