HIGH-FIELD CONDUCTIVITY OF POLYCRYSTALLINE DIAMOND FILMS

Results of conductivity measurements on polycrystalline diamond films at field strengths up to 10(6) V/cm-1 are presented. Nominally undoped or nitrogen-containing CVD diamond films were prepared in a microwave plasma reactor using different gas mixtures and substrate pretreatments. Film compositions were characterized by secondary-ion mass spectrometry, and film qualities by Raman spectroscopy. Sample thicknesses were determined using capacitance measurements. High-field conductivity was determined from current-voltage characteristics for randomly oriented films prepared with oxygen- and nitrogen-containing source gas. An increase in resistivity was found in both cases. The results are discussed in terms of the reduction of the graphitic phase content and compensation effects respectively. Heteroepitaxially grown films were also preliminarily characterized and the results are compared with those obtained from randomly oriented samples.