An electron-spectroscopic view of CVD diamond surface conductivity

Three diamond (001) samples were made by CVD growth on synthetic diamond substrates in a same batch of growth, for which sheet resistance in atmospheric environment was confirmed. A simple two-point probe method has been applied to the samples to measure sheet resistance in UHV of 0.2-50 MΩ/square. Soft X-ray-induced secondary electron spectroscopy has been used to determine the Fermi level position in UHV of the samples for which in-UHV sheet resistance values were known. The Fermi level as measured turned out to be 1.1±0.2 eV above the valence band top and stayed at the same position within ∼0.1 eV with the sheet resistance change of an order of 2. On the basis of these findings, a plausible model of surface conductivity of CVD diamond is suggested.