ELECTRONIC TRANSPORT AND DENSITY OF STATES DISTRIBUTION IN DIAMOND THIN-FILMS

The results of measurements which shed light on the important question of the density and distribution of localized states within the bandgap of hot-filament grown diamond thin films are discussed. These include temperature dependence studies of undoped and boron-doped diamond film, over the temperature range 400-150 K, with a range of doping concentrations. In all samples, no single-valued activation energy is observed although the dependence on temperature systematically decreases with increasing boron concentration. This suggests that states due to boron overlie a relatively high density, N(E), of localized acceptor states already present in nominally undoped diamond thin films. Using space-charge limited hole currents, N(E), 0.8 eV above the valence band, is ∼ 1015 cm-3eV-1 but rises rapidly, within 0.2 eV, to ∼ 1018 cm-3eV-1. These states have also been detected by the observation of electrical compensation in nitrogen-doped films. Charge transport in these diamond films range from extended state to impurity hopping and band conduction. The implications of these results for field-effect phenomena and diamond thin film transistors are discussed. © 1992.