Charge transport in boron-doped diamond thin films

Detailed studies are reported for the temperature dependence of nominally undoped and boron-doped diamond thin films over the temperature range 400 to 150K; boron doping concentrations in the films range from 20 to 968 parts per million. In all samples, no single-valued activation energy is observed although the dependence on temperature systematically decreases with increasing boron con-centration. This suggests that the acceptor states introduced by the boron are themselves energetically situated in a relatively high density of impurity or defect states extending from the valence band edge. It is believed that charge transport in these films involves a combination of extended-state conduction and hopping within these distributions of localized states and evidence of impurity band formation is observed.