Electrical conduction in undoped diamond films prepared by chemical vapor deposition

Electrical conduction along conducting layers between grains in chemical vapor deposited polycrystalline diamond films has been studied. The dc current-voltage characteristic consists of an ohmic region at low voltages and a highly nonlinear region at high voltages. As-grown films are dominated by the ohmic conduction with a small activation energy through disordered graphitic (disordered sp2 bonded carbon) regions between grains. When the as-grown film is annealed at 670 K, the conductivity of the ohmic region becomes governed by levels at 0.93 eV leading to a drastic decrease by several orders of magnitude, and the nonlinear conduction dominates. Hydrogenation of the annealed sample causes an increase in the conductivity around room temperature with little change in the high-temperature conductivity governed by 0.93 eV levels.