ELECTRICAL-CONDUCTION MECHANISMS IN POLYCRYSTALLINE CHEMICALLY VAPOR-DEPOSITED DIAMOND FILMS

The electrical conduction in polycrystalline chemically vapour-deposited diamond films has been studied. The d.c. current-voltage characteristic consists of an ohmic region at low voltages and a highly non-linear region at high voltages. As-grown films are dominated by ohmic conduction with a small activation energy through disordered graphitic regions between grains and at the surface of the films. When the as-grown' film is annealed at 670 K, the conductivity of the ohmic region is drastically decreased by several orders of magnitude and becomes governed by traps with the activation energy of 0.93 eV. Moreover, the existence of the hopping conduction is demonstrated by frequency-dependent conductance measurement. Hydrogenation of the annealed film leads to an increase in the conductivity at around room temperature with little change in the high temperature conductivity governed by 0.93 eV level. Poole-Frenkel conduction is observed in the non-linear region at high voltages for all films regardless of treatment processes.