Effects of nitrogen doping on the electrical conductivity and optical absorption of ultrananocrystalline diamond/hydrogenated amorphous carbon films prepared by coaxial arc plasma deposition

摘要

3 at.% nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C: H) films were synthesized by coaxial arc plasma deposition. Optically, the films possess large absorption coefficients of more than 10(5) cm(-1) at photon energies from 3 to 5 eV. The optical band gap was estimated to be 1.28 eV. This value is smaller than that of undoped films, which might be attributable to increased sp(2) fractions. The temperature dependence of the electrical conductivity implies that carrier transport follows a hopping conduction model. Heterojunctions with p-type Si substrates exhibited a typical rectifying action. From the capacitance-voltage characteristics that evidently indicated the expansion of a depletion region into the film side, the built-in potential and carrier concentration were estimated to be 0.51 eV and 7.5 x 10(16) cm(-3), respectively. It was experimentally demonstrated that nitrogen-doped UNCD/a-C: H films are applicable as an n-type semiconductor. (C) 2016 The Japan Society of Applied Physics