Formation and characteristics of undoped and doped tetrahedral amorphous carbon films

Synthesis of undoped and doped tetrahedral amorphous carbon (ta-C) films has been achieved using magnetic field filtered plasma stream system in an ambient gas of pure Ar and Ar with N-2, respectively. The optical and electrical properties of these films as a function of the substrate bias voltages (V-b) or nitrogen partial pressures (P-N) have been studied using UV-visible optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and measurements of electrical conductivity. The results show that ta-C films with a high sp(3) fraction were formed when the V-b was in the range of -10 to -50 V. The optical band gap of such ta-C films was found to be larger than 3 eV. The incorporation of nitrogen into the ta-C films deposited at low P-N (P-N<25%), results in a slight drop in activation energy, which indicates that there is evidently some doping effect of nitrogen. The configurations of N atoms in ta-C network are identified and discussed. (C) 1999 Published by Elsevier Science S.A. All rights reserved.