N-type Conduction in Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition Using Li3PO4-Blended Graphite Targets

Co-doping of lithium and phosphorus, which produce shallow donor levels in diamond, was examined for ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition. Semiconducting behaviors were electrically observed and the production of n-type conduction by doping was confirmed thermally. The electrical conductivity is on the order of 10−6 S/cm at room temperature, which suggests that the doping efficiency is extremely small. Totally considering the results of near-edge X-ray absorption fine structure and X-ray photoelectron spectra, Li2CO3 is supposed to be formed in the doped films, which might be a reason for the low doping efficiency.