An impedance spectroscopic study of n-type phosphorus-doped diamond

An important development in the field of diamond electronics has been the production of n-type electrical characteristics following homoepitaxial diamond growth on (111) diamond in the presence of phosphorus-containing gases. Several studies have reported that a phosphorus donor level forms with an activation energy in the range of 0.43–0.6eV; the ground state for the donor level is considered to be at 0.6eV. Little is currently known about other electrically active defects that may be produced alongside the donor state when phosphorus is introduced. In this paper we report upon the use of impedance spectroscopy, which can isolate the differing components that contribute to the overall conductivity of the film. In Cole-Cole plots, two semicircular responses are observed for all temperatures above 75°C; a single semicircle being seen at temperatures below this. The results suggest the presence of two conduction paths with activation energies of 0.53 and 0.197eV. The former can be attributed to the phosphorus donor level, being lower than 0.6eV due to reduced mobility within the film at elevated temperatures. The latter is discussed in terms of defects in the P+-doped region under the Ohmic contacts being used.