Comparative measurements of acceptor concentration at the growth and nucleation side of microwave plasma CVD polycrystalline diamond films

Abstract

Comparative studies of the electrical and optical properties of the growth and nucleation surfaces of free-standing boron-doped polycrystalline diamond films were performed. The diamond films, approximately 0.4 mm thick, were grown in a microwave plasma chemical vapor deposition (MPCVD) reactor. Capacitance–voltage measurements at electrolytic and solid-state contacts, charge-based deep-level transient spectroscopy and IR absorption measurements were used to determine the parameters of the electrically and optically active intrinsic and boron-induced defects in the diamond films. The total boron concentration was obtained by a SIMS method. In the diamond bulk adjacent to the nucleation side, consisting of submicron-sized grains, the concentrations of both the intrinsic and boron-induced acceptor defects were found to be approximately one order of magnitude higher than those near the growth surface, which is coarse-grained. This difference is tentatively attributed to the elevated concentration of crystal lattice defects near the nucleation surface, which, in addition to boron atoms, play the role of acceptors in diamond. Our experimental data (electrical and optical) show that these additional acceptors are mainly localized near the nucleation side of the thick boron-doped MPCVD diamond films.