Hydrogen-related gap states in the near surface of chemical vapor deposited homoepitaxial diamond films

We have investigated electrical and optical properties of high-conductivity layers existing in the near surface of as-deposited (hydrogenated) homoepitaxial diamond films. It is found from Hall effect measurements that both hydrogenated undoped and B-doped diamond films have a high concentration of holes (similar to 10(12) cm(-2) ar 297 K), while the conventional oxidized B-doped films have a much lower concentration of holes (similar to 10(8) cm(-2) at 297 K) which corresponds to that of doped B-atoms. The temperature dependence of the forward I-V characteristics of the Al-Schottky barrier to the high-conductivity layers indicates the existence of high-density gap states which act as accepters in the layer. As for the cathodoluminescence study, a broad luminescence peak at around 540 nm is observed in the near surface of hydrogenated films, but not in oxidized films. These experimental results suggest that hydrogen-related gap states due to the hydrogen incorporation exist in the near surface of the hydrogenated diamond films, some of which act as shallower accepters causing the high conductivity. (C) 1997 Elsevier Science S.A.