Investigation of the effect of hydrogen on electrical and optical properties in chemical vapor deposited on homoepitaxial diamond films

We have investigated electrical and optical properties of the high-conductivity layers formed in both undoped and B-doped diamond films prepared by chemical vapor deposition, It is found that both hydrogenated undoped and B-doped diamond films have high-concentration holes of similar to 10(18) cm(-3) at 297 K. These films exhibit little temperature dependence of the hole concentration between 120 and 400 K, while that of the oxidized B-doped film has a strong temperature dependence with an activation energy 0.38 eV. The Hall mobility of all the hydrogenated films of similar to 30 cm(2)/Vs at 297 K is one to two orders of magnitude smaller than that of the oxidized B-doped film and increases with increasing temperature. The I-V characteristics of Al-Schottky contacts to the hydrogenated undoped film show excellent rectification properties and the temperature dependence of their forward characteristics is well explained by a junction theory inclusive of the tunneling process, i.e. thermionic-field emission theory, indicating that the depletion layer becomes thin due to high-density space charge in the depletion layer. We have also found a broad cathodoluminescence peak at around 540 nm in the hydrogenated films which disappears with subsequent oxidation treatment, indicating the existence of hydrogen-related gap states in the subsurface region of as-deposited homoepitaxial diamond films. High density hydrogen is detected in the subsurface region of the hydrogenated films by secondary ion mass spectrosccopy. These experimental results suggest the existence of hydrogen-induced shallow accepters in the surface region of as-deposited (hydrogenated) diamond films and that the difference between the hydrogenated and the oxidized films observed in both electrical and optical properties originates from hydrogen incorporated in the subsurface region. (C) 1997 American Institute of Physics.