Hydrogen-Induced Luminescent States In The Subsurface Region Of Homoepitaxial Diamond Films

We found the existence of hydrogen-induced luminescent states in the subsurface region of chemical-vapor-deposited homoepitaxial diamond films by means of cathodoluminescence (CL). A specific broad peak at around 540 nm is observed in both as-deposited diamond films and those treated by hydrogen plasma at 800 °C, but not in conventional oxidized films. The accelerating voltage dependence of the CL spectra indicates that the luminescent states related to the 540 nm peak exist in the surface region and decrease abruptly with increasing the depth from the surface, showing that the depth distribution of the states slightly depends on the hydrogenation duration. Although the 540 nm peak is not observed in the films hydrogenated at 500 °C, it appears once the films are irradiated by an incident electron beam. It indicates the existence of a metastable configuration of hydrogen or its complex forms in the diamond films hydrogenated at low temperatures and a relaxation occurs into a stable one which produces luminescent states by the electron-beam irradiation.