Influence of nitrogen doping on photoconductivity properties of a:DLC films

We present photoconductivity, photosensitivity and decay time of photocurrent measured as a function of temperature for both nitrogen-doped and undoped a:DLC films. The a:DLC films were deposited using radio-frequency (RF) glow discharge of methane gas (CH4) as a source of carbon. Several films were doped employing nitrogen (N-2) as the doping gas. The doped and undoped a:DLC films have shown photoconductivity effects in a wide range of temperatures. All photoconductivity parameters, i.e. spectral response, photosensitivity, decay time and photocurrent, were measured for both undoped and doped films. The maximum spectral photosensitivity of doped films shifts to a higher energy, similar to the optical energy-gap measurements. The photocurrent of the doped film is larger by two orders of magnitude than that of undoped film, while the photosensitivity shows an opposite effect. The mobility of doped films (2.43 x 10(-5)) is larger by two orders of magnitude than that of undoped films (5.64 x 10(-7)) at room temperature. In order to provide nanoscale information about the morphological properties of the undoped a:DLC films surface, we have used atomic force microscopoy (AFM). It was found that the roughness of our films increased with increasing thickness of the films, from 0.3 to 1.5 mu m. (C) 1997 Elsevier Science S.A.