EFFECT OF MECHANICAL-STRESS ON THE ABSORPTION-BAND TAIL IN POLYCRYSTALLINE DIAMOND FILMS

Diamond films were deposited by plasma deposition of acetylene (1-5 vol.%) and hydrogen mixture on different substrates (Si, mica and quartz). The films were polycrystalline in nature, as revealed by transmission electron microscopy studies. Optical properties of the films were studied in the wavelength range 0.18-2 mu m. Both direct and indirect transitions were found to be present in these films. The mechanical stress at the grain boundary region of diamond film seems to contribute significantly towards the optical absorption below the bandgap. The intercrystalline barrier height E(b) and trap state density Q(t) were obtained from the analysis of the grain boundary effects on the optical properties of the material.