Photoinduced defects in wide-gap materials: Hydrogenated amorphous silicon-carbon and silicon-nitrogen films

Abstract

Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps in the range 1.9–4.0eV have been deposited by the 13.56 MHz plasma-enhanced chemical vapour deposition technique from SiH₄ + C₂H₂ (+H₂), SiH₄ + NH₃ (+H₂), gas mixtures. The deposition conditions have been chosen so as to obtain device-quality films already successfully applied in optoelectronic technology. The films have been light soaked in the average weather conditions solar spectrum (air mass 2.0) for times up to 90 h, monitoring the absorbed energy. The optical properties have been measured after each occurrence of damage, and the defect density evolution due to light soaking was determined by photothermal deflection spectroscopy. An increase in the density of defects with light exposure was observed in all samples strongly dependent on carbon or nitrogen gas sources, plasma conditions and initial properties.