Preparation and characterization of the stable nc-Si/a-Si:H films

Abstract

High-quality nc-Si/a-Si:H diphasic films with improved stability were prepared b y using the plasma-enhanced chemical vapor deposition technology. In comparison with typical amorphous silicon, the diphasic silicon films possess higher photoc onductivity (two orders larger than that of the amorphous silicon film) and fair ly good photosensitivity(the ratio of the photo-to dark-conductivity is about 10 4) and higher stability (the degradation of the photoconductivity is less than 10% after 24h long light soaking with 50 mW/cm2 intensity at room te mperature ). In addition, the diphasic silicon film has a better light spectra response in the longer wavelength range. The improvement in photoelectronic properties may be attributed to: the existence of the disorder within the amorphous matrix, whi ch breaks the momentum selection rule in the optical transition and, consequentl y, results in the large light absorption coefficient and high photosensitivity; the improved medium range order and low gap states density. Excess carriers gene rated in the amorphous matrix tend to recombine in the embedded crystallites, wh ich suppresses nonradiative recombination within the amorphous matrix and reduce s the subsequent defect creation.