Nanovoid-related large redshift of photoluminescence peak energy in hydrogenated amorphous silicon

A large redshift of the photoluminescence (PL) peak energy is found in hydrogenated amorphous silicon films prepared by hot-wire chemical-vapor deposition with a high-growth rate greater than or equal to 50 Angstrom /s. The PL intensity is as high as that in the standard film and its temperature dependence shows thermalization behavior. The origin of the redshift is clarified by employing H-1 nuclear magnetic resonance and mass density measurements. A similar to2% volume fraction of tube-like nanoscale voids is identified. The long spin-lattice relaxation time of H-2 in the nanovoids implies a negligible density of silicon dangling bonds on the nanovoid surfaces. We suggest that highly strained bonds on these surfaces form broad conduction-band tail states that are responsible for the PL redshift. (C) 2002 American Institute of Physics.