A large red-shift of the photoluminescence peak energy was found in hydrogenated amorphous Si films prepared by hot-wire chemical-vapor deposition with a growth rate greater than 5nm/s. The photoluminescence intensity was as high as that in the standard film and its temperature dependence showed thermalization behavior. The origin of the red-shift was clarified by employing 1H nuclear magnetic resonance and mass density measurements. An approximately 2% volume fraction of tube-like nanoscale voids was identified. The long spin-lattice relaxation time of H2 in the nano-voids implies a negligible density of Si dangling bonds on the nano-void surfaces. It was suggested that highly strained bonds on these surfaces formed broad conduction-band tail states that were responsible for the photoluminescence red-shift.

Nanovoid-Related Large Redshift of Photoluminescence Peak Energy in Hydrogenated Amorphous Silicon. D.Han, G.Yue, K.Wang, J.Baugh, Y.Wu, Y.Xu, Q.Wang: Applied Physics Letters, 2002, 80[1], 40-2