Surface quenching of optically generated carriers in thin-film hydrogenated amorphous silicon: Picosecond transient-grating experiments

Abstract

Subnanosecond-timescale transient-grating experiments are used to investigate the dynamics of optically generated charge carriers in thin-film hydrogenated amorphous silicon (a-Si:H) at room temperature. By examining the time dependence of the transient-grating signal as a function of fringe spacing for small fringe spacing, the diffusion constant in the plane of the film ($D_{?}$) is determined. At large fringe spacing, the grating decay becomes independent of fringe spacing and is highly nonexponential. The functional form and rate of the large-fringe-spacing decay change with sample thickness. A model for the effect of surface quenching on the transient-grating decay is presented. The calculations are in good agreement with the data and yield a diffusion constant ($D_{\perp }$) for motion perpendicular to the thin-film plane. $D_{\perp }$=0.4×${10}^{\mathrm{-}2}$ ${\mathrm{cm}}^2$/sec, while $D_{?}$=1.0×${10}^{\mathrm{-}2}$ ${\mathrm{cm}}^2$/sec.