Time-resolved ultrafast carrier dynamics in as-grown nanocrystalline silicon films: The effect of film thickness and grain boundaries

Abstract

In this letter, we have studied transient photoinduced absorption in as-grown nanocrystallinc silicon films with thickness varied from 5 to 30 nm. Effects of quantum confinement (QC) in z-direction and grain boundary distortions alter the carrier dynamics of these films considerably. Based on the determination of critical points in the first Brillouin zone of the band structure of materials, we have time-resolved the relaxation times of surface-related states and indirect valleys. When decreasing the film thickness down to the QC limit (∼ 10 nm) new ultrafast relaxation mechanisms start to play a dominant role in carrier dynamics due to the topological disordering of these ultrathin films. These relaxation mechanisms seem to be related with the traping/ de-traping of the excited carriers prior to recombination. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.