Quantum Confinement Effect in Pristine and Oxygen Covered Silicon Nanocrystals with Surface States

Abstract

Absorption spectra for pristine silicon and oxygen capped silicon nanocrystals (ncs) are computed using time dependent local density approximation (TDLDA) in the size regime of 1.0 to 1.5 nm. These clusters show very small highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps. This indicates presence of surface states. The partial density of states (PDOS) for these clusters confirms the presence of surface states when compared to the corresponding ncs with hydrogen passivation. The HOMO–LUMO gaps do not show any size dependence. However the optical absorption gaps show the quantum confinement effect (QCE) for both the types of clusters. The oxygen capped silicon ncs are prepared following the wet chemical route. The optical absorption spectrum of experimentally prepared ncs is compared with the computed one. Experimental results support the theoretical argument explaining the QCE in these clusters.