Optical Properties of Hydrogenated Silicon Clusters with Reconstructed Surfaces

We study the effects of surface reconstruction on the absorption spectra and optical gaps of hydrogen-terminated silicon clusters. The spectra and gaps are computed using an ab initio method based on the linear response theory within the time-dependent local-density approximation (TDLDA). Our calculations show that the structural reconstruction of cluster surfaces produces new absorption bands in the lower part of the spectrum and causes a significant reduction of the optical gap. The optical gaps in surface-reconstructed silicon clusters appear to be similar in size to those in clusters with partially oxidated surfaces. Our results suggest that both surface oxidation and surface reconstruction are essential to resolve disagreements between the optical gaps measured in experiments and theoretical predictions based on a quantum confinement model.