Optical and electronic properties of hydrogenated silicon nanoclusters and nitrogen passivated silicon nanoclusters: a density functional theory study.

Silicon nanoclusters have become significant research interest due to their potential application to optoelectronic devices in visible range. We investigate the electronic and optical properties of hydrogenated and nitrogen-passivated silicon nanoclusters using density functional theory calculations. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of nanoclusters have varying sizes. They are systematically studied using the conventional local density approximation, the generalized gradient approximation, and the time-dependent density functional theory calculations with hybrid functional. The HOMO-LUMO gap is found to decrease monotonically as the size of nanocluster increases. Introducing one and two nitrogen passivants to a Si29H36 nanocluster, we find that the HOMO-LUMO gap decreases as the number of nitrogen passivants increases. It suggests that multi-nitrogen passivants may enable light emission in visible range from smaller clusters.