The Optical Band Gap of Silicon Quantum Dots: The Influence of Surface Passivation

Abstract

To investigate the mechanism of the photoluminescence from silicon nanostructures, we perform computer simulation using tightbinding scheme and empirical pseudo-potential Hamiltonian. The optical and electron correlation effects on confinement and the influence of surface states on gap energy is studied for silicon quantum dots. We examined the variation of the band gap as a function of sizes of small silicon quantum dots with hydrogen and oxygen passivation at the surface (SinHm, and SinOm). It is observed that the gap decreases with increasing dot size in pure clusters. Furthermore, the band gap increases on passivating the surface of the dot with hydrogen and oxygen respectively. Both quantum confinement and surface passivation determine the optical and electronic properties of silicon nanoclusters. Further, the oxygen passivated surface possess a wider energy gap than the hydrogenated surface. The room temperature visible luminescence is due to radiative recombination of electrons and holes in quantum confined nanostructures in which the localized surface states play a pivotal role. The entire energy spectrum starting from the very low lying ground states to the very high lying excited states for silicon dots having 3 to 44 atoms per dot are computed. The role of surface states on the gap energy, HOMO-LUMO states as well as the effect of passivation on the confinement has also been examined. The results are compared and in conformity with other model calculations and experimental observations.