Shape dependence of the band gaps in luminescent silicon quantum dots

Abstract

Silicon nanoparticles exhibit quantum confinement and function as optoelectronic devices whose optical properties are known to depend strongly on size and surface termination. The effect of nanoparticle shape on optical properties, however, has not yet been investigated. In this work we use tight binding and density functional theory simulations to study the HOMO–LUMO gaps of hydrogen-terminated silicon nanoparticles as a function of shape and size. It is shown that optical properties are strongly dependent upon nanoparticle shape, and in particular that octahedral nanoparticles exhibit significantly (up to 0.2 eV) larger band gaps than cubic or pseudo-spherical nanoparticles of the same volume. Control of the shape of nanoparticles via the tuning of the thermodynamic conditions in which they are formed may allow the formation of silicon nanoparticles with emission wavelengths running across the full visible range.