Electronic and optical fine structure of GaAs nanocrystals: The role of d orbitals in a tight-binding approach

摘要

Electronic structure and optical spectra of GaAs nanocrystals for a wide range of sizes are studied by using both sp~3s~* and sp~3s~*d~5 nearest-neighbor tight-binding models. Our results show that the inclusion of d orbitals into a minimal basis set is necessary for a proper description of the lowest electron states, especially in the strong confinement regime. For dot sizes below 2.5 nm, the ground electron state is primarily built of L-point bulk band states, giving the nanocrystals indirect-gap character. Simpler sp~3s~* models yield an incorrect description of electron states made from bulk band states away from the Brillouin zone center. In contrast, sp~3s~*d~5 models are able to provide a consistent picture of the main optical features in agreement with experiments.