Electronic structure of semiconductor quantum dots

Abstract

The single particle electronic level structure of semiconductor quantum dots (QDs) with a zinc-blende structure, and with size smaller than the bulk exciton Bohr radius, is discussed. Using an empirical tight-binding theory, the energy levels and wave functions of GaAs crystallites containing upto ≈4000 atoms are obtained. The tight-binding (TB) results for the size-dependence of the near-band-edge energy levels and the exciton energy are compared with those obtained using the multiband effective mass approximation (EMA). We find that a simple EMA picture is not even qualitatively correct for the conduction band levels in GaAs QDs, in the size range considered, and particularly in smaller QDs. This is in contrast to CdS and CdSe QDs, for which earlier TB calculations by our group showed that the EMA gives the correct qualitative picture, so that a correspondence between the TB energy levels and those calculated within a spherical multiband EMA could be set up. The reasons for the differences in these materials are discussed.