ELECTRONIC-STRUCTURE OF SEMICONDUCTOR QUANTUM DOTS

The single particle electronic level structure of semiconductor quantu m dots (QDs) with a zinc-blende structure, and with size smaller than the bulk exciton Bohr radius, is discussed. Using an empirical tight-b inding theory, the energy levels and wave functions of GaAs crystallit es containing upto approximate to 4000 atoms are obtained. The tight-b inding (TB) results for the size-dependence of the near-band-edge ener gy levels and the exciton energy are compared with those obtained usin g the multiband effective mass approximation (EMA). We find that a sim ple EMA picture is not even qualitatively correct for the conduction b and 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 ea rlier TB calculations by our group showed that the EMA gives the corre ct 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 discus sed.