Many-body levels of optically excited and multiply charged InAs nanocrystals modeled by semiempirical tight binding

Abstract

Many-body levels of optically excited and multiply charged InAs nanocrystals are studied with the semiempirical tight-binding model. Single-particle levels of unstrained spherical InAs nanocrystals are described by the sp 3 d 5 s* nearest-neighbor tight-binding model including spin-orbit coupling. For optically excited InAs nanocrystals, first-order corrections of electron-hole Coulomb and exchange interaction to exciton levels and the oscillator strengths of the exciton levels determine several low-lying, bright-exciton levels. The origin of the large oscillator strengths of the bright exciton levels is explained by the analysis of dominant angular momenta of exciton envelope functions. Good agreement with photoluminescence excitation experiments is achieved for the size dependence of the three lowest bright-exciton energies of InAs nanocrystals with radius larger than 20 A. For multiply charged InAs nanocrystals, polarization of the nanocrystal environment is approximated by modeling the environment with a uniform dielectric medium. This polarization model incorporated into the tight-binding model provides a reasonable description of electron and hole addition energies in scanning tunneling spectroscopy experiments.