A tight-binding representation of electron-hole exchange interaction in semiconductors

The electron-hole exchange interaction in semiconductors is analyzed in the framework of the empirical tight-binding method. It is demonstrated that i ntra-atomic and interatomic contributions to the long-range exchange intera ction enter in an inequivalent way. In particular, for the Gamma (6) x Gamm a (7) exciton in a spherical nanocrystal with a cubic lattice, the dipole-d ipole contribution associated only with the intra-atomic (or intrasite) tra nsitions does not lead to singlet-triplet splitting of the exciton level. T he interatomic transitions, for example, an ion-to-cation transitions betwe en the nearest neighbors in binary semiconductor compounds, determine the s o-called monopole-monopole contribution to the exchange splitting of the Ga mma (6) x Gamma (7) exciton, and this contribution does not vanish in a sph erical nanocrystal. (C) 2001 MAIK "Nauka/Interperiodica".