Anomalous splitting of the hole states in silicon quantum dots with shallow acceptors

Abstract

Hole wavefunctions and energy spectra have been calculated in a silicon quantum dot witha shallow acceptor. Within the framework of the envelope function approach we have foundanomalously strong splitting of the energy levels caused by the Coulomb and the spin–orbitinteractions as compared to bulk silicon. If the quantum dot has been doped with boron,the short range part of the Coulomb field turns out to be weak, and the long rangehydrogenic part plays a crucial role in the energy splitting. In the case where the dot isdoped with any other element of the third group, the role of the short range Coulombinteraction becomes determinative. The latter provides stronger energy splitting comparedto that in the model of hydrogen-like impurity. In both cases the energy of the splittingsubstantially exceeds the typical bulk values for these acceptors due to the quantumconfinement effect. We have also analysed the charge distribution in the dot andthe hole spectrum, depending on the acceptor position inside the nanocrystal.