Charged excitons in direct-gap semiconductors

Abstract

The charged excitons are moving bound states of an exciton and an electron or a hole in semiconductors. The theory of these charged quasiparticles is given for direct-gap materials in the framework of the effective-mass approximation, taking into account the spin-orbit coupling and the electron-hole exchange interaction as a perturbation. The special cases of CuCl and CuBr are studied more extensively because they correspond to the most important binding energies. As a result charged excitons are stable enough to be observed in CuCl and CuBr. Arguments are given in favor of the interpretation of some lines as due to transitions between positive or negative charged excitons and free holes or electrons.