Signatures of trions in the optical spectra of doped semiconductor nanorings in a magnetic field

A density-matrix theory for absorption changes in semiconductors induced by electron or hole occupations is outlined. Bound and unbound trions are included via four-point correlation functions representing electron–hole pair transitions in the presence of carrier populations. The spectra calculated for semiconductor nanorings show bleaching of the exciton resonance and induced absorption at energies corresponding to transitions to bound and unbound trion states. Without a magnetic field, induced absorption below the exciton line due to bound negatively (positively) charged trions appears when the two electrons (holes) of the trion are in different bands. A magnetic field introduces characteristic modifications of the spectra that can be attributed to the Aharonov–Bohm effect. It may lead to the formation of additional bound magneto-trion states.