Effect of valence-band hybridization on the exciton spectra in GaAs-Ga_1−xAl_xAs quantum wells

An investigation is made into the effect of valence-band coupling on Wannier excitons in GaAs-Ga_1−xAl_xAs quantum wells with well widths ranging from 30 to 200 Å. The results of our calculation show that the effect is twofold. On the one hand, hole-subband nonparabolicity due to mixing of the heavy- (HH) and light-hole (LH) states causes an increase in the binding energies E^ex, of both ground- and excited-state excitons; on the other hand, the different orbital behaviors of the spinor components of the excitonic wave function result in a decreased E^ex of s-state excitons and an increased E^ex of p- and d-state excitons. The former effect dominates in narrower wells and the latter effect dominates in wider wells. The two-band model is a good approximation for calculating E^ex(HH1), but can cause a significant error in calculating E^ex(LH1) in wider wells because of the stronger coupling between exciton states from different subbands.