Electric field effects on excitonic quantum beats in a single quantum well embedded in a GaAs/AlAs superlattice

Abstract

We have investigated the characteristics of the quantum beat of excitons confined in a GaAs single quantum well (6.4 nm) embedded in the center of a GaAs (3.2 nm)/AlAs (0.9 nm) superlattice (SL) from the viewpoint of the resonant coupling between the subband states in the single quantum well (SQW) and the Wannier--Stark-localization states in the SL with the use of a reflection-type pump-probe technique. The resonant couplings, which cause anticrossing behaviors of relevant transition energies, were observed by electroreflectance spectroscopy and analyzed by calculating the eigenenergies as a function of electric field strength. It is found that the frequency and intensity of the quantum beat between the heavy-hole and light-hole excitons in the SQW significantly change under the resonant coupling conditions of the electron states. The changes of the quantum-beat properties result from the formation of bonding and antibonding electron states which modifies the excitonic transition properties in the SQW as a function of electric field strength. The experimental results of the quantum beat are reasonably explained by the electric-field-strength dependence of the energies and transition probabilities of the excitons in the SQW observed from electroreflectance spectra.