Coherent terahertz emission from coupled quantum wells with exciton effects

We have developed a theoretical model for investigating the recent observation of terahertz electromagnetic pulse emission from GaAs–Ga0.8Al0.2As asymmetric coupled-quantum-well structures. We use a multisubband model that takes into account Coulomb interactions among all electrons and holes, particularly the exciton effects. The calculations indicate that the terahertz emission originates from the quantum beat between heavy-hole excitons in the narrow well and shifts to two resonantly coupled exciton states in the coupled quantum wells and later to heavy-hole excitons in the wide well as the applied dc field is increased. Furthermore, exciton, interband, and intersubband dephasing times determine the characteristics of the radiation fields. The theoretical results are in good agreement with those of previous experiments.