Coherent intraband and interband dynamics in double quantum wells: Exciton and free-carrier effects

Exciton energies and eigenfunctions in asymmetric double quantum wells are calculated as functions of an applied electric field. From these data, absorption spectra are calculated and the localization behavior of the excitonic states is investigated. The coherent dynamics in asymmetric double quantum wells, which is strongly influenced by excitonic effects, is analyzed by a numerical solution of the multisubband semiconductor Bloch equations. Under resonance conditions the oscillating dipole moment leads to a coherent terahertz emission. In general, the spectrum of this radiation has contributions due to both, the free-carrier and exciton energies, the details being determined by the excitation and dephasing conditions. The calculated absorption spectra and the frequency of the terahertz radiation are in good agreement with recent experiments.