THEORY OF UNCONFINED EXCITONS TRAPPED BY A QUANTUM-WELL

The energy levels and optical properties of unconfined excitons (excit ons made of electron-hole pairs in the barrier material) interacting w ith a quantum well are studied via a variational method within the eff ective-mass approximation. The interplay of the relative motion and ce nter-of-mass motion is examined carefully. The coupling of the unconfi ned excitons with the confined exciton via the emission of an acoustic phonon is examined. The effect of such coupling can produce much enha nced signals in the photoluminescence excitation (PLE) measurements. s pectra. We perform simulation of the absorption and PLE spectra of an InxGa1-xAs/GaAs quantum well based on this mechanism and compare our r esults with the experiment performed by Reynolds et al. [Phys. Rev. B 43, 1871 (1991)].