Theory of unconfined excitons trapped by a quantum well.

The energy levels and optical properties of unconfined excitons (excitons made of electron-hole pairs in the barrier material) interacting with a quantum well are studied via a variational method within the effective-mass approximation. The interplay of the relative motion and center-of-mass motion is examined carefully. The coupling of the unconfined excitons with the confined exciton via the emission of an acoustic phonon is examined. The effect of such coupling can produce much enhanced signals in the photoluminescence excitation (PLE) measurements. spectra. We perform simulation of the absorption and PLE spectra of an ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}/\mathrm{GaAs}$ quantum well based on this mechanism and compare our results with the experiment performed by Reynolds et al. [Phys. Rev. B 43, 1871 (1991)].