EXCITON IONIZATION IN A QUANTUM-WELL STUDIED BY SURFACE ACOUSTIC-WAVES

Photogenerated excitons in a semiconductor quantum well are ionized by the strong lateral piezoelectric field of an intense surface acoustic wave. The ionization process is directly observed by the absorption o f a second sound wave probing the areal conductivity of the photogener ated charges. Above a certain threshold field strength of the pumping surface wave the neutral excitons are dissociated into electron-hole p airs, which is indicated by a sudden onset of absorption of the probe wave. By selectively tuning the energy of the exciting laser, the diss ociation of both quasi two-dimensional excitons in the quantum well as well as three-dimensional excitons in the barrier material can be obs erved.