BREAKDOWN OF THERMIONIC EMISSION THEORY FOR QUANTUM-WELLS

Carriers escape from quantum wells into barriers via carrier-polar opt ical phonon absorption is theoretically studied in multisubband quantu m well structures. We find that carriers in each subband have their ow n minimum escape time when the energy difference between the band edge s of the subband and the barrier matches the energy of a longitudinal optical phonon. Compared to the calculations from classical thermionic emission theory, we find that the thermionic emission theory is no lo nger valid when the width or the depth of quantum wells is small.