ESCAPE FROM QUANTUM-WELLS VIA POLAR OPTICAL PHONON-SCATTERING

We calculate the rate for electrons confined in a quantum well to escape to unbound, current-carrying states by polar optical phonon scattering. We explicitly include the two-dimensional to three-dimensional nature of the transition and choose final state wave functions which are genuinely unbound. We find that the escape rate decreases dramatically as the well depth increases, even for electrons with more than enough energy to surmount the well walls. The real-space transfer rate is much smaller than either the bulk scattering rate or the confined bound-to-bound scattering rate. We explore this phenomenon and give a detailed explanation of the rate depression. We also show that the electron escape rates have a strong directional dependence in asymmetric wells. Electrons scatter out preferentially in the direction of the more abrupt interface.