OPTICAL-PHONON TUNNELING AND THE ELECTRON-SCATTERING RATE

Tunnelling of optical phonons across a quantum well is possible for a polar mode provided its frequency coincides with that of the two inter face modes associated with the barrier. Because of this effect LO mode s could scatter electrons in the well. In this paper we report a calcu lation of the total scattering rate caused by modes in the LO branch o f the barrier material as a function of well width. We show that the f orm of the well-width dependence and the magnitude of the scattering r ate is, to an excellent approximation, the same as that predicted by t he dielectric continuum (DC) model, in which the scattering is caused by barrier interface modes obeying only electrical boundary conditions . This result provides, for the first time, justification for using Fu chs-Kliewer-like interface modes, even though these do not satisfy the necessary mechanical boundary conditions at the interfaces. It comple tes a study of the applicability of the DC model to the calculation of the scattering rates in a quantum well, a study that has already show n it to give a good agreement with the results of the hybrid model as regards the effects of modes in the well are concerned [2]. Our conclu sion is that provided that the frequency-dependence of the coupling st rength of the interface modes is correctly described, differences in d etail concerning the effect of individual modes in the two models are unimportant for the total sum. (C) 1998 Academic Press Limited.