On the scattering of electrons by polar optical phonons in quasi-2D quantum wells

Abstract

Numerical calculations have been made of the rates of scattering and momentum relaxation of electrons caused by unscreened polar optical phonons in quasi-two-dimensional layers, using a simple infinite-depth square-well model. The results are compared with approximate analytic formulae, and with the situation in the bulk. Some of the major differences from scattering in the bulk are (i) an abrupt threshold for phonon emission appears, (ii) rates just above threshold are enhanced and (iii) the scattering just above the threshold of emission is more isotropic. These differences are intimately related to the energy dependence of the density of states and to the polar interaction, and are expected to be largely independent of the model. The form of the polar interaction strongly favours intra-sub-band scattering over inter-sub-band scattering and this effect has consequences for the luminescent spectrum expected from hot injected carriers. The large increase of the momentum relaxation rate at the emission threshold has consequences for transport phenomena.