The electron-phonon drag and transport phenomena in semiconductors

This paper presents a review of the present-day knowledge of the electron-phonon drag effects and their role in transport phenomena. It describes approaches, based on the Boltzmann kinetic equation, to the study of interacting subsystems of electrons and acoustic and optical phonons in semiconductors characterized by an arbitrary degree of degeneracy of the charge-carrier gas and non-equilibrium of electrons and phonons in the energy-momentum space. Novel drag mechanisms associated with nonuniform quasiparticle heating (thermal drag) and intense interaction between acoustic and optical phonons (two-stage acoustooptical drag) are discussed. A fundamentally new phenomenon of spatial classification of carriers according to their energies, owing to the electron-phonon drag is considered. The approach employed allows the study of strong electron-phonon drag and some entirely new effects in drag-related transport phenomena. These include primarily an essential effect of drag on current transport, involving in particular sign reversal in the magnetoresistance of isotropic semiconductors. Under certain conditions, drag effects may result in anomalous temperature fields of charge carriers. Validity of the Onsager relations is analyzed for the case of electron-phonon drag.