PARALLEL AND PERPENDICULAR PHONON-DRAG THERMOPOWER IN SEMICONDUCTOR SUPERLATTICES

Phonon-drag thermopower is calculated in a semiconductor superlattice with temperature gradient parallel and perpendicular to the superlattice axis. Umklapp processes associated with the superlattice periodicity are considered. Numerical results are presented for parameters characteristic of a GaAs/GaAlAs superlattice. Effect of inclusion of umklapp processes is to suppress the magnitude of thermopower parallel to the superlattice axis and to change its sign for Fermi energies near the top of the miniband. The behaviour of thermopower in the plane of the layer is found to be similar to that of a two-dimensional electron gas.