Analysis of Phonon-Drag Thermomagnetic Effects in n-Type Germanium*

Abstract

A study has been made of the Nernst effect and the variation of thermoelectric power with magnetic field for single-crystal samples of n-type germanium of various orientations and impurity concentrations, at fields up to 18,000 gauss and temperatures from 275° to 60°K and below. Except at the highest temperatures, both effects arise predominantly from that part of the thermoelectric power which is due to phonon drag. All observations can be quantitatively accounted for by theory. They yield information about the dependence of the relaxation times for phonon-phonon scattering on the frequency of the phonons, and establish with some certainty the conclusion that four-phonon collisions are much less important than three-phonon collisions in the pertinent range of temperatures and phonon frequencies. A uxiliary investigations have shown that the quantization of electron orbits in a magnetic field has only a small effect on transport properties when the cyclotron level spacing is less than thermal energy. The mean free path of electrons is shown to be energy-independent, as acoustic-scattering theory predicts. The absolute mobility can be predicted to within 10 per cent or better from data on the fractional changes of resistance with stress and magnetic field. A more detailed summary of the conclusions and implications of the present work is given in Section IX.