Bulk Negative Differential Conductivity in Germanium: Theory

Two mechanisms have been proposed for the bulk negative differential conductivity of n-type germanium first observed by Elliott et al. These are discussed with reference to recent Monte Carlo calculations in which effects due to intravalley acoustic phonon scattering, 〈100〉 and 〈000〉 minima and ellipsoidal constant energy surfaces are explored. Strong evidence is presented that electron transfer to 〈100〉 minima causes this negative conductance. The origin of its temperature and orientation dependence is discussed.