  Electron transport in Ge at various temperatures down to 20 mK has been
investigated using particle Monte Carlo simulation taking into account ionized
impurity and inelastic phonon scattering. The simulations account for the
essential features of electron transport at cryogenic temperature: Ohmic
regime, anisotropy of the drift velocity relative to the direction of the
electric field, as well as a negative differential mobility phenomenon along
the <111> field orientation. Experimental data for the electron velocities are
reproduced with a satisfactory accuracy. Examples of electron position in the
real space during the simulations are given and evidence separated clouds of
electrons propagating along different directions depending on the valley they
belong.
