Analysis of High-Field Hole Transport in Germanium and Silicon Nanowires Based on Boltzmann's Transport Equation

In this paper, high-field hole transport in germanium nanowires was studied by using Boltzmann's transport equation in an atomistic framework. The scattering mechanisms taken into account are phonon and surface roughness. The hole drift velocities of [110], [111], and [112]-oriented germanium nanowires showed negative-differential characteristics, while that of the [001] nanowire did not. The behavior of hole drift velocity was analyzed based on the highly nonparabolic and orientation-dependent valence band structure. High-field hole transport properties in silicon nanowires were also calculated, and the differences between germanium and silicon nanowires were discussed, focusing mainly on momentum and energy relaxation times. The [110], [111], and [112] silicon nanowires showed faster hole drift velocity at high field than the germanium nanowires with the same orientation. This was attributed to faster energy relaxation in silicon nanowires, which mitigates the negative differential mobility in silicon nanowires compared to germanium nanowires.