Comparative Study of Charge Transport in Si and Ge Nanowires

We report on detailed calculations of charge mobility in small diameter Ge nanowires, and a comparison with equivalent diameter Si nanowires. The basis for the calculations is provided by band structure calculations within a sp(3)d(5)s* tight-binding scheme. Charge-phonon scattering rates are evaluated using Fermi's Golden Rule. Mobility calculations are performed using multi-subband momentum relaxation time approximation. In addition, high-field charge transport is also compared among the two classes of materials. High-field transport results are evaluated using ensemble Monte Carlo simulation. High-field transport behavior is found to be qualitatively similar between Si and Ge nanowires, while low-field mobility results show interesting behavior when compared to bulk Si and Ge. Besides providing. a comparative analysis of the behavior of these materials, our work also helps to place an upper bound on their expected electronic response.