Electron Mobility in Junctionless Ge Nanowire NFETs

The electron mobility in junctionless (JL) Ge nanowire nFETs with the (110) channel direction is calculated and compared with experimental data. The calculation of the electron mobility is based on the Kubo-Greenwood formula. The wave functions are obtained by solving the self-consistent Poisson-Schrödinger equation. Phonon scattering, surface roughness scattering, and Coulomb scattering (CS) by interface charges and channel charges are considered. Carrier screening on Coulomb charges is calculated using Lindhard's screening theory. At low electron densities, the JL channels have lower electron mobility than inversion-mode (IM) channels due to CS from channel charges. At high electron densities, CS in JL channels is effectively reduced by screening, resulting in mobility comparable with the IM channels. The L4 electrons have higher mobility than L4' electrons. Applying uniaxial tensile strain along the channel can lower the energy of L4 valleys to enhance the channel mobility.