Mobility calculation of Ge nanowire junctionless NFETs with size and geometry dependence

The channel cross section geometry and size dependence of the electron mobility in Ge nanowire nFETs is studied by theoretical calculations for devices beyond the 7nm node. circular channels have the highest mobility for wide channels (width>7nm) operating at high overdrive voltage (>0.5V). While diamond-shaped channels have the highest mobility for wide channels operating at low overdrive voltage (<0.3V) and narrow channels (width<7nm). This is attributed mainly to the different surface roughness scattering at different channel conditions. Our calculation framework is based on Boltzmann transport and has been verified with the electron mobility extracted from the experimental data of junctionless nanowire nFET devices.