Mobility Calculation of Ge Nanowire Junctionless and Inversion-Mode Nanowire NFETs With Size and Shape Dependence

The electron mobility in junctionless (JL) and inversion-mode (IM) Ge nanowire nFETs with [110] channel direction is studied by theoretical calculations. Channels with different widths and cross-sectional shapes are compared. The mobility calculation is based on the Kubo-Greenwood formulation for 1-D systems. Phonon scattering, Coulomb scattering (CS), and surface roughness scattering (SRS) are considered. With the equivalent oxide thickness of 1 nm, diamond and square channels have the higher mobility than circular channels at low channel carrier density, but the lower mobility at high channel carrier density for both JL and IM channels. This mobility trend is explained by the SRS on the sharp corners in diamond and square channels. The JL channels have the lower mobility than IM channels at low channel carrier density due to additional CS. At high channel carrier density, SRS dominates, and the JL channel has the slightly higher mobility than the IM channel due to its weaker SRS. The mobility difference between JL and IM is negligible for 5-nm narrow wires.