Size dependence of surface-roughness-limited mobility in Silicon nanowire FETs

Low-field mobility in ultra-short nanotransistors is attracting large interest as strongly influenced by the role of quasi-ballistic carriers. Short-channel Silicon nanowire transistors (SiNWTs) are major candidates to work in this transport regime. Moreover, they are also expected to be strongly influenced by potential fluctuations arising from surface roughness (SR) at the Si-oxide interface. Here, we investigate the SR-limited mobility for such devices using a full-quantum transport model within the non-equilibrium Green´s functions (NEGF) formalism. This allows us to properly describe quantum phase coherence effects characterizing ballistic transport. Moreover the effects of SR on the mobility are evaluated exactly, by directly computing the effective mobility for several geometrical realizations of rough interfaces. Devices with different lateral section widths are analyzed showing the relevant transport mechanism impacting the mobility. An evaluation of their performances is carried out with direct reference to ballistic devices and substantial different results are found depending on the nanowire cross section.