  We investigated the effect of material choice and orientation in limiting
source to drain tunneling (SDT) in nanowire (NW) p-MOSFETs. Si, Ge, GaSb, and
Ge0.96Sn0.04 nanowire MOSFETs (NWFETs) were simulated using rigorous ballistic
quantum transport simulations. To properly account for the non-parabolicity and
anisotropy of the valence band the k.p method was used. For each material, a
set of six different transport/confinement directions were simulated to
identify the direction with the highest ON-current (ION ). For Ge, GaSb, and
GeSn [001]/110/-110 oriented NWFETs showed the best ON-state performance,
compared to other orientations. Our simulation results show that, despite
having a higher percentage of SDT in OFF-state than silicon, GaSb
[001]/110/-110 NWFET can outperform Si NWFETs. We further examined the role of
doping in limiting SDT and demonstrated that the ON-state performance of Ge and
GeSn NWFETs could be improved by reducing the doping in the source/drain (S/D)
extension regions. Finally, we analyzed the impact of increased injection
velocity in [ [001]/110/-110 oriented GaSb and GeSn NWFETs, as a result of the
application of uniaxial compressive stress, and showed that when compared at a
fixed OFF-current (IOFF) with unstrained NWFETs, uniaxial compressive stress
deteriorates the ON-state performancedue to an increase in OFF-state SDT
current component.
