Impact of Source to Drain Tunneling on the Ballistic Performance of Si, Ge, GaSb, and GeSn Nanowire p-MOSFETs

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 Ge
_0.96
Sn
_0.04
nanowire MOSFETs (NWFETs) were simulated at a scaled gate length (L
_G
) of 10 nm, 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, we simulated a set of six different transport/confinement directions, at a fixed OFF-state current (I
_OFF
) of 100 nA/μm and supply voltage V
_DD
= -0.5 V to identify the direction with the highest ON-current (I
_ON
). For Ge, GaSb, and GeSn [001]/110/1̅10 oriented NWFETs, with [001] being the direction of transport and 110, 1̅10 being the directions of confinement for the nanowire, 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]/110/1̅10 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. Our simulation result show that with properly chosen channel transport orientation and S/D doping concentration, performance of materials with high hole mobility can be optimized to reduce the impact of SDT and provide a performance improvement over Si-channel based p-MOSFETs.