Simulation of enhanced hole ballistic velocity in asymmetrically strained Germanium nanowire trigate p-MOSFETs

The impact of asymmetric strain in Ge nano wire (NW) trigate p-MOSFETs with record measured hole mobility [1] is simulated. Contrary to previous studies of uniaxial and biaxial strain, the impact of very large (2.4%), non-uniform asymmetric strain (achieved by patterning-induced lateral relaxation) is studied through NW simulations. Asymmetric strain significantly warps the valence band (VB), reducing the hole effective mass in the transport direction, and increasing the ballistic velocity (ν_θ ∝ √m* [2], [3]) compared to biaxial strain. Consistent with previous mobility measurements [1], analysis of the VB strucuture reveals a 1.6× increase in the inverse effective mass for a 49-nm wide asymmetrically-strained Ge NW compared to planar biaxially strained Ge (s-Ge) with 2.4% compressive strain. ν_θ improves in narrow NWs due to lateral strain relaxation that reduces the transport effective mass. A ν_θ enhancement of 2.8X relative to unstrained Si (1.6× relative to 1% uniaxially strained Si) is predicted for 10-nm wide s-Ge NWs suggesting a scalable transport enhancement technique for future technology nodes.