First-principles study on the piezoresistive effect of Ge/Si core/shell Nanowires

We have simulated the piezoresistance coefficients (Pie Coefficients) in some certain Germanium nanowire (GeNW), Silicon nanowire (SiNW) and several Ge/Si core/shell nanowires based on the first-principles calculations. All the nanowires are with a same diameter in <;111>; direction and remain unsaturated on surface. In these <;111>; nanowires, It was found that the Pie Coefficients of the SiNW and the Ge₁Si₃ (Ge/Si core/shell nanowire with three layers of silicon atoms) can reach as much as 35.26 × 10^-11Pa^-1 and 30.0 × 10^-11Pa^-1 under 2.5% tension in the longitudinal direction. And all those of the GeNW and the Ge₃Si₁ (with only one silicon atom layer) almost kept negative values from -1 × 10^-11 Pa^-1 to -9 × 10^-11 Pa^-1, whether under compressions or tensions. However, under compressions, the Ge₂Si₂ (with two layers of silicon atoms surrounded outside) almost had no piezoresistive effect.