First-Principles Study on Piezoresistance Effect in Silicon Nanowires

We have simulated the piezoresistance coefficients in single-crystal silicon nanowires (SiNWs) on the basis of first-principles calculations of model structures. The carrier conductivity along the wire axis has been calculated using band carrier densities and their corresponding effective masses derived from the one-dimensional band diagram by a novel approach for a small amount of carrier occupation. In the <001> SiNW model, the uniaxial tensile stress to the longitudinal direction causes a sharp drop in the band energy of the highest valence band, leading to the redistribution of holes to other valence bands with a huge hole effective mass. The sudden change in the hole occupation with the increase in effective mass will bring a drastic decrease in the hole conductivity. We have obtained a giant longitudinal piezoresistance coefficient of 147 ×10 -11 Pa -1 for the p-type <001> SiNW. It is found that p-type <001> SiNW will be one of the most suitable candidates for nanoscale piezoresistors due to its giant piezoresistivity.