First-principles simulation on wire diameter dependence of piezoresistivity in zinc oxide nanowires

Abstract

The wire dependence of piezoresistivity in wurtzite-type zinc oxide (ZnO) nanowires with a 〈0001〉 orientation has been simulated on the basis of the first-principles calculations of model structures. The strain responses to the carrier conductivity of n- or p-doped semiconducting wurtzite-ZnO〈0001〉 nanowire models were calculated using band carrier densities and their corresponding effective masses derived from a one-dimensional band diagram by our original procedure. In this simulation, the conductivities of p-doped thin nanowire models change drastically owing to a longitudinal uniaxial strain because of either the redistribution of holes among subbands with completely different effective masses or the change in the effective mass. As a result, high positive longitudinal gauge factors and piezoresistance coefficients were obtained. On the other hand, for thick nanowire models with wire diameters of more than 1.5 nm, the piezoresistivity of the nanowire itself is essentially low in both the n- and p-doped states.