Influence of external electric field on piezotronic effect in ZnO nanowires

In this work, the piezotronic effect is investigated for the first time in external electric fields ranging from 0 V.cm(-1) to 2,000 V.cm(-1) by using n-type ZnO nanowires supported by a flexible substrate. In the presence of an external electric field, the Schottky barrier height (SBH) is lowered by the image force, allowing more free carriers to pass through the metal-semiconductor junction and enhancing the screening effect on positive piezoelectric polarization charges. As the strength of the external electric field increases, the piezotronic effect is significantly suppressed and the metal-semiconductor contact finally exhibits Ohmic behavior. The experimental results show that devices can be classified into three groups, corresponding to low, moderate, and high carrier densities of the nanowires used. This work not only helps us to explicate the basic physical mechanism of the piezotronic effect in a harsh environment in an electric field but also provides guidelines for future design and fabrication of piezotronic devices.