Native Point Defects Controlling Piezoelectric Voltage in Strained ZnO Microwires.

Piezovoltages generated by ZnO nano/microwire bending and strain enable electronic biogenerators that harvest human body movement to power-implanted biomedical devices. Currently, low voltages generated by these biogenerators limit their use to replace today's biomedical batteries. Electrically charged native point defects inside ZnO microwires can control these macroscopic piezo voltages, generating transverse electric fields that couple with strained wires' lengthwise piezoelectric fields so they redistribute spatially and change voltage output.

Electric Field Manipulation of Defects and Schottky Barrier Control inside ZnO Nanowires.

We directly measure the three-dimensional movement of intrinsic point defects driven by applied electric fields inside ZnO nano- and micro-wire metal-semiconductor-metal device structures. Using depth- and spatially resolved cathodoluminescence spectroscopy (CLS) in situ to map the spatial distributions of local defect densities with increasing applied bias, we drive the reversible conversion of metal-ZnO contacts from rectifying to Ohmic and back. These results demonstrate how defect movements systematically determine Ohmic and Schottky barriers to ZnO nano- and microwires and how they can account for the widely reported instability in nanowire transport.