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. Cathodoluminescence spectroscopy inside a scanning electron microscope correlates tip voltages directly with native point defect distributions of individual ZnO microwires in three dimensions. Spatial distributions of common Cu antisites in ZnO extending throughout their length correlate this defect's acceptor nature and distribution directly with piezoelectric potential, revealing how they can control the tip piezovoltage of ZnO microwire-based nanogenerators, identifying specific defects to increase device output, and suggesting growth and processing treatments to create these defects.