High-performance piezophototronic devices based on zinc oxide nanostructured thin films synthesized by physical vapour deposition

This work analyzes the piezophototronic effect in zinc oxide (ZnO) thin films deposited by a physical vapour deposition (PVD) technique, studying changes in the piezoelectric coefficient (d33) as a function of ultraviolet (UV) light radiation. The piezophototronic effect comprises the coupling of piezoelectricity, semiconductor behaviour and photoexcitation in piezoelectric materials. This effect has been conventionally studied in piezoelectric thin films subjected to an external mechanical stress, where the piezo-charges generated by the mechanical stress induced at both ends of the piezoelectric material, are able to control the piezo-potential of electric contacts or energy levels in p-n junctions. In this regard, the external stress applied to a piezoelectric material is able to control the process of carrier injection, transport and recombination, allowing the improvement of the efficiency in optoelectronic devices. However, the study of the piezoelectric properties of thin film materials, such as ZnO, as a function of light exposure has not been explored yet. This work presents a thorough analysis on the d33 of ZnO thin films measured by quasi-static or Berlincourt method as a function of the excitation UV light conditions. Structural, optical and electrical properties of the films were also analyzed. This work also covers the exploration of this new piezophototronic device as an active layer in sensing platforms and energy harvesting devices.