Nanopiezotronics and nanogenerators

Abstract

Today's nanoelectronics rely on the transport of charge carriers under the driving of externally applied voltage to perform specific functionality, such as transistors and diodes. Recently, Piezotronics was introduced as a new field in nanoelectronics[1,2]. It utilizes the coupled piezoelectric and semiconducting property of nanowires (NWs) and nanobelts (NBs) for designing and fabricating electronic devices such as transistors and diodes. Piezoelectricity is a coupling between a material's mechanical and electrical behavior. When a piezoelectric crystal is mechanically deformed, the positive- and negative-charge centers are displaced with respect to each other. Therefore, while the overall crystal remains electrically neutral, the difference in charge center displacements results in an electric polarization within the crystal. Electric polarization resulting from mechanical deformation is perceived as piezoelectricity. Once the piezoelectric materials are also semiconductors, such as ZnO, their electronic characteristic can be affected by the piezoelectric potential. This phenomenon becomes more obvious when the crystal size is in nanometer regime and so it is also called nano-Piezotronics. It is anticipated to have a wide range of applications in electromechanical coupled sensors and devices, nanoscale energy conversion for self-powered nanosystems, and harvesting/recycling of energy from environment. In this chapter, ZnO, as a typical and widely studied piezotronic material, is reviewed in detail from the origin of its piezoelectric property to the novel nanodevices made from piezotronic ZnO NWs.