Utilizing mechanical strain to modulate electronic transport processes across electrostatic potential barriers is an encouraging concept for the design of multifunctional electronic devices like strain triggered transistors, diodes and strain sensors with enhanced performance. The interplay between stress induced piezoelectric charges and the electronic band structure at semiconductor interfaces, i.e. the piezotronic effect was proposed by Z.L. Wang et al. in 2006 with their work on ZnO-nanowire-metal junctions.
In our work, we utilize the concept of piezotronics, to modulate the height of double Schottky barriers present at doped ZnO-ZnO grain boundaries. In polycrystalline varistor ceramics, a change in conductivity by several orders of magnitude can be observed under the application of a mechanical load. This results in a high stress sensitivity, expressed in a gauge factor exceeding values of 1000. Furthermore, we utilize doped ZnO bicrystals as model system to study the polarity dependence of the piezotronic effect. Doped ZnO bicrystals are prepared ether in head-to-head (O|O) or tail-to-tail (Zn|Zn) orientation with electrical properties typical for individual double Schottky barriers in varistor ceramics. By changing the bicrystal interface from O|O- to Zn|Zn-termination, a uniaxial compressive load results in a pronounced decrease or increase of the potential barrier height, respectively. Hence, it is possible to fully exploit the piezotronic potential of individual double Schottky barriers and to validate and extend the theoretical concept of varistor piezotronics.