Finite element simulations on piezoelectric modulation of ZnO grain boundary barrier height

Abstract

Modeling grain boundary potential barriers in ZnO is complicated, because the physical mechanism for barrier development and its modification by external influence factors are complex. It has been shown that the barrier height can be significantly modulated by mechanically induced piezoelectric charge. This makes ZnO-ZnO interfaces suitable for advanced piezotronic systems, in which conductivity is modulated by mechanical stress. However, in order to apply this effect, the ability to tailor the interfaces and an accurate physical description of the piezoelectric impact are necessary. In this work, a finite element (FE) model was developed to provide such a description. Due to its full mechanical-electrostatic coupling, this model requires few prior assumptions about the free spatial charge, enables multidimensional study, and allows access to quantities such as charge, energy, and electric field distributions. Moreover, the FE model inherently includes inverse piezoelectric and anisotropy effects, which are shown to have a large impact on barrier height. Additionally, it is illustrated that this model can be used for advanced 3D microstructure simulations taking the complexity of the interface properties into account.