Piezo-Semiconductor Coupled Model for the Simulation of Zinc Oxide 1-3 Piezo-Composite

Semiconducting effects in zinc oxide nanowires-based nanogenerators greatly impact their performances. A coupled model integrating piezoelectric and semiconducting properties is developed with a finite element method to better understand the phenomena involved in this kind of device made with a process including chemical bath deposition of the nanostructures and their polymer encapsulation. Free carriers and surface traps are taken into account to give some keys to explain differences between previous theoretical and experimental works. This model is first validated on a single nanowire with a 1016 cm-3 n-doping level by comparison with analytical calculations. For this comparison, surface traps are not taken into account as no analytical solution is available considering them. Second, n-doping levels (between 1012 and 1018 cm-3) and surface traps densities (between 108 and 1012 cm-2) lead to variations of the generated piezopotential of two orders of magnitude. The control of these two semiconducting properties is a real challenge for this kind of application. Furthermore, simulation results show that the benefic effect of 1-3 piezo-composite is still present even for a high n-doping level of 1018 cm-3. A model for Finite Element Method is proposed for nanogenerator and energy harvesting. This model couples both piezoelectric and semiconducting phenomena using a bidirectional way to solve the relative equations. Thanks to this model, the influence of the free charge carriers and the surface traps is directly added to all key parameters like the energy level of the traps.image