Enhanced pressure response in ZnO nanorods due to spontaneous polarization charge

We present measurements of the induced charge flow when a compressive force is applied by contacting to a ZnO nanowire (NW). The measured charge transfer from the NW is over 104 times larger than expected from the strain-induced piezoelectric response, and is comparable in magnitude to the spontaneous polarization charge, associated with an ideal ZnO NW. A model is presented that compares the total energy of an isolated NW and external capacitor with the total energy when the capacitor and NW form a closed circuit. The analysis shows that it is possible, for realistic values of surface defect creation energy, to have spontaneous polarization charge transferred from a NW to an external capacitor when a circuit is completed between them. We propose that it is possible to use spontaneous polarization charge to get a significantly enhanced response in ZnO-based NW pressure sensors.