Interfaces in piezotronic ZnO bicrystals: A TEM study upon segregation and properties of (0001) inversion boundaries
Piezotronic materials combine semiconducting and piezoelectric properties in order to tune potential barriers at interfaces like those present in zinc oxide varistor (variable resistor) ceramics. Therefore, zinc oxide has received renewed scientific interest and is considered a promising material holding potential for the development of novel devices, such as strain-triggered transistors, diodes or sensors. In this study, zinc oxide bicrystals with (0001) inversion boundaries were investigated using atomic resolution TEM methods and load dependent I-V measurements. Different synthesis methods were applied and their effect on the interface properties was studied with a special focus on the segregation behavior of bismuth, which is known to be an essential compound in ZnO varistors. Based on the TEM findings and the corresponding I-V measurements, a distinct correlation between interface coherency, degree of segregation and degree of non-linearity was observed. Since this correlation is attributed to basic principles of segregation and interfacial energy, the presented results are not only seen as a valuable contribution to the field of piezotronics and varistor ceramics, but also as adaptable for other material systems.