Mechanically tunable conductivity in piezoelectric semiconductors

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The unique electrical properties in varistors and diodes rely on doping and interfacial potential barriers which are permanently implemented into the device. Here we provide a fundamentally new approach, geared towards piezoelectric semiconductors in which an interfacial electrostatic potential barrier can be reversibly tuned through external mechanical stress. The concept is related to piezotronics that so far has been focused, however, on Schottky barriers in nanofibers and yielded only small changes of potential barrier heights.This novel concept is fundamentally investigated using ZnO as semiconductor with high piezoelectric coefficient. The focus will be on single (ZnO/metal) and double (ZnO/ZnO) Schottky barriers with well determined orientations utilizing ZnO single crystals. Tailoring is then afforded using grain conductivity of the ZnO, work function of the metal and interface states determined by grain boundary misorientation and interface dopants. The additional flexibility arises due to the application of interfacial stresses during electric loading. Electrical characterisations in collaboration with other projects will be on density of electron states and electron mobility, in terms of impedance spectroscopy and I V curves at different frequency and temperature. A special challenge lies in the dichotomy of stress-tuned interfacial charge and semiconductor conductivity-enticed charge screening. At the same time, this project will provide polycrystalline ZnO to aid validation of modelling projects and affords electromechanical characterisation of polarisation texture of ZnO.