Piezotronic effect at Schottky barrier of a metal-ZnO single crystal interface

Abstract

ZnO is considered as one of the most promising semiconductor materials for future applications based on the piezotronic effect. Intense studies on ZnO nanowires had been carried out to understand the modulation of the Schottky barrier height at the metal ZnO interface via piezoelectricity. However, an experimental investigation on bulk ZnO single crystals and a fundamental comparison of the modification of the barrier height determined experimentally and theoretically are still missing. Therefore, an adjustment of the electrostatic potential barrier height at metal-ZnO single crystal interfaces due to stress induced piezoelectric charges was conducted, using both O- and Zn-terminated surfaces. In-situ stress dependent impedance and current-voltage measurements were utilized to extract the electrical properties of the potential barrier and to determine the reduction of the barrier height. The decrease of the interface resistance and increase of the capacitance reveal the presence of stress induced piezoelectric charges. The experimentally evaluated reduction of the barrier height reveals a moderate change of about 9 meV at 70 MPa and supports prior work on metal-ZnO nanowires. This change was found to be in good agreement with theoretical calculations based on the imperfect screening model if a thickness of the interface layer is assumed to be ∼2 Å.