Low Leakage Current ZnO Nanowire Schottky Photodiodes Built by Dielectrophoretic Contact

This letter presents the characterization results of nanowire (NW) Schottky photodiodes fabricated from the dielectrophoretic contact between a ZnO NW and a Cu electrode. The device counter-electrode is fabricated using Pt focused ion beam deposition. The current-voltage characteristics exhibit rectifying properties with a leakage current as low as 40 pA at -40 V. The fitting of the forward characteristics reveals a barrier height lowering under UV illumination along with a large reduction of the series resistance. At forward bias, responsivities of ~10⁵ A/W are obtained above the bandgap energy. Under reverse bias, the responsivity reduces up to 10⁴ A/W, but a higher ultraviolet/visible contrast and a faster response are observed. In those conditions, the barrier height lowering is fostered by the drift of photogenerated holes toward the interface with the Cu electrode, yielding lower barrier height values under illumination.