Thermal stability of oxidized noble metal Schottky contacts to ZnO

Thermally stable oxidized palladium (PdOx, x=1.4) and oxidized iridium (IrOx, x=1.9) Schottky contacts (SCs) that showed strong rectification at 180 °C were fabricated on the Zn-polar (0001) face of hydrothermally-grown single crystal ZnO wafers, using reactive rf sputtering and reactive eclipse pulsed laser deposition, respectively. These PdOx and IrOx SCs were highly rectifying with effective barrier heights of 1.25 eV and 1.02 eV, respectively, more than 12 orders of magnitude of room-temperature current rectification (at biases of ±2.0 V), and were almost 'ideal' with ideality factors of 1.03 and 1.02, respectively, that were very close to the image-force-controlled limit for laterally homogeneous contacts. The strong rectifying performance of these SCs was maintained at 180 °C, with current rectification in excess of 7 and 6 orders of magnitude for the PdOx and IrOx SCs, respectively, indicating their suitability for high temperature applications. Current-voltage characteristics over the temperature range 20-180 °C were used to extract Richardson constant values of 39±15 Acm−2K−2 and 9±1 Acm−2K−2 for the PdOx and IrOx SCs, respectively, close to the theoretical value of 32 Acm−2K−2.