Effect of oxygen plasma treatment on the electrical properties in Ag/bulk ZnO Schottky diodes

Using current-voltage (I-V) and capacitance-voltage (C-V) measurements, the effect of oxygen plasma treatment on the electrical properties of Ag Schottky contacts to hydrothermally-grown O-polar bulk ZnO was investigated. Schottky contacts to untreated ZnO had higher barrier heights and lower ideality factors than those to oxygen plasma treated ZnO. The measured C-V and conductance-voltage (G/ω-V) characteristics for both samples showed strong dependences on bias voltage and frequency. The increments of series resistance in small forward bias region (0-0.5 V) was larger for oxygen plasma treated ZnO, indicating that the contribution of interface states to series resistance was more significant. The interface state density was obtained from the corrected C-V and G/ω-V characteristics with considering series resistance. The higher interface state density was found for oxygen plasma treated ZnO, implying that oxygen plasma induced the interface states near the ZnO surface.