The electrical properties of Ag Schottky contacts to hydrothermally-grown polar (Zn- and Opolar) and nonpolar (m-plane) bulk ZnO were investigated. Ohmic-like behavior for Zn-polar ZnO and rectifying behaviors for O-polar and m-plane ZnO were observed from current-voltage (I-V) measurements. Schottky contacts to O-polar ZnO were found to have higher barrier heights and lower ideality factors than those to m-plane ZnO. Higher series resistances were found for both the Zn-polar and the m-plane ZnO compared to the O-polar ZnO probably due to the presence of the interfacial layer and interface states. The homogeneous barrier heights obtained from linear fitting to the effective barrier height vs. ideality factor plots were similar to those obtained from capacitance-voltage (C-V) measurements. A higher degree of oxidation at the Ag-ZnO interface might occur for O-polar ZnO than for m-plane ZnO, increasing the barrier heights. The large dispersion in the capacitance for m-plane ZnO was related to the excess capacitance due to the interface states.
- Barrier heights
- Excess capacitance
- Hydrothermally-grown bulk ZnO