Silver Schottky contacts to Zn-polar and O-polar bulk ZnO grown by pressurized melt-growth method

The current transport mechanisms of Ag Schottky contacts to Zn-polar and O-polar bulk ZnO single crystals were investigated over the temperature range of 100300 K. Using the thermionic emission (TE) model, Schottky contacts to Zn-polar face were found to have higher barrier heights (lower ideality factors) than those to O-polar face. Compared to the theoretical value of n-type ZnO, the higher Richardson constant was obtained for both polar faces in the modified Richardson plot, indicating that the TE model, which considers barrier inhomogeneity, cannot adequately explain the current transport. Temperature-dependent tunneling characteristics showed that the tunneling current was dominant for the Zn-polar face over the entire temperature range (100300 K). For the O-polar face, the tunneling current was dominant mainly at low temperatures (100200 K) and the TE component contributed strongly to the current transport above 200 K.