Hall effect, photoluminescence, and Schottky diode measurements were made on the Zn-polar and O-polar faces of undoped, bulk, single crystal, c-axis ZnO wafers. Significant polarity related differences were observed in the PL and Schottky diode characteristics of low carrier concentration, hydrothermally grown wafers. Increased emission from free exciton recombinations and from recombinations between 3.3725 and 3.3750 eV was observed on the Zn-polar face. Conversely, emission between 3.3640 and 3.3680 eV was more intense on the O-polar face. The barrier heights of silver oxide Schottky diodes were approximately 130 meV larger on the Zn-polar face compared to the O-polar face.