Electrical properties of An and Ag Schottky diodes prepared on epiready (0001)Zn surfaces of bulk n-ZnO crystals with electron concentration close to 10(17) cm(-3) were studied after various surface cleaning treatments. The lowest reverse currents were obtained with simple cleaning of the surface in organic solvents while additional etching of the surface in concentrated HCl or HNO3. substantially increased the reverse current without giving any clear advantages in the ideality factor of the forward current-voltage characteristics or. in the accuracy of capacitance-voltage characteristics and deep level spectra measurements. The properties of both the Au and the Ag Schottky diodes were seriously degraded by heating them in vacuum to temperatures higher than about 365 K but the mechanisms of degradation seem to be different for the two metals. (C) 2003 American Vacuum Society.