The authors investigated the evolution of surface morphology of AlN films grown on ZnO substrates at low temperature (LT) (400 degrees C) as a function of anion/cation supplying ratio (V/III ratio). Unlike the well-known favorable growth conditions for high-temperature growth, smooth-surface LT-AlN layers were obtained under the O-polar surface, stoichiometric, and N-rich conditions. LT-AlN layers revealed smooth surface (roughness in root mean square=0.20 nm for AlN on O-polar ZnO and 0.44 nm for AlN on Zn-polar ZnO) and quite low etch-pit density (similar to 2 x 10(6) cm(-2) for AlN/Zn-polar ZnO). (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3264479]