ZnO films were grown on c-plane sapphire by dc reactive magnetron sputtering. X-ray diffraction measurements showed that an epitaxial relationship of ZnO[10 (1) over bar0]parallel toAl(2)O(3)[11 (2) over bar0] and ZnO[2 (1) over bar(1) over bar]parallel toAl(2)O(3)[1 (1) over bar 00] was maintained down to a substrate temperature T-s approximate to 80degreesC, corresponding to < 17% of the ZnO melting point. The low-temperature epitaxy was explained by the energetic species produced during sputtering and a high mobility of Zn surface atoms in low-oxygen conditions. Crystalline perfection improved with increasing T-s, decreasing growth rate, and decreasing oxygen-to-zinc flux ratio. Dense microstructures with flat surfaces were achieved at T-s approximate to 200degreesC, although it T-s approximate to 80degreesC films tended to transition to a columnar Zone 1 microstructure from a Zone T microstructure with increasing film thickness. In general, T-s=200-300degreesC and an oxygen-to-zinc flux ratio of approximate to300 yielded a favorable combination of good optical transparency, crystalline perfection, flat surfaces, and dense microstructure. (C) 2004 American Vacuum Society.