A series of Mg Zn O alloy films were grown on m-plane sapphire by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). Optical and structural characterizations indicated that the films with Zn mole fraction up to 55% are single-cubic-phased, and the optical bandgap of Mg Zn O film is 4.7 eV. The epitaxial relationships between substrate and rocksalt MgZnO layers were determined as (110) ∥(101̄0) , [001] ∥ [12̄10] , and [1̄10] ∥[0001] . The fixed uniform orientation of the films was accompanied by an improvement in crystal quality. A metal-semiconductor-metal structured solar-blind ultraviolet detector fabricated on Mg Zn O film showed a response peak at 260 nm and a sharp cutoff at 278 nm.