In the present invention, there is provided semiconductor devices such as a Schottky UV photodetector fabricated on n-type ZnO and Mg.sub.xZn.sub.1-xO epitaxial films. The ZnO and Mg.sub.xZn.sub.1-xO films are grown on R-plane sapphire substrates and the Schottky diodes are fabricated on the ZnO and Mg.sub.xZn.sub.1-xO films using silver and aluminum as Schottky and ohmic contact metals, respectively. The Schottky diodes have circular patterns, where the inner circle is the Schottky contact, and the outside ring is the ohmic contact. Ag Schottky contact patterns are fabricated using standard liftoff techniques, while the Al ohmic contact patterns are formed using wet chemical etching. These detectors show low frequency photoresponsivity, high speed photoresponse, lower leakage current and low noise performance as compared to their photoconductive counterparts. This invention is also applicable to optical modulators, Metal Semiconductor Field Effect Transistors (MESFETs) and more.