Enhanced ultraviolet emission in photoluminescence of GaN film covered by ZnO nanoflakes

► ZnO nanoflakes cap layer was synthesized on GaN film via a thermal oxidation process. ► PL results show the UV emission of GaN largely enhanced with ZnO NFs cap layer. ► Low oxidation temperature obtained high density of NFs and high UV emission peak. ► The super UV photodetector was obtained with low temperature cap layer at 470 °C. ► The increase in oxidation temperature of the ZnO limited the increase of UV emission of GaN.