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We fabricated and characterized ultraviolet (UV) light-emitting diodes (LEDs) composed of n-ZnO/SiO2-ZnO nanocomposite/p-GaN heterostructures. Significant UV electroluminescence at 387 nm from the n-ZnO layer in this heterostructure LED was observed at a forward-bias current of as low as 1.8 mA. This is ascribed to the high quality of the n-ZnO layer and the effective function of the SiO2-ZnO nanocomposite layer. The SiO2-ZnO nanocomposite layer accomplishes the role of current blocking by forming the larger energy barrier for electron injection from n-ZnO into p -GaN and also contributes to, due to its low refractive index, higher light extraction efficiency from the n-ZnO layer.