Low-threshold pure UV electroluminescence from n-ZnO:Al/i-layer/n-GaN heterojunction

► UV electroluminescence of n-ZnO:Al/i-layer/n-GaN heterojunctions has been obtained. ► Under positive voltage, a dominant UV emission peak around ∼370 nm is observed for both heterojunctions. ► The UV emission peak intensity of the heterojunction with i-MgO layer is much stronger than that with i-ZnO layer at the same voltage. ► The threshold voltage of n-ZnO:Al/i-MgO/n-GaN heterostructured device is as low as 2.3 V.