ZnO-Based Fairly Pure Ultraviolet Light-Emitting Diodes With a Low Operation Voltage

A ZnO-based metal-insulator (HfO
₂
) -semiconductor diode was synthesized on a commercially available n
⁺
-GaN/sapphire substrate using a radio-frequency magnetron sputtering system. Electroluminescence measurements revealed that the diode exhibited fairly pure ultraviolet (UV) emission peaking at ~ 370 nm with a line width of less than 8 nm. By choosing a proper thickness of the insulator HfO
₂
layer, the threshold voltage of the emission could be reduced to 2 V, demonstrating that this ZnO-based fairly pure UV light-emitting diode can be driven by two ordinary dry batteries. The reason for low threshold voltage is proposed in terms of the n
⁺
-GaN/sapphire substrate and the high-
k
insulator HfO
₂
layer.