UV-free red electroluminescence from the cross-connected p-ZnO:Cu nanobushes/n-GaN light emitting diode

A p-ZnO:Cu/n-GaN heterojunction light emitting diode (LED) is fabricated by growing cross-connected p-ZnO:Cu nanobushes on n-GaN film using chemical vapor deposition under oxygen-rich condition. This LED emits stable UV-free red light of 677 nm and 745 nm. The electroluminescence (EL) light of this LED is tuned from ultraviolet (UV) of ZnO/GaN to UV-free red by the electronic interfacial transition from the conduction band of n-GaN to the deep acceptor levels of p-ZnO:Cu. Both room temperature and low temperature (5K) photoluminescence spectra of ZnO:Cu indicate that the UV emission of ZnO is suppressed and the green emission is enhanced, which implies the formation of Cu-related deep levels introduced by intentionally doping Cu in ZnO. These deep levels help the EL red emission in the LED device.