Ultraviolet electroluminescence of LED devices based on n-ZnO nanorods grown by various methods and p-GaN films

Abstract

Light emitting diodes (LEDs) structures based on p -GaN (cid:28)lm/ n -ZnO nanorods quasiarray heterojunction were fabricated. ZnO nanostructures were grown on the p -type GaN templates using two di(cid:27)erent methods. The turn-on voltages of ZnO/GaN heterojunctions based on ZnO nanorods grown using the gas-transport reaction and hydrothermal methods were equal to 3.2 V and 6.5 V, respectively. The diode-ideality factors were estimated to be of around 45 and 36 for the samples with ZnO nanorods grown using the method of the gas-transport reaction and the hydrothermal method, respectively. The large values of the ideality factors can be explained by a high density of trap states and quality of the contacts with the p − n junctions. The electroluminescence (EL) spectra of LEDs with ZnO nanorods grown by the gas-transport reaction and hydrothermal methods were approximated by four and three Gaussians, respectively. On the basis of the X -ray di(cid:27)raction (XRD), electrical and optical studies data, one can conclude that the emission peaks at 389(cid:21)391, 410(cid:21)412, 436(cid:21)438 and 502 nm correspond to the near-band-edge (NBE) recombination in ZnO, interface carriers recombination in ZnO/GaN junction, the electrons transition from GaN conduction band to Mg 2+ doping level, and to the emission from the defect levels in ZnO, respectively. The LED based on ZnO nanorods synthesized using the hydrothermal method emitted a more pure ultraviolet (UV) light.