ULTRAVIOLET ELECTROLUMINESCENCE OF LED DEVICES BASED ON n-ZnO NANORODS GROWN BY VARIOUS METHODS AND p-GaN FILMS

Light emitting diodes (LEDs) structures based on p-GaN film/n-ZnO nanorods quasiarray heterojunction were fabricated. ZnO nanostructures were grown on the p-type GaN templates using two different 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 diffraction (XRD), electrical and optical studies data, one can conclude that the emission peaks at 389-391, 410-412, 436-438 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 Mg2+ 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.