Electroluminescence from n-ZnO microdisks/p-GaN heterostructure

The light emitting diode structure based on p-GaN film/n-ZnO microdisks quasiarray heterojunction was fabricated. It is shown that the epitaxial quality of p-GaN films upon growth from the vapor phase can lead to growth of the hexagonal microdisk ZnO rather than the vertical nanorods. The density of the microdisks changed across the substrate surface. ZnO hexagonal microdisks are characterized by the average height of about 5 μm with diameters ranging from 25 μm up to 60 μm. The turn-on voltage of the heterojunction of ZnO/GaN (disks/film) is around 5 V. The diode-ideality factor was estimated to be of around 30. The large values of the ideality factors indicate a high density of trap states and also may be connected with the quality of the contacts to the p–n junction. The electroluminescence (EL) spectrum acquired from the p-GaN film/n-ZnO microdisks junction exhibited the bands with maxima at 366, 394 and 495 nm. On the basis of the data of X-ray diffraction, electrical and optical studies these peaks were associated with GaN near-band-edge (NBE) emission, ZnO NBE emission, and emission from the defect levels in ZnO, respectively.