STRUCTURAL INVESTIGATION OF n-ZnO/p-GaN ULTRAVIOLET LIGHT-EMITTING DIODES GROWN BY ATOMIC LAYER DEPOSITION
Abstract
Electron microscopy investigation has been carried for an n-ZnO/p-GaN:Mg heterojunction ultraviolet (UV) light-emitting diode device, where the n-ZnO layer was grown by atomic layer deposition on the p-type GaN:Mg/undoped GaN structure prepared on c-Al2O3 substrate. Threading dislocations, formed at the interface of the GaN/Al2O3, disappeared at the interface of n-ZnO/p-GaN during post-deposited rapid thermal annealing and accordingly the n-ZnO layer became an almost perfect single crystal including only a few surviving dislocations. An interfacial layer was found along the (0001) interface between the n-ZnO and p-GaN:Mg layers. Scanning transmission microscopy analysis revealed that the interfacial layer was composed of ZnO crystal, which connected coherently with the neighboring n-ZnO and p-GaN:Mg. This interfacial layer contained a few atomic percents of Mg, the atoms of which had been diffused from the p-GaN:Mg. The high quality crystalline n-ZnO and the interfacial layer forming a ZnO/GaN interface states are responsible for the UV electroluminescence from the ZnO.
