STRUCTURAL INVESTIGATION OF n-ZnO/p-GaN ULTRAVIOLET LIGHT-EMITTING DIODES GROWN BY ATOMIC LAYER DEPOSITION

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- Al 2 O 3 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 .