One-Dimensional ZnO/AlN Core-Shell Interface Design for Pure Ultraviolet Electroluminescence

Heterojunction is an alternative strategy to achieve pure ultraviolet electroluminescence (UV EL) in situation of p-type doping absence for ZnO homojunction. However, the most reported n-ZnO/p-GaN heterojunction device exhibited broad EL spectra, generally including blue emission from GaN, UV emission from ZnO, and blue-violet emission from ZnO/GaN interface. Herein, to realize pure UV EL of ZnO, one-dimensional ZnO/AlN core-shell structure was fabricated and then bonded with p-GaN to establish an n-ZnO/AlN/p-GaN heterojunction. In this device, the wide-bandgap AlN buffer was sputtered on the surface of the ZnO core as a shell layer, forming a suitable energy-band configuration with a high electron barrier to prevent electron injection from ZnO to GaN and a low valence band offset to keep hole injection from GaN to ZnO. Owing to the well-matched lattices of ZnO and AlN, a high-quality ZnO/AlN interface was established to block electrons more sufficiently. Meanwhile, the perfect ZnO/AlN core-shell structure resulted in the effective surface defect passivation, thus effectively improving the inter-band recombination of ZnO. After optimizing the AlN buffer width to 15.38 nm, the carriers recombination region was controlled significantly on the ZnO side, so that the heterojunction generated a pure UV EL, peaking at 382 nm with a narrow full width at half maximum of about 13 nm, which aligned perfectly with the photoluminescence of high quality ZnO.