Polarization-induced enhancement of hole injection efficiency in n-ZnO/p-graded AlxGa1-xN heterojunction diodes

摘要

Vertically aligned O-polar ZnO nanowall networks were prepared on N-polar p-graded AlxGa1-xN/sapphire substrates by metal-organic chemical vapor deposition. Further, heterojunction light-emitting diodes based on O-polar n-ZnO/N-polar p-graded AlxGa1-xN were fabricated. A strong and narrow ultraviolet emission at 388 nm, originating from ZnO, was observed under forward bias. The hole injection efficiency of the proposed diode was significantly enhanced owing to the existence of polarization-induced two-dimensional hole gas at the n-ZnO/p-graded AlxGa1-xN heterointerface, thereby yielding an enhanced light output power. This work provides an alternative path towards the realization of highperformance ZnO-based ultraviolet diodes. (C) 2016 The Japan Society of Applied Physics