Ge-doped ZnO nanowire arrays as cold field emitters with excellent performance.

Elemental doping is an efficient strategy to modify the electronic and optoelectronic properties of semiconductor materials. In this work, a high-quality Ge-doped tapered ZnO nanowire array was prepared via a simple chemical vapor deposition approach. The I-V and light emission behaviors were investigated based on a single nanowire with good electrical conductivity. The Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy characterizations indicate that the doped nanowires possess a largely reduced work function relative to that of the pure ZnO nanostructures. These advantages allow Ge-doped ZnO nanowire arrays to deliver excellent field emission performance, including low turn-on and threshold fields, high emission current and long-term stability.