White-Light-Emitting Diode Based on ZnO Nanotubes

We report the fabrication and electroluminescence of a simple ZnO nanotube diode. The hexagonal ZnO nanotubes are synthesized electrochemically using a two-step method. At low forward bias, the electroluminescence spectrum of the ZnO nanotube diode exhibits a traditional emission spectrum composed of an excitonic peak centered at 400 nm and a broad-band emission at around 550 nm, consistent with its photoluminescence spectrum. When a higher voltage is applied, the diode current grows rapidly and the spectral coverage broadens to include almost the entire visible spectrum. The electroluminescent intensity of the ZnO nanotube diode is much stronger than that of the ZnO nanorod diode.