Nanorods for detecting ultraviolet light
doi:10.1038/nindia.2013.110 Published online 21 August 2013
Researchers have developed copper-doped zinc-oxide (ZnO) nanorods that have a high capacity for detecting ultraviolet (UV) light . The nanorods exhibited increased current flow when exposed to UV light, making them useful for fabricating different kinds of UV detectors.
ZnO is a versatile, tunable semiconducting material that is stable at high temperatures. Previous studies had shown that modified ZnO-derived nanowires can act as efficient UV detectors. However, preparation of such nanowires requires a complex growth process, which is expensive.
To devise a simple, cost-effective fabrication technique, the researchers synthesized ZnO nanorod arrays on glass substrates and then doped them with varying concentrations of copper using a technique known as hydrothermal method. To enable the UV-induced current to be measured, they deposited two gold contacts on the top surface of the nanorods.
On illuminating the nanorods with UV light, surface-bound oxygen molecules were released, generating a current of free electrons. In addition, charge carriers trapped by defects inside the nanorods were released on UV irradiation, increasing the UV-induced current. On turning the UV light off, oxygen molecules were re-adsorbed as superoxide ions, causing the photocurrent to drop rapidly.
The study revealed that the UV-induced photocurrent gain of copper-doped ZnO nanorods was two orders of magnitude higher that that of undoped ZnO nanorods. "These copper-modified nanorods will be useful for designing UV detectors for various fields, such as aerospace, military, environmental and biological applications," says Durga Basak, a co-author of the study.