Contact-controlled sensing properties of flowerlike ZnO nanostructures

Contact-controlled sensing is realized from flowerlike ZnO structures composed of rods. The rods are around 150 nm in diameter and up to a few micrometers in length. When they are exposed to air, a depletion region formed below the surface of the rods arising from the adsorption of oxygen. Surface depletion does not greatly reduce either the carrier density or the mobility in the rods but significantly modify the potential barrier of the contacts between the rods. Both the large diameter and the long length result in a low sensor resistance down to $104\mathrm{k}\Omega$ in air at 300 °C. The exponential increase of the tunneling rate with the thickness and height of the contact barrier leads to a high sensitivity up to 14.6 for 100 ppm ethanol. These results indicate that contact-controlled sensing can be used to fabricate high-performance sensors with both high sensitivity and low resistance.