Schottky Diode Based on a Single Carbon-Nanotube-ZnO Hybrid Tetrapod for Selective Sensing Applications

In this work, a general strategy to change the selectivity of individual ZnO tetrapod (ZnO-T)-Schottky diode-based devices by hybridization with carbon nanotubes (CNT) is presented. A microscale Schottky diode based on Pt-nanocontacts to a single ZnO-T covered/hybridized with CNT, designated as ZnO-T-CNT, is fabricated and the temperature-dependent UV and gas sensing properties are investigated. The gas sensing investigations indicate that due to the presence of CNTs on the surface of the ZnO-T a higher NH3 response (factor of approximate to 90) at room temperature is observed, compared to H-2 gas response (approximate to 14). This effect is attributed to the excellent charge transfer between the CNTs and ZnO-T as well as NH3 molecule adsorption on the surface of the CNTs, which can efficiently reduce the Schottky barrier height. By increasing the operating temperature up to 150 degrees C (starting from 50 degrees C) the NH3 response is considerably reduced, leading to an excellent H-2 gas selectivity. In the case of H-2 gas, an increase in temperature up to 150 degrees C shows a considerably increase in gas response of about 140 (approximate to 10 times). Thus, this device offers the possibility to be used for selective detection of NH3 and H-2 by only changing the operating temperature. Furthermore, by using the developed strategy/approach other materials can be used for the fabrication of gas sensors with selectivity to other gases.