Low-Temperature Growth of SnO2 Nanorod Arrays and Tunable n-p-n Sensing Response of a ZnO/SnO2 Heterojunction for Exclusive Hydrogen Sensors

Uniform SnO2 nanorod arrays have been deposited at low temperature by plasma-enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO2 nanorod sensor to H2 gas. The ZnO-modified SnO2 nanorod sensor shows a normal n-type response to 100 ppm CO, NH3, and CH4 reducing gas whereas it exhibits concentration-dependent n-p-n transitions for its sensing response to H2 gas. This abnormal sensing behavior can be explained by the formation of n-ZnO/p-Zn-O-Sn/n-SnO2 heterojunction structures. The gas sensors can be used in highly selective H2 sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification. Uniform SnO2 nanorod arrays have been deposited by PECVD and highly selective H2 sensors are fabricated by ZnO surface modification of the SnO2 nanorod arrays. Concentration-dependent n-p-n transitions for the sensing response to H2 gas in the range of 10-3000 ppm are observed owing to the formation of n-ZnO/p-Zn-O-Sn/n-SnO2 heterojunction structures