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.