Preparation and study of ammonia gas sensor based on ZnO/CuO heterojunction with high performance at room temperature

An ammonia (NH3) gas sensor based on ZnO/CuO (ZC) heterojunction was prepared by hydrothermal method and the sensing mechanism was studied by first principle calculations based on density function theory (DFT). Experiments show that NH3 sensor based on ZC heterojunction has low detection limit (0.39 ppm), fast response/recovery time (2.3 s/2.1 s), high sensitivity, good selectivity, strong stability and high humidity resistance at room temperature (RT). Compared with ZnO, ZC has more oxygen free radicals appeared on surface of heterojunction, and has redox reactions with NH3 molecules to release more electrons to improve sensitivity of ZC. Calculations show that excellent performance is mainly due to the strong adsorption energy of ZC heterojunction to NH3 detection. The polarity of NH3 molecules is enhanced under strong built-in electric field formed by ZC heterojunction which absorbs more NH3 molecules to react with oxygen radicals on surface of ZC and induce high response of ZC to NH3 molecules. This study indicates that ZC heterojunction structure can effectively improve ZnO sensors for NH3 detection at RT, which is helpful for application of metal oxide semiconductor.