Band structure and mechanism of semiconductor metal oxide heterojunction gas sensor

Gas sensors play a major role in chemical industries, food processing units, pharmaceutical industries, health monitoring devices through breath analysis, domestic, and environmental monitoring for human safety. Metal oxide chemiresistive gas sensor transmits target gas details into electrical signals based on the adsorption/desorption of gases. In metal oxide semiconductor gas sensors, the sensitivity and selectivity can be improved by doping, functionalization, composites, heterojunction formation, and morphological modification. Heterojunction formation improves the efficiency of the sensing material through the synergetic effect, enhancing the adsorption rate, accelerating catalytic activity, and electron/hole depletion interface. Also, heterojunction with heterostructured nanomaterials has a significant effect on the sensing performance and detection speed. Here, the band structure of heterojunction, sensing mechanism of p-n, n-n, and p-p heterojunctions are well discussed, and various heterojunction materials are demonstrated for the detection of different gases. MXene is a blooming 2D nano material in gas sensors that possesses high surface area, rich functional group, high metallic conductivity, and more active sites for the adsorption of target gases. Poor stability and selectivity of MXene could be altered through heterojunction formation with metal oxides. We also discussed the MXene heterojunction with metal oxides for the detection of various gases.