“…The performance of MOSbased sensors can be improved by using semiconductor metal oxide nanomaterials as sensing material because the nanomaterials have a higher specific surface area, which increases the interaction between the sensing material and the target gas and, thus, improves the sensing response [1,2,4,5]. Metal oxide nanomaterials such as zinc oxide (ZnO), copper oxide (CuO), tin oxide (SnO2), tungsten oxide (WO3), nickel oxide (NiO), cobalt oxide (Co3O4), iron oxide (Fe2O3), titanium oxide (TiO2), indium oxide (In2O3), vanadium oxide (V2O5), molybdenum oxide (MoO3), and others are used to fabricate efficient MOS sensors [28][29][30][31][32][33][34][35][36][37]. To explore the characteristics of both, n-and p-type semiconductor nanomaterials, MOS sensors have recently been made using p-n heterojunction nanostructures, which employ composites of p-and n-type semiconductors as functional materials to improve sensing characteristics.…”