Enhanced Room-Temperature NO2 Detection Using ZnO/SnO2/CdS Tri-Layer Heterostructure

Abstract

The trilayer, ZnO/SnO₂/CdS heterostructure was deposited on p-type silicon (p-Si) substrate by spray pyrolysis for application in NO₂ gas sensing. The phase of three components polycrystalline including ZnO, SnO₂ and CdS was confirmed from the XRD analysis with average crystallite space of 14.14 nm and a microstrain of 3.14 × 10^-3 reflecting high defect density and high number of active sites on surface. A uniform nanostructured morphology to increase the effective surface area was confirmed through FESEM and AFM analyses. The strength of UV-visible absorption and the low energy band gap of 2.5 eV observed optically is indicative of interfacial effects in the multilayer system. Gas sensing tests toward 75 ppm NO₂ demonstrated a maximum sensitivity of 26% at room temperature (25^oC), with fast response and recovery behavior. The enhanced performance at room temperature is attributed to crystallite size-induced depletion effects and defect-assisted charge transfer across the heterointerfaces. These results indicate that the ZnO/SnO₂/CdS/p-Si heterostructure is a promising candidate for room-temperature NO₂ detection.