Effect of Lanthanum Doping on Spray‐Deposited ZnO Thin Films for Carbon Monoxide Gas‐Sensing Applications

Carbon monoxide (CO) detection is crucial in several areas, such as environmental monitoring, industrial safety, and health care, due to its colorless, odorless, and highly toxic nature even at low concentrations. In this study, we report the effect of lanthanum (La) doping (0.2–0.8 at%) on zinc oxide (ZnO) thin films to develop a cost‐effective, efficient, and eco‐friendly room‐temperature CO gas sensor. A low‐cost spray deposition method was used to fabricate pure and La‐doped ZnO thin films to examine their optical, morphological, structural, and CO gas‐sensing characteristics. X‐ray diffraction (XRD) investigation confirmed the formation of a hexagonal wurtzite structure free of secondary phases. Surface morphology analyzed by atomic force microscopy (AFM) revealed a nonmonotonic fluctuation (11.2–44.4) in root‐mean‐square (RMS) roughness with doping concentration, reflecting changes in grain development and refinement. UV–vis spectroscopy showed that films are highly transparent (>80%) across the visible to near‐infrared region. Gas‐sensing results showed that La doping greatly improves sensing performance; 0.6 at% La‐doped film showed the highest response (142%) with fast, repeatable response/recovery behavior (24.4 s/44 s) at room temperature, whereas pure ZnO showed a modest response. These findings highlight the significance of optimal La doping concentration for effective CO gas detection.