Enhanced CO2 sensing properties of Fe/Al-doped SnO2 thin films: A comprehensive study of structural, optical, and electrical characteristics

This study investigates the effects of iron (Fe) and aluminum (Al) doping on tin oxide (SnO₂) thin films for carbon dioxide (CO₂) gas sensing applications. Thin films of pure SnO₂ and SnO₂ doped with varying concentrations (3–10 wt%) of Fe and Al were prepared using a sol-gel dip-coating method. The structural, optical, and electrical properties of the films were characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic force microscope (AFM), UV-Vis spectroscopy, and Hall Effect measurements. The results reveal that doping significantly alters the crystalline structure, surface morphology, optical bandgap (increasing to 4.14 eV with 10 wt% Al and decreasing to 3.21 eV with 10 wt% Fe), and electrical conductivity of SnO₂. Fe doping generally led to larger pore sizes and higher conductivity, while Al doping resulted in smaller, more uniform pores and a transition to p-type conductivity at higher concentrations. CO₂ sensing tests demonstrated enhanced sensitivity and response times for both dopants, with 10 wt% Fe-doped SnO₂ showing the highest sensitivity. Notably, 10 wt% Fe:SnO₂ exhibited the highest CO₂ sensitivity of about 1.05, while 10 wt% Al:SnO₂ showed the fastest response time of 20 s (sensitivity 0.7). Such a comprehensive analysis provides insights into the mechanisms of CO₂ detection and the potential for tailoring SnO₂-based sensors through strategic doping for improved performance in environmental monitoring and industrial applications.The work is novel and takes a systematic approach to analyze how these two dopants affect the structural, optical, electrical, and gas sensing properties of SnO₂ across a range of doping concentrations (3–10 wt%). This study introduces a comparative analysis of dual-doping with Fe and Al, which has not been systematically explored in the context of CO₂ sensing using SnO₂ thin films. The observed synergy between the dopants, especially the trade-off between sensitivity and response time, offers a new perspective for optimizing gas sensor design.