Improvement of Some Physical and Sensing Properties of Nanostructured Cadmium Oxide Manganese Thin Films

Abstract

The spray pyrolysis technique (SPT) was employed for depositing thin films of Mn-doped CdO. The structural analysis through XRD confirms films polycrystallinity with a cubic phase. AFM analysis reveals adecline in particle size and surface roughness. The optical transmittance spectra indicate that the films exhibit high transparency in the visible area. The absorption edge shifting toward longer wavelengths as Mn concentration increases. The band gap reduced from 2.75 eV for CdO to 2.65 eV for 4% Mn-doped CdO. The refractive index exhibits normal and abnormal dispersion regions, decreasing with higher Mn doping. The extinction coefficient follows the trend of the absorption coefficient, increasing with photon energy, confirming direct electronic transitions in the films. CdO:Mn films show p-type behavior; NO2 exposure (250 ppm) reduces resistance. 4% Mn doping increases resistance by altering charge carrier concentration. As Mn concentration increases, the sensitivity of CdO films to NO2 decreases. Sensitivity increases with NO2 concentration due to stronger gas-film interactions and higher conductivity.