Structural and optoelectrical properties of nanocrystalline Gd-doped CdO films prepared by sol gel method

Gd-doped CdO thin films with various Gd concentrations have been prepared on glass and Si wafer substrates using sol gel technique. The films were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, and dc-electrical measurements. XRF method was used to determine the %Gd content in the films while XRD was used to study the influence of Gd doping on the detailed crystalline structure. Experimental data indicate that Gd³⁺ doping with level of less than 2.4% slightly enlarge the CdO crystalline unit cell. The bandgap (E _g) of Gd-doped CdO suffers narrowing by about 13% due to a small (0.2%) doping level but with %Gd doping level larger than 2.4%, E _g becomes wider than that of undoped CdO. The electrical behaviours of the Gd-doped CdO films show that they are degenerate semiconductors. The 2% Gd-doped CdO film shows increase in its mobility by about 92%, conductivity by 320%, and carrier concentration by 127%, relative to undoped CdO film. From transparent-conducting-oxide point of view, the Gd doping of CdO by sol gel method is not effective. Finally, the absorption in the NIR spectral region was investigated to be due to the free electrons.