Transparent conducting properties of samarium-doped CdO

Sm-doped CdO thin films (0.4, 1.1, 3, 7.5, and 9.3%) have been prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-VIS-NIR absorption spectroscopy, and dc-electrical measurements. Experimental results indicate that Sm3+ doping creates a slight compressive stress in the CdO crystalline structure and changes (and controls) the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 17% due to a light (0.4%) doping with Sm3+ ions. Then, as the Sm doping level was increased, the energygap was slightly increasing reaching a steady state (2.17 eV). This variation was explained by the available bandgap narrowing (BGN) models. The electrical behaviour of Sm-doped CdO films shows that they are degenerate semiconductors of energygaps 1.87-2.17 eV. The 0.4% Sm-doped CdO film shows increase in its mobility by about 6 times, conductivity by 36 times, and carrier concentration by 6 times, relative to undoped CdO film. From transparent-conducting-oxide point of view, Sm is sufficiently effective for CdO doping like other metallic dopants such as In, Sn, Sc, and Y.