Bandgap narrowing in CdO doped with europium

Lightly Eu-doped CdO thin films (0.4%, 0.5%,0.8%, and 1.1%) 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 data indicate that Eu3+ doping slightly stresses the CdO crystalline structure and changes the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 20% due to a little (0.4%) doping with Eu3+ ions. Then, as the Eu doping level was increased (for less than 1.1%), the energygap was still narrowing. This variation was explained by the bandgap shrinkage effects. The electrical behaviours of the Eu-doped CdO films show that they are degenerate semiconductors with energygap 1.5-1.8 eV. The 0.8% Eu-doped CdO film shows increase its mobility by about 3.5 times, conductivity by 40 times, and carrier concentration by 11 times, relative to undoped CdO film. From transparent-conducting-oxide point of view, Eu is sufficiently effective for CdO doping. Finally, the absorption in the NIR spectral region was studied in the framework of the classical Drude theory. (C) 2008 Elsevier B.V. All rights reserved.