Structural, electrical, and optical absorption properties of LaxCd1-xO solid solution films obtained by sol-gel method

Cadmium acetate Cd(CH3COO)(2)center dot 2H(2)O and lanthanum nitrate La(NO3)(3)center dot 6H(2)O were used to prepare the sol in the present investigation. A series of heavy La-doped CdO thin films have been prepared on amorphous glass and single-crystal Si(1 0 0) substrates by sol-gel method. The spin coater technique was employed and the prepared films were pre-annealed at 400 degrees C. The films were characterised by energy dispersion Xray fluorescence (EDXRF), X-ray diffraction (XRD), UV-vis-NIR absorption spectroscopy, and dc-electrical measurements. The EDXRF spectrum was used to determine the at.% of La doped into CdO lattice. The structural study by XRD indicates that La3+ doping grows the CdO lattice parameter due to its relatively larger standard ionic radius, 0.115 nm vs. 0.097 nm for Cd2+. It was observed that La-doped film with 27 at.% was growing on Si substrate as an almost single crystal of [1 1 1] orientation. Then, as the doping level increased to 31 at.%, La2O3 nanograins were formed together with La-doped CdO grains. This was explained according to Hume-Rothery (HR) rules and the concept of electronegativity. The electrical measurements indicates that resistivity of crystalline samples grows very strongly with increasing at.% of La doped into CdO structure. The optical absorption studies show that La3+ in large concentration increases the absorption coefficient in the visible region and widens the bandgap, from 2.42 to more than 3 eV. (C) 2008 Elsevier B.V. All rights reserved.