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

Abstract

Cadmium acetate Cd(CH3COO)2·2H2O and lanthanum nitrate La(NO3)3·6H2O 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(100) substrates by sol–gel method. The spin coater technique was employed and the prepared films were pre-annealed at 400°C. The films were characterised by energy dispersion X-ray 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, 0.115nm vs. 0.097nm for Cd2+. It was observed that La-doped film with 27at.% was growing on Si substrate as an almost single crystal of [111] orientation. Then, as the doping level increased to 31at.%, 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 3eV.