Optical, structural and electrical properties of ZnO - Co thin films prepared by sol-gel method

Abstract

ZnO thin films of 90 nm was doped with cobalt by the Sol-gel method and it was deposited by spinning on borosilicate glass (1 cm x 1cm), the effect of molar percentage (1 to 7 %) and the annealing temperature (400, to 600°C) on their electric properties and the relation with their morphology, crystal structure and optical properties have been evaluated. X-ray diffraction measurements (u.a) and the UV-VIS absorption bands intensity (u.a.) indicated that all ZnO thin films showed hexagonal wurtzite, and no secondary phases were detected. The thin films crystallinity increasing with the annealing temperature, but it's independent of % dopant; the particle size increased (11 to 26 nm) with the annealing temperature and decrease (in 5 nm) with % Cobalt; independent of direction chosed the morphology change of nanorods to nanoparticles with % Cobalt. The increase in 1% of cobalt and the temperature at 600°C decrease E in 0.12 eV and move the λexc 11 nm to greater energy, showing a poor quantum g confinement regimen. The parameters of lattice are independent of % Co and annealing temperature, the 7 % molar cobalt increase the carriers number of 10 to 10 e-/cm , while the carriers mobility decrease of 26x10 to 5x10 cm /V.s and increase in five magnitude orders in function of the annealing temperature.