Effect of Thickness on Structural, Optical and Electrical Properties of Co-Doped ZnO Thin Films (ZnO: Cu, Al)

Co-doped ZnO thin films (CAZO) were prepared by DC magnetron sputtering. The structural, electrical and optical properties of thin films were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), optical spectrophotometer and Raderford Back Scattering (RBS) techniques. The CAZO thin films with different thicknesses had an amorphous structure. The particle distribution diagram showed that with the increase in thickness, the size of nanoparticles reached from 10 nm to 25 nm and the range of particle size changes also increased. The bandgap energy decreased with the increase in thickness, but the Urbach energy increased. The CAZO thin film with a thickness of 50 nm had lower activation energy and a higher concentration of donor carriers, but with increasing thickness, the concentration of this type of carriers (n-type) decreases, because the conduction in the layers decreases and the resistance in CAZO thin films with a thickness of 150 nm has increased.