Effect of Aluminium Doping on Structural and Optoelectronic Properties of Sol-Gel Derived Nanocrystalline ZnO Thin Film

Highly transparent sol gel derived conducting Al-doped nanocrystalline ZnO (AZO) thin films have been prepared on glass substrates by spin coating technique. The effect of Al doping on the structural, optical and electrical properties of these films were investigated. X-ray diffraction patterns confirm that undoped ZnO and AZO films were polycrystalline with hexagonal wurtzite structure. Both XRD and SEM results show that there is a decrease of the grain size with increasing Al concentration in ZnO. Atomic force micrographs indicate much smaller surface roughness of the film showing significantly smooth surfaces. The optical energy bandgap was found to vary from 3.28 to 3.54 eV by changing the Al content from 0 to 3%. This shift is partly due to Burstein-Moss shift and partly due to compressive strain induced in film due to Al doping. The minimum resistivity of 5.79 x 10(-4) Omega cm was obtained for the film doped with 2 wt% Al. The study suggests that Al-doped ZnO is a promising material for using as electrode in photovoltaic solar cells and flat panel displays.