Optical properties tuning by sodium and magnesium co-doping in ZnO thin films for optoelectronic applications

Abstract

Sodium (Na) and magnesium (Mg) co-doped ZnO thin films (Na: Mg: ZnO) for a fixed 8 mol% Na concentration along with varied 1, 2 and 3 mol% Mg concentrations have been deposited on conducting fluorine-doped tin oxide (FTO) coated glass substrates using the sol-gel spin coating method. The synthesized films were annealed at 500 °C for 1 h. The structural and optical properties of annealed thin films were studied using an x-ray diffractometer and UV–visible spectrometer, respectively. Structural degradation followed by a linear red shift of the optical band gap was observed due to an increase in Mg concentration. Reflectance was decreased for higher Mg concentrations making the thin films suitable for solar cell window material. The refractive index was improved for higher Mg concentrations. Refractive index variation with Mg co-dopant concentration makes these films a suitable candidate for integrated optics. Urbach tail width increased upon increasing Mg concentrations which indicate overall increment of disorder at higher Mg concentrations.