A comparative investigation into the impact of Cd and Mg on the optoelectronic properties of ZnO thin films by spray pyrolysis for waveguide applications

Abstract

This study examines the impact of Mg and Cd on ZnO waveguide properties using CdxZn1−xO and CdxZn1−xO thin films (x=0, 0.03, 0.05). X-ray diffraction confirms successful Mg incorporation in the ZnO wurtzite, while CdO segregates, increasing lattice parameters. UV–Vis measurements show opposing trends in band gap energy, increasing for Mg doping and decreasing for Cd doping. Photoluminescence data reveals varying defect characteristics consistent with band gap energy behavior. Through SEM, Mg increased grain size and slightly decreased the surface density. Cd-doped films exhibit no significant morphology change by AFM measurements. Hall measurements show both Cd and Mg doping increase resistivity tenfold. Cd causes a 94.5% decrease in mobility, whereas Mg leads to a substantial 2190 times increase. Charge carrier density decreases by 105 in Mg0.05Zn0.95O and increases threefold in Cd0.05Zn0.95O. M-lines measurements demonstrate birefringent behavior, positive for Mg doping and negative for Cd doping, and a decreasing refractive index.