Band gap engineering in Zn(1−x)CdxO and Zn(1−x)MgxO thin films by RF sputtering

Band gap tuning of ZnO by Cd and Mg doping has been investigated. Cd and Mg doped ZnO thin films of different concentrations (0, 3, 10 & 20 mol%) were grown on Si(100) substrates by R.F. magnetron sputtering. The corresponding targets were prepared by the conventional solid-state reaction route. The grown films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Hall effect measurement, photoluminescence (PL), UV–vis–NIR spectroscopy and energy dispersive spectroscopy (EDS). XRD studies showed that all films are preferentially oriented along (002) plane. AFM studies showed that decrease of grain size with the increase of doping concentration. Electrical studies indicate that the resistivity of the films increased by the increase of Cd and Mg concentration. UV–vis–NIR studies showed that the optical band gap of ZnO (3.35 eV) was reduced to 2.74 eV upon Cd alloying while increased to 3.94 eV upon Mg alloying. Red and blue shift in near band edge (NBE) emission observed from PL studies for Cd and Mg alloying respectively, well acknowledged this modulation of band gaps. From modified Vegardʹs law, the bowing parameter has been estimated to be 1.9 eV and 2.59 eV for Cd and Mg alloyed ZnO films, respectively. The incorporation of dopants (Cd and Mg) in the films has been confirmed by EDS analysis.