W doping effect on the dielectric properties of amorphous Ga2O3 films grown on Si substrate for low-k applications

Tungsten doped gallium oxide (Ga2O3:W) thin films were prepared by vacuum evaporation method on glass and silicon substrates. The W doping level was measured by the energy dispersive X-ray fluorescence (EDXRF) analysis. The molar ratio of W to Ca was 9.6%, 13.4%, 18.2%, 22.7%, and 30.4%. The crystalline state of the prepared oxide films was determined by the X-ray diffraction method. The oxide films deposited on silicon substrate have amorphous structure while those oxide films deposited on glass substrate show crystalline structure of beta-Ga2O3, which confirms that the WO3 oxide was totally doped in the lattice of Ga2O3 forming solid solution (SS). The electrical properties of the prepared amorphous W-doped films were studied for samples made in form of MOS: Au/Ga2O3:W/Si configuration. It was observed that W doping of certain level reduces the effective dielectric constant of Ga2O3:W film to less than that of SiO2, i.e. the doping with WO3 turns the high-k gallium oxide dielectric into low-k insulator. The dielectric relaxation of the doped films was studied through the complex dielectric modulus M*, from which the high-frequency dielectric constant epsilon'(infinity) the most probable relaxation time (tau) as a function of W-doping level was determined. The temperature dependent of the dc-current passes through Au/Ga2O3:W/Si arrangement predicts the red shift of the bandgap due to W doping. (C) 2012 Elsevier Ltd. All rights reserved.