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 Ga 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 β-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 ε∞′ and the most probable relaxation time (τ) 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.

► The dielectric constant of 9–28 at.% W-doped film was less than that of SiO2. ► The relaxation of Ga2O3–WO3 were studied through the complex dielectric modulus M*. ► The ε∞′ and the relaxation time (τ) as a function of W-doping level was determined. ► The temperature dependent predicts bandgap shrinkage with W doping by 0.2–0.4 eV.