Characterization of molybdenum oxide films prepared by bias magnetron sputtering

Thin films of molybdenum oxide were deposited on unheated glass substrates using dc magnetron sputtering method by sputtering of molybdenum target in the presence of oxygen and argon gas mixture under various substrate bias voltages in the range 0 to - 150 V. The effect of substrate bias voltage on the structure, electrical and optical properties was studied. From X - ray photoelectron spectroscopy studies revealed that the films formed on the unbiased substrates were substoichiometric with the presence of mixed oxidation states of Mo 6+ and Mo 5+ . As substrate bias voltage increased to -120 V, the films were stoichiometric with oxidation state of Mo 6+ . X-ray diffraction studies indicated that the films deposited on the unbiased substrates were amorphous in nature. The films formed at - 120 V were orthorhombic a - phase of MoO 3 . The films deposited under unbiased condition showed high electrical conductivity of 3.6x10 4 Ω -1 cm -1 due to the amorphous nature, while those films deposited at the substrate bias voltage of -120 V showed the decrease in the electrical conductivity to 4.5x10 -5 Ω -1 cm -1 due to the partial filling of oxygen vacancies. The unbiased films showed an optical band gap of 3.03 eV with the refractive index of 2.03. As the substrate bias voltage increased to -120 V the optical band gap of the films increased to 3.22 eV and refractive index increased to 2.13 due to the improvement in the crystallinity and packing density of the grown films.