Influence of sputtering power on the physical properties of magnetron sputtered molybdenum oxide films

Thin films of molybdenum oxide were formed on glass and silicon substrates by sputtering of molybdenum target under various sputtering powers in the range 2.3–6.8 W/cm2, at a constant oxygen partial pressure of 2 × 10−4 mbar and substrate temperature 523 K employing DC magnetron sputtering technique. The effect of sputtering power on the core level binding energies, chemical binding configurations, crystallographic structure, surface morphology and electrical and optical properties was systematically studied. X-ray photoelectron spectroscopic studies revealed that the films formed at sputtering powers less than 5.7 W/cm2 were mixed oxidation states of Mo5+ and Mo6+. The films formed at 5.7 W/cm2 contained the oxidation state Mo6+ of MoO3. Fourier transform infrared spectra contained the characteristic optical vibrations. The presence of a sharp absorption band at 1,000 cm−1 in the case of the films formed at 5.7 W/cm2 was also conformed the existence of α-phase MoO3. X-ray diffraction studies also confirmed that the films formed at sputtering powers less than 5.7 W/cm2 showed the mixed phase of α-and β-phase of MoO3 where as at sputtering power of 5.7 W/cm2 showed single phase α-MoO3. The electrical conductivity of the films increased from 8 × 10−6 to 1.2 × 10−4 Ω−1 cm−1, the optical band gap decreased from 3.28 to 3.12 eV and the refractive index decreased from 2.12 to 1.94 with the increase of sputtering power from 2.3 to 6.8 W/cm2, respectively.