Sputtering pressure influenced structural, electrical and optical properties of RF magnetron sputtered MoO₃ films

MoO₃ films were deposited by RF magnetron sputtering technique on glass and silicon substrates held at 473 K by sputtering of metallic molybdenum target at an oxygen partial pressure of 4 × 10⁻² Pa and at different sputtering pressures in the range of 2 Pa to 6 Pa. The influence of sputtering pressure on the structure and surface morphology, electrical and optical properties of the MoO₃ thin films was studied. X-ray diffraction studies suggest that the films deposited at a sputtering pressure of 2 Pa were polycrystalline in nature with mixed phase of α- and β-phase MoO₃, while those formed at sputtering pressure of 4 Pa and above were of α-phase MoO₃. Scanning electron micrographs showed a decrement in the size of the particles and their shapes changed from needle like structure to dense films with the increase of sputtering pressure. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic vibration modes of Mo=O, Mo–O and Mo–O–Mo related to MoO₃. Electrical resistivity of the MoO₃ films decreased from 6.0 × 10⁴ Ω cm to 2 × 10⁴ Ω cm with an increase of sputtering pressure from 2 Pa to 6 Pa, respectively. Optical band gap of the films decreased from 3.12 eV to 2.86 eV with the increase of sputtering pressure from 2 Pa to 6 Pa, respectively.