Influence of substrate bias voltage on structural and optical properties of RF reactive magnetron sputtered WO3 thin films

Abstract

In this investigation, tungsten oxide (WO3) thin films have been deposited on unheated glass substrates by RF magnetron sputtering of tungsten target at constant oxygen partial pressure of 6×10−2 Pa, sputtering power of 150 W and at different substrate bias voltages in the range from 0 to -150 V. The structural and optical properties of the films were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy and UV-Vis-NIR spectrophotometers. The films formed up to substrate bias voltage of -50 V were found to be amorphous in nature, while those films formed at -100 V showed a weak (200) reflection indicates the presence of monoclinic phase of WO3 in amorphous matrix. The optical transmittance of the films was in the range 78 – 95 % in the wavelength range of 500 – 1200 nm. The absorption band edge was shifted towards higher wavelength side with increasing substrate bias voltage. The optical band gap of the films decrease from 2.81 to 2.69 eV with increase of substrate bias voltage from 0 to -150 V respectively. The refractive index of the films increased from 2.19 to 2.27 with increase of substrate bias voltage from 0 to -150 V respectively.