Effect of thickness and post deposition annealing temperature on the structural and optical properties of thermally evaporated molybdenum oxide films

In this paper, the influence of thickness and post deposition annealing temperature on thermally evaporated molybdenum oxide films has been studied. The X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are used for crystal structural and surface morphological characterization of the films, respectively. The XRD analysis showed that the presence of alpha-MoO3 and MoO2 crystalline phase of the films annealed at elevated temperature similar to 250 degrees C after deposition. The optical constants are determined from UV-Vis transmission spectra. The optical band gap and Urbach energy is found to be temperature dependent. The refractive index of the films is estimated by the optical method as well as cross-sectional SEM image analysis. It is found that the refractive index of the films increases from similar to 1.70 to 2.03 with the decrease in film thickness from similar to 2.9 to 1.7 mu m. It is also observed that the refractive index decreased from similar to 2.03 to 1.61 with the increase in post deposition annealing temperature from room temperature (RT) to similar to 250 degrees C. Moreover, extinction coefficient, optical conductivity, porosity, and film density are investigated as a function of source-substrate distance and post deposition annealing temperature. The Photoluminescence (PL) properties of the films are also investigated by recording spectra under the excitation wavelength at 250 nm.