Annealing-induced phase transformation in vapor deposited tellurium dioxide thin films and its structural, chemical analysis

Tellurium dioxide (TeO₂) thin films were synthesized by thermal vacuum deposition on glass substrate and samples were annealed from 250 °C to 400 °C at 50 °C interval. The annealing was found to have a significant impact on the structural, optical, and electrical properties of TeO₂ thin films. X-ray diffraction spectra (XRD) revealed an increase in crystallite size and corresponding decrease in micro strain and dislocation density with increasing temperature. Annealed sample at 350 °C and 400 °C showed phase change from γ-TeO₂ to β-TeO₂ since β phase is thermodynamically favourable with greater free energy change. X-ray Photoelectron spectroscopy of all annealed sample confirm the improvement in formation of TeO₂ from metallic Tellurium with air annealing. The XPS analysis also confirmed the existence of interstitial Oxygen, and its concentration increased at 400 °C. Raman spectroscopy employed to investigate the variation in vibrational modes with temperature and correlate these findings with other structural and chemical analyses. Photoluminescence study of TeO₂ thin films reveals evolution of defect states with annealing temperature. Decrease in intensity of defect-related emissions (green, near-IR) suggests improved crystallinity which was in turn supported by the disappearance of low-level defect peaks upon annealing.