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 degrees C to 400 degrees C at 50 degrees 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 degrees C and 400 degrees C showed phase change from gamma- TeO 2 to (3- TeO 2 since (3 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 degrees 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.