Defect-Mediated Optical and Electrical Behaviour in γ- and β-Phase TeO2 Thin Films
摘要
Among the various crystalline phases of TeO2, the β-TeO2 phase exhibits superior carrier mobility and a wide bandgap. This study investigates the influence of defects such as oxygen interstitials and oxygen vacancies on the optical and electrical properties of thermal vapor-deposited TeO2 thin films at various annealing temperatures and its correlation with defect formation. Annealing at 350°C and 400°C improved the crystallinity, accompanied by a reduction in the optical bandgap from 2.18 eV to 1.56 eV in the γ-TeO2 phase and from 2.87 eV to 2.82 eV in the β-TeO2 phase. Photoluminescence (PL) analysis indicated that near-band-edge emissions arose from excitonic transitions (~350 nm and ~395 nm), while the concentration of oxygen interstitials remained unchanged during the annealing process. Electron paramagnetic resonance (EPR) spectroscopy was performed to determine the paramagnetic nature of the sample and to obtain the g-value, which confirmed the presence of hole-type defects, attributed to oxygen interstitials. Upon annealing up to 300°C, the charge density increased significantly from 1.9 × 1015 cm−3 to 87.5 × 1015 cm−3, while the resistivity decreased from 86.0 Ω·cm to 22.0 Ω·cm. Electrical characterization demonstrated that films annealed at 350°C and 400°C showed higher carrier mobility, aligning with the expected behaviour of the β-TeO2 phase.