Optical and structural insights into Ta2O5/n-Si heterojunctions: detailed characterization and material properties

A detailed investigation into the physical and optical properties of Ta₂O₅ thin films is essential for evaluating their potential in semiconductor applications. In this study, Ta₂O₅ films were deposited via RF magnetron sputtering and thermally annealed at temperatures of as-deposited, 250,500,750 and 1000 °C. Structural, optical, and electrical characterizations were performed using XRD, FTIR, AFM, UV–Vis spectroscopy, and C–V/G–V measurements. XRD results showed that crystallinity improved, defect density decreased, and grain size increased with rising annealing temperature. FTIR confirmed the formation of a SiO₂ interfacial layer around 1100 cm⁻¹, which significantly reduced interface defects and leakage currents. AFM images revealed smoother surfaces and larger grains, particularly in the 1000 °C annealed films. UV–Vis analysis using the Kubelka–Munk function demonstrated increased reflectance and a slight widening of the optical band gap from 4.07 eV to 4.13 eV, indicating sensitivity to grain size, crystal quality, and lattice strain. The C–V characteristics of as-deposited samples lacked distinct accumulation or inversion regions due to poor interface quality and high trap density. With increasing annealing temperature, C–V curves improved, corresponding to enhanced crystallinity and reduced defect states. Band-to-band transitions became dominant, and the barrier height (Φ_B) slightly decreased due to reduced interface states and improved charge transport. The effective charge density (Q_eff) and interface state density (D_it) decreased significantly with annealing, from 10¹² to 10¹¹ cm⁻² and from 10¹⁴ to 10¹⁰ eV⁻¹ cm⁻², respectively. These findings confirm that thermal treatment plays a crucial role in optimizing the structural and electronic properties of Ta₂O₅ thin films for advanced electronic devices.