Growth and Characterization of n-Type Hexagonal Ta₂O₅:W Films on Sapphire Substrates by MOCVD

Tantalum oxide is a wide bandgap material commonly used as an insulating dielectric layer for devices. In this work, hexagonal Ta₂O₅ (δ-Ta₂O₅) films doped with tungsten (W) were deposited on α-Al₂O₃ (0001) by metal-organic chemical vapor deposition (MOCVD). The effects of W doping on the structural, morphology, and photoelectrical properties of the obtained films were studied. The results showed that all W-doped films were n-type semiconductors. The XRD measurement result exhibited that the increase in the W doping concentration leads to the changes in the preferred growth crystal plane of the films from δ-Ta₂O₅ (101¯1) to (0001). The 1.5% W-doped film possessed the best crystal quality and conductivity. The Hall measurement showed that the minimum resistivity of the film was 2.68 × 10⁴ Ω∙cm, and the maximum carrier concentration was 7.39 × 10¹⁴ cm³. With the increase in the W concentration, the surface roughness of the film increases, while the optical bandgap decreases. The optical band gap of the 1.5% W-doped film was 3.92 eV. The W doping mechanisms were discussed.