Acceptor-donor codoped degenerate p-type TiO₂ semiconductor thin film for homojunction diode application

With the aim of preparing a high-quality p-type wide bandgap semiconductor, an N and F (acceptor-donor) codoped low-resistive p-type rutile TiO₂ (NF-TiO₂) thin film is deposited by pulsed laser deposition at 773 K. The combine experimental and simulation studies confirm the p-type conductivity of the NF-TiO₂ thin film, stabilized due to the substitution of double acceptor impurities with single donor impurities in the TiO₂ thin film. The structural, optical, and electrical properties of NF-TiO₂ thin film were investigated and compared to that of undoped (TiO₂) and N-doped TiO₂ (N-TiO₂) thin films. From Hall measurement, the hole concentration, mobility, and resistivity of NF-TiO₂ thin film are estimated as 2.8 × 10¹⁹ cm⁻³, 1 cm² V⁻¹ s⁻¹, and 240 mΩ-cm, respectively. The NF-TiO₂ film, featuring 60% optical transparency and low electrical resistance, exhibits degenerate semiconductor behavior with an increase in optical bandgap to 3.42 eV from 3.25 eV of TiO₂ due to the Burstein-Moss effect. The I-V curve of the NF-TiO₂/TiO₂ homojunction device exhibits Schottky (p⁺-n) diode-like interface, confirming the metallic nature of the NF-TiO₂ thin film. This work opens a new pathway for the rational design and preparation of low-resistive p-type wide bandgap semiconductor thin films for electronic and optoelectronic device applications.