Energetics of native defects in anatase TiO₂: a hybrid density functional study

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Titanium dioxide (TiO2) is a crucial material in various applications.
• Understanding native defects is key to controlling TiO2's electronic properties.
• Intrinsic conductivity of TiO2 is predominantly n-type, but the underlying defect physics requires detailed investigation.

Purpose of the Study:

• To comprehensively investigate the energetics and electronic structures of native defects in anatase TiO2.
• To determine the role of oxygen vacancies (V_O), titanium interstitials (Ti_i), and titanium vacancies (V_Ti) in defect formation and conductivity.
• To elucidate the conditions under which n-type or p-type conductivity can be achieved in TiO2.

Main Methods:

• Utilized hybrid density functional calculations to model native defects in anatase TiO2.
• Analyzed defect formation energies and electronic structures.
• Calculated carrier densities and Fermi level positions under varying oxygen chemical potentials.

Main Results:

• Oxygen vacancies (V_O) and titanium interstitials (Ti_i) act as shallow donors, enabling carrier densities from 10¹¹ to 10¹⁹ cm^-3.
• Titanium vacancies (V_Ti) function as deep acceptors but cannot compensate for the dominant n-type conductivity.
• The Fermi level remains above the valence band maximum (2.34 eV) even under extreme conditions, precluding intrinsic p-type conductivity.

Conclusions:

• Intrinsic conductivity of TiO2 is fundamentally n-type due to the prevalence of shallow donor defects.
• Achieving p-type TiO2 necessitates external doping strategies.
• Calculated carrier concentration at typical conditions is approximately 5 × 10¹³ cm^-3.