First-principles study of native defects in anatase TiO2

Native point defects in anatase TiO2 are investigated by using first-principles pseudopotential calculations based on density-functional theory (DFT). Antisite defects, namely, Ti-antisite (Ti-O) and O-antisite (O-Ti), have high formation energies and are hence unstable. In contrast, all other fundamental native defects (Ti-i, O-i, V-Ti, and V-O) have low formation energies. In particular, titanium interstitial (Ti-i) is a quadruple donor defect with lowest formation energy in p-type samples, whereas Ti vacancy (V-Ti) is a quadruple acceptor defect with lowest formation energy in n-type samples. Interstitial oxygen (O-i) would spontaneously and strongly bind to lattice oxygen, resulting in a neutral O-2 dimer substituting on one O site. None of the four low-energy defects have energy levels inside the DFT band gap.