Role of dopant Ga in tuning the band gap of rutile TiO2 from first principles

The influences of different doped Ga amount on the band gaps of rutile TiO₂ have been investigated systematically using density functional theory calculations. The calculation results show that the substitutions of Ga can make the configurations more stable, and the lower doped amount can induce the red shift of the absorption edge by reducing their band gaps, such as Ga₁Ti₁₅O₃₂ and Ga₃Ti₁₃O₃₂ samples, whereas the band gaps slightly increase with the higher doping amount. The narrower band gaps are due to the valence band edges shifting upwards with energy levels of impurities produced by lower Ga doping amount, however, the wider band gaps are caused by the dominant rises of conduction band bottoms when Ga doping contents are larger. As a result, proper doping content of Ga can reduce their band gaps and improve the light absorption performances of TiO₂ gradually.