Structural, Electronic and Optical Properties of Cr-doped SrTiO3 using Density Functional Theory

SrTiO3 is a promising photocatalyst to be used to generate solar fuels from water and CO2. However, it is only active in UV light irradiation with the wide band gap close to 3.2 eV. Doping with certain element should enhance the SrTiO3 to the visible light that also can improve the electronic and optical properties of the semiconductor. First-principles calculations based on density functional theory (DFT) are performed to investigate the effects of Cr doping on the structural, electronic, and optical properties of SrTiO3 perovskite using the local density approximation (LDA) methods with the Hubbard corrections Ud in Ti 3d states and Up in O 2p states. The best agreement of the U values to improve the electronic band gap of was found by LDA. By combining the two correction terms Ud and Up, the band gap of SrTiO3 could be enhanced, which is close to the experimental band gap. The incorporation of Cr at the Ti site significantly affects the electronic band structure of SrTiO3 by introducing new states at the G point, converting the indirect band gap into a direct one. The band structure and DOS analysis show that the Cr-doping introduces some Cr 3d gap states near the bottom of the CB hence achieving higher efficiency recombination centres of photogenerated electrons. The shift of the density of states to lower energies and enhanced interaction between the Cr atom and its neighbouring atoms after Cr doping in SrTiO3 are observed. Moreover, the partial density of states of SrTiO3 changes significantly at the lower end of the conduction band. Thus, Cr doping affects the electronic band structure of SrTiO3. Cr-doped SrTiO3 offers improved optical properties and its conversion to a direct bandgap makes it an attractive candidate for optoelectronic devices.