An Efficient Strategy for Controlled Band Gap Engineering of KTaO3

In this theoretical study, a systematic investigation has been carried out to explore the effect of several anionic dopants (individually as well as in combination) on the electronic structure of KTaO3. According to the defect formation energy calculation, the formation of a codoped system is more favored in comparison to the monodoped KTaO3. All the electronic structure calculations have been performed using the Heyd, Scuseria, and Ernzerhof hybrid functional, which reproduces the band gap of KTaO3 (3.61 eV) in very close agreement with the experimental value of 3.60 eV. Although doping with N reduces the effective band gap of KTaO3, introduction of localized acceptor states may adversely affect the photoconversion efficiency. However, the band gap remains almost unchanged due to doping with F and decreases by only a small extent for Cl, Br, and I doping. The scenario, however, changes on codoping with N and any of the halogen elements, which results in the formation of charge-compensated systems. In all the cases, a clear band structure is produced, ensuring good photoconversion efficiency. The present study reveals that the extent of band gap narrowing in the case of codoping with N and F is quite significant (almost 1 eV) to improve the visible light activity of KTaO3 effectively. More interestingly, this does not involve any considerable shifting of the conduction band minimum (CBM) in the downward direction. This is very crucial for KTaO3 because its CBM potential is quite close to the hydrogen reduction potential. The CBM level is found to be shifted in the upward direction for codoping with (N, Cl/Br/I). Therefore, all the codoped systems are suitable for overall water splitting, which has also been confirmed though band edge alignment with respect to water redox levels. Thus, the present study through electronic structure calculation finds suitable dopant pairs for the controlled band gap engineering of KTaO3.