Impact of Fe doping on the electronic structure of SrTiO₃ thin films determined by resonant photoemission

Epitaxial thin films of Fe doped SrTiO₃ have been studied by the use of resonant photoemission. This technique allowed us to identify contributions of the Fe and Ti originating electronic states to the valence band. Two valence states of iron Fe²⁺ and Fe³⁺, detected on the base of x-ray absorption studies spectra, appeared to form quite different contributions to the valence band of SrTiO₃. The electronic states within the in-gap region can be attributed to Fe and Ti ions. The Fe²⁺ originating states which can be connected to the presence of oxygen vacancies form a broad band reaching binding energies of about 0.5 eV below the conduction band, while Fe³⁺ states form in the gap a sharp feature localized just above the top of the valence band. These structures were also confirmed by calculations performed with the use of the FP-LAPW/APW+lo method including Coulomb correlations within the d shell. It has been shown that Fe doping induced Ti originating states in the energy gap which can be related to the hybridization of Ti and Fe 3d orbitals.