Electronic structure and optical properties of SnO2:F from PBE0 hybrid functional calculations

Abstract

The structural, electronic band structure and optical properties of SnO2 and SnO2:F are investigated as a function of fluorine (F) concentration by first-principles calculation using PBE0 hybrid exchange–correlation functional. Various supercells were constructed and optimized corresponding to different F content. An increase in the lattice parameters is obtained with increasing F level. Two different Sn–F bond lengths behavior are observed, where one of them is more sensible to F concentration. Lowdin charge analysis, related to charge transfer of Sn(0), Sn (1), O(5) and F(5), is presented and discussed, including the contribution of empty orbits 5d and 4f from Sn atoms. SnO2:F materials display characteristics of the n-type semiconductor, occupied states contributed mostly from hybridized Sn 5s, Sn 5p, O 2s and O 2p states in the conduction band increase with an increase in F concentration. Density of states (DOS) diagram of SnO2:F shows a band gap-like behavior inside the conduction band. The F dependence of the direct band gap, optical band gap, band gap-like and Burstein–Moss shift are calculated and discussed. A high concentration of fluorine (around 16 at.%) shows a transformation from direct to an indirect band gap. The imaginary dielectric function presents intra-band transition around Fermi level corresponding to Drude´s electrons. Also, inter-band transitions from valence band to conduction band and from occupied conduction band to unoccupied conduction band are evident from the optical spectra.