Understanding Ti intermediate-band formation in partially inverse thiospinel MgIn2S4 through many-body approaches

Indium atoms in octahedral sites are substituted by Ti atoms in spinel MgIn2S4, where d states of Ti form an intermediate band. However, the complex spinel structure of the host semiconductor requires a supercell study of the intermediate-band compound. Self-consistent many-body approaches are applied to the smaller cell of this material, starting from the static Coulomb-hole and screened-exchange approximation to the GW approach and then carrying out a perturbative GW calculation. We discuss the influence of many-body effects on the formation of the intermediate band through a comparison with density functional theory (DFT) and DFT + U. We find that both the self-consistent parameter-freemany-body and DFT + U + G(0)W(0) calculations indicate that only a totally occupied intermediate band can be formed by Ti in inverse MgIn2S4. This justifies the use of DFT + U + G(0)W(0) to treat the supercells, when the self-consistent GW is not affordable.