Cation diffusion and hybridization effects at the Mn-GaSe(0001) reacted interface: Ab initio calculations and soft x-ray electron spectroscopy studies

The electronic properties of the Mn:GaSe interface, produced by evaporating Mn at room temperature on a ε-GaSe(0001) single-crystal surface, have been studied by soft x-ray spectroscopies, and the experimental results are discussed at the light of ab initio DFT+U calculations of a model Ga1-xMnxSe (x=0.055) surface alloy. Consistently with these calculations that also predict a high magnetic moment for the Mn ions (4.73-4.83 μB), XAS measurements at the Mn L edge indicate that Mn diffuses into the lattice as a Mn2+ cation with negligible crystal-field effects. Ab initio calculations also show that the most energetically favorable lattice sites for Mn diffusion are those where Mn substitutes Ga cations in the Ga layers of the topmost Se-Ga-Ga-Se sandwich. Mn s and p states are found to strongly hybridize with Se and Ga p states, while weaker hybridization is predicted for Mn d states with Se s and p orbitals. Furthermore, unlike other Mn-doped semiconductors, there is strong interaction between the Ga-s and Mn-dz2 states. The effects of hybridization of Mn 3d electrons with neighboring atoms are still clearly detectable from the characteristic charge-transfer satellites observed in the photoemission spectra. The Mn 3d spectral weight in the valence band is probed by resonant photoemission spectroscopy at the Mn L edge, which also allowed an estimation of the charge transfer (Δ=2.95 eV) and Mott-Hubbard (U=6.4 eV) energies on the basis of impurity-cluster configuration-interaction model of the photoemission process. The Mott-Hubbard correlation energy U is consistent with the Ueff on-site Coulomb repulsion parameter (5.84 eV) determined for the ab initio calculations.