Electronic characteristics of Metal/Insulator Super-lattice, based on the first principle electronic structure calculation

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Based on the density functional theory and the FLAPW method, the first principle electronic structure calculation has been performed for the metal Ti/Insulator MgO Superlattice.At first, atomic configuration in the superlattice interface is determined from the comparison of calculated total energies. The calculated result shows that Ti atom is in contact with the 0 atom at the interface. Based on this atomic configuration at the interface, electronic band structure of the superlattice is calculated. It is found that there are two kinds of electronic states.One is the states, which exist mainly in only the Ti or MgO layer and receive the quantum confinement effects (quasi-two dimensional electronic states). Another is the states which exist in the both Ti and MgO layers and have the finite dispersion for energy. Also there are metallic states in a Ti layer within the band gap in an insulator MgO layer and then the metallic states constitute the quasi two-dimensional electronic states in a metallic Ti layer.Based on the electronic structure and the experimental band gap in MgO, band diagram of Ti/MgO superlattices, which shows the relative position of the conduction and valence electronic states in Ti and MgO layers is obtained.Also, calculated electronic band structure is used to calculate a tunneling current, i.e., a tunneling of an electron between two metallic Ti layers through the thin MgO layer under an electric field.Xray photoelectron spectra (XPS) has been measured in the metal Ti/insulator MgO superlattice and has been discussed in relation to the valence band density of states. Two spectra before etching and after 5-minutes etching show the difference, which reflect the electronic states in MgO layer and Ti layer, being in good agreement of the theoretical density of the state. This XPS experiment is considered to show the reliability of our theoretical electronic structure calculation.