Correlation effects and electronic properties of Cr-substituted SZn with an intermediate band.
A study using first principles of the electronic properties of S32Zn31Cr, a material derived from the SZn host semiconductor where a Cr atom has been substituted for each of the 32 Zn atoms, is presented. This material has an intermediate band sandwiched between the valence and conduction bands of the host semiconductor, which in a formal band-theoretic picture is metallic because the Fermi energy is located within the impurity band. The potential technological application of these materials is that when they are used to absorb photons in solar cells, the efficiency increases significantly with respect to the host semiconductor. An analysis of the gaps, bandwidths, density of states, total and orbital charges, and electronic density is carried out. The main effects of the local-density approximation with a Hubbard term corrections are an increase in the bandwidth, a modification of the relative composition of the five d and p transition-metal orbitals, and a splitting of the intermediate band. The results demonstrate that the main contribution to the intermediate band is the Cr atom. For values of U greater than 6 eV, where U is the empirical Hubbard term U parameter, this band is unfolded, thus creating two bands, a full one below the Fermi energy and an empty one above it, i.e., a metal-insulator transition.
Tablero
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Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, Madrid, Spain. ctablero@etsit.upm.es