Electronic structure and optical properties of CuGaS 2 and CuInS 2 solar cell materials (original) (raw)

The ground-state and optical properties of the americium monopnictides, AmX ͑X = N, P, As, Sb, and Bi͒ are investigated theoretically on the basis of first-principles electronic structure calculations, employing the local density approximation ͑LDA͒ as well as the LDA+ U approach. The LDA predicts pseudogap-like behavior in AmN and narrow gap ͑39-78 meV͒ semiconducting behavior in AmP to AmBi at ambient conditions. The LDA+ U calculations predict semiconducting behavior with a real gap of 192 meV for AmN and a pseudogap in AmP to AmBi. The computed semiconducting or pseudogap character is in fine agreement with the first photoemission experiments performed on AmN and AmSb films by Gouder et al. ͓preceding paper, Phys. Rev. B 72, 115122 ͑2005͔͒. This property is shown to result from the strong Am spin-orbit interaction, the Coulomb repulsion, and the particular p-d-f hybridizations. The calculated equilibrium lattice constants obtained for the AmX series using the LDA+ U technique are in good agreement with available experimental data. Also, the binding energies of the 5fs computed with the LDA+ U approach correspond well to 5f binding energies deduced from the photoemission spectra measured by Gouder et al. The high, temperature-independent paramagnetic susceptibilities of the AmX are successfully explained by a Van Vleck mechanism. A pressureinduced valence transition at high pressure is predicted for AmN.