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HL: Halbleiterphysik

HL 24: Poster II

HL 24.93: Poster

Mittwoch, 25. März 1998, 10:30–19:00, A

Electronic structure of FeS₂ : The crucial role of electron-lattice interaction — •V. Eyert¹, K.-H. Höck², S. Fiechter¹, and H. Tributsch¹ — ¹Hahn-Meitner-Institut, Glienicker Straße 100, D-14109 Berlin, Germany — ²Institut für Physik, Universität Augsburg, Memminger Straße 6, D-86135 Augsburg, Germany

We present the results of fully self-consistent all electron first-principles calculations for semiconducting iron pyrite. The ASW calculations are based on density functional theory within the local density approximation. The electronic properties are dominated by strongly hybridized Fe 3d and S 3p states. Chemical stability as analyzed by an ab initio implementation of the crystal orbital overlap population (COOP) is shown to result mainly from the Fe-S bonding. While the upper part of the valence band is formed mainly from Fe 3d t_2g derived states the conduction band comprises the e_g derived levels. The conduction band minimum in contrast is exclusively due to S 3p states this fact explaining the observed high optical absorption. For the same reason the optical properties are strongly influenced by the short sulfur-sulfur bonds. We demonstrate that only small deviations in the sulfur pair bond lengths involve rather drastic changes of the near-gap electronic states which might even turn the indirect bandgap into a direct one. These findings allow to understand the rather high sensitivity of the optical bandgap to the incorporation of defects. Finally, our results open new perspectives for photovoltaics applications of FeS₂ .