Regensburg 2002 – scientific programme

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HL: Halbleiterphysik

HL 38: Poster 2

HL 38.7: Poster

Thursday, March 14, 2002, 16:30–19:00, Poster A

Properties of cubic and hexagonal polytypes of group-IV elements in equilibrium and under pressure — •Christophe Raffy, Jürgen Furthmüller, and Friedhelm Bechstedt — Friedrich-Schiller-Universität Jena, Institut für Festkörpertheorie und Theoretische Optik, Max-Wien-Platz 1, D-07743 Jena

Some experimental evidence for hexagonal silicon has been reported in the past. For this reason, we study cubic and various hexagonal polytypes of C, Si and Ge, at the equilibrium and under hydrostatic pressure, by means of ab initio calculations. We use the DFT-LDA method in a pseudopotential-plane-wave approach. For each polytype (3C, 2H, 4H, 6H), atomic structure, total energy and enthalpy are determined for equilibrium and strained configurations. While 3C is the most stable polytype for each element, pressure-induced phase transitions to hexagonal forms are found to be possible. The results are interpreted within the ANNNI model restricted to the third nearest neighbours. Stacking fault energies are derived. Electronic properties are also studied. We discuss the influence of polytypism, pressure and chemical nature of the material on the band structure. We especially focus on the energy gaps and the position of the conduction band minima.