Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 33: II-VI Halbleiter I
HL 33.1: Vortrag
Mittwoch, 26. März 2003, 16:15–16:30, BEY/118
Lattice dynamics in (Be,Zn)Se systems from first-principles simulations — •Andrei Postnikov1, Olivier Pagès2, Teddy Tite2, Mustapha Ajjoun2, and Joseph Hugel2 — 1Universität Osnabrück – Fachbereich Physik, 49069 Osnabrück — 2Institut de Physique, 1 Bd Arago, Université de Metz, F-57078 Metz, France
Zn-Be chalcogenides are an attractive class of mixed semiconductors with highly contrasted bond stiffness. Earlier Raman analysis has shown a quite atypical bi-modal behavior in the Be-VI vibrational range at intermediate composition, that was interpreted in terms of a novel bond-percolation phenomenon. Apparently between Be-VI and Zn-VI bond percolation thresholds (0.19 to 0.81 Be content), the Zn-Be alloys can be described as composite systems in what regards their mechanical properties. Pseudo-infinite Be-VI and Zn-VI treelike chains (which coexist within the percolation regime) delimit regions with high and low stiffness coefficients, respectively. It is expected that the short Be-VI bonds would undergo a much larger tensile strain to match the surrounding lattice parameter in the “hard” regions than in the “soft” ones, with an immediate effect on the involved Be-related vibration frequencies. With the aim to test microscopically the tentatively so explained bi-modal behaviour, we perform frozen phonon calculations (after full lattice relaxation) on a sequence of representative (Zn,Be)Se supercells containing both percolating Be-Se chains and isolated Be-Se bonds. We apply an ab initio tight-binding method (SIESTA) that uses norm-conserved pseudopotentials and efficient strictly localized numerical basis functions.