Dresden 2006 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 34: Impurities/Amorphous semiconductors
HL 34.3: Vortrag
Mittwoch, 29. März 2006, 17:45–18:00, BEY 154
Local atomic order and optical properties in amorphous and laser-crystallized phase-change materials — •Wojciech Wełnic1,2, Silvana Botti2, Matthias Wuttig1, and Lucia Reining2 — 1I. Physikalisches Institut IA, RWTH Aachen, 52056 Aachen, Germany — 2Laboratoire des Solides Irradies, École Polytechnique, Palaiseau, France
Understanding the optical contrast between the amorphous and the crystalline state is one of the scientific challenges in phase change materials. In this work we present optical spectra calculations for crystalline and amorphous GeTe a prototype phase-change alloy.
Recent experimental data reveal that covalent semiconductors like GeTe or the ternary alloy Ge1Sb2Te4 exhibit a profound change in local atomic order upon the phase transition from the crystalline to the amorphous state: Ge atoms which occupy octahedral sites in the crystalline state become tetrahedrally coordinated in the amorphous state. Based on these findings a simple structural model of amorphous GeTe was constructed to perform ab initio ground state and excited state calculations to reveal the change in optical properties.
The optical spectra are calculated in the Random Phase Approximation. The eigenvalues are corrected with the GW Approximation and two-particle excitations are taken into account within the framework of the Bethe-Salpeter-Equation. The results are in good qualitative agreement with experimental data and furthermore explain the profound change in absorption upon amorphization.