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HL: Halbleiterphysik

HL 50: Poster II

HL 50.29: Poster

Donnerstag, 30. März 2006, 16:30–19:00, P3

The origin of high vacancy concentrations in chalcogenide alloys — •Daniel Lüsebrink, Wojciech Welnic, Christoph Steimer, and Matthias Wuttig — I. Insitute of Physics (IA), RWTH Aachen University, 52056 Aachen, Germany

Phase change materials that are used in rewritable CD’s and DVD’s show a remarkable combination of properties. They exhibit pronounced property contrast, i.e. a remarkable difference in optical properties and electronic conductivity between the amorphous and the crystalline state. This has been attributed to a considerable difference in atomic arrangement in both states. The crystalline state that is found in phase change media is a distorted rocksalt structure which is characterized by a high vacancy concentration. For example GeSb2Te4 shows a vacancy concentration of 25% at the A-site of the distorted rocksalt structure. This raises the question how structures with such high vacancy concentrations can be stabilized. To answer this question density functional theory has been employed. Calculations have been performed for both the stable crystalline state, a hexagonal atomic arrangement, as well as for metastable rocksalt structures. A reason for the surprisingly high vacancy concentration in the metastable rocksalt structure will be presented. Finally we will discuss the significance of our findings for the properties of phase change materials.