Berlin 2012 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 37: Poster II: Focused electron beam induced processing for the fabrication of nanostructures (focused session, jointly with O); Nanoengineered thin films; Layer properties: electrical, optical, and mechanical properties; Thin film characterization: structure analysis and composition (XRD, TEM, XPS, SIMS, RBS,..); Application of thin films

DS 37.29: Poster

Donnerstag, 29. März 2012, 15:00–17:00, Poster E

The ferroelectric transition in the phase-change material GeTe — •Franziska Schlich, Peter Zalden, and Matthias Wuttig — 1. Physikalisches Institut IA, RWTH Aachen University, 52074 Aachen, Germany

Phase-change materials can be cycled between the amorphous and the crystalline phase. This transition is accompanied by a significant change of the electrical resistance. The materials on the pseudo binary line between GeTe and Sb₂Te₃ are particularly suitable for memory devices. The meta-stable crystalline phase of Ge₂Sb₂Te₅ has a cubic symmetry and is characterised by atomic displacements and configurational disorder which leads to a localization of charge carriers and semiconducting properties. Also GeTe in its low temperature α-phase is claimed to have pronounced local distortions. Nevertheless in the literature two scenarios have been presented which can explain the transition to the cubic α-phase. One is based on a displacive transformation (Chattopadhyay et al.; J. Phys. C 20, p.1431, 1987) while the second one (Fons et al.; Phys. Rev. B 82, p.1431, 2010) utilizes an order-disorder phase transition.

Therefore we have investigated the phase transition of GeTe whose transition temperature is reported to depend critically on the stoichiometry. We have sputter deposited thin films of approx. 300 nm thickness and obtained Ge₅₃Te₄₇. X-ray diffraction (XRD) patterns which include information about the thermal and static disorder of the crystal lattice, have been recorded during heating. From these data we obtain important insight on the nature of the phase transition.