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Owing to their phase-change properties, Ge-Sb-Te thin films, i.e., Ge{sub 2}Sb{sub 2}Te{sub 5} (GST), are being intensively studied for new concepts of non-volatile memory. The deposition technique commonly employed is sputtering, leading to poly-crystalline layers. Here it is shown that molecular beam epitaxy allows for the preparation of highly ordered Ge-Sb-Te films even on strongly lattice-mismatched substrates like Si. In situ reflection high-energy diffraction and quadrupole mass spectrometry are utilized to monitor the growth process in real time. Ex situ X-ray diffraction, atomic force microscopy and secondary electron microscopy, and X-ray fluorescence are used to investigate the structural properties, the surface morphology, and the stoichiometry of the grown films, respectively. As main result, single crystalline GST layers can be achieved on Si(111) substrates with epitaxial relationships GST[111]//Si[111] and GST//Si in the growth direction and in-plane, respectively. The growth on Si(001) instead produces (111)-oriented films with weak texture. GST thin films with a high structural order are expected to exhibit superior electrical/switching properties to the poly-crystalline layers deposited by sputtering.
Publication date: 
1 Jul 2012

Alessandro Giussani, Perumal Karthick, Peter Rodenbach, Michael Hanke, Raffaella Calarco, Henning Riechert, Wolfgang Braun

Biblio References: 
Verhandlungen der Deutschen Physikalischen Gesellschaft