21 febbraio 2020

Van der Waals epitaxy and characterization of quasi-two-dimensional Ge-Sb-Te alloys and superlattices

Seminario di Dottorato in Scienza e Nanotecnologia dei Materiali

Venerdì 21 Febbraio 2020
Ore 14.00
Sala Seminari, Piano I, Edificio U5 – via Roberto Cozzi 55, Milano

Relatore: Stefano Cecchi  – Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany

Titolo: Van der Waals epitaxy and characterization of quasi- two-dimensional Ge-Sb-Te alloys and superlattices

Abstract. Phase change materials (PCMs) along the Sb2Te3GeTe pseudo-binary line are used as the active material for non-volatile solid-state memories. Impressively, it was demonstrated that PCM memory cells based on superlattices (SLs), structures made of alternating Sb2Te3 and GeTe layers, showed dramatically improved performance. Moreover, strain engineering has been proposed in chalcogenide SLs to shape the switching functionality for phase change memory applications. I will first present our results on the growth and characterization of epitaxial Sb2Te3GeTe SLs. Recently we unveiled an intriguing deviation of these structures from purely two-dimensional systems. Strikingly, an unparalleled distribution of lattice parameters, which is tunable, develops in the heterostructures. Also, it allows to realize strain engineering in such weakly coupled systems. In the second part of the talk I will present the study of the structural and thermoelectric properties of epitaxial Sb2+xTe3 films, as these represent an intriguing option to expand the concept of strain engineering in chalcogenide SLs. A combination of X-ray diffraction and Raman spectroscopy, together with dedicated simulations, allowed unveiling the structural characteristics of the alloys. The strong link existing between structural and thermoelectric properties will be shown. As an outlook, I will show preliminary results concerning the development of Ge-rich GeSbTe alloys for automotive application, in the framework of the EU project BeforeHand.