Stefano Cecchi: Interplay between Structural and Thermoelectric Properties in Epitaxial Sb2+xTe3 Alloys

Stefano Cecchi

Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany

Interplay between Structural and Thermoelectric Properties in Epitaxial Sb_2+xTe₃ Alloys

Phase change materials (PCMs) along the Sb₂Te₃-GeTe pseudo-binary line are used as the active material for non-volatile solid-state memories.¹ Impressively, it was demonstrated that PCM memory cells based on superlattices (SLs), structures made of alternating Sb₂Te₃ and GeTe layers, showed dramatically improved performance.² Moreover, strain engineering has been proposed in chalcogenide SLs to shape the switching functionality for phase change memory applications.³
I will first present our results concerning the growth and characterization of epitaxial Sb₂Te₃/GeTe SLs. Very recently we unveiled an intriguing deviation of these structures from purely two-dimensional systems.⁴ 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 Sb_2+xTe₃ films,⁵ 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 use of statistical modeling to simulate the diffraction pattern of epitaxial Ge_xSb₂Te_3+x films.

1] S. Raoux, W. Wełnic, and D. Ielmini, Chem. Rev. 110, 240 (2010).
2] R.E. Simpson, P. Fons, A.V. Kolobov, T. Fukaya, M. Krbal, T. Yagi, and J. Tominaga, Nat. Nanotechnol. 6, 501 (2011).
3] X. Zhou, J. Kalikka, X. Ji, L. Wu, Z. Song, and R.E. Simpson, Adv. Mater. 28, 3007 (2016).
4] R. Wang, F.R.L. Lange, S. Cecchi, M. Hanke, M. Wuttig, and R. Calarco, Adv. Funct. Mater. 28, 1705901 (2018).
5] S. Cecchi, D. Dragoni, D. Kriegner, E. Tisbi, E. Zallo, F. Arciprete, V. Holý, M. Bernasconi, and R. Calarco, Adv. Funct. Mater. 29, 1805184 (2019).