Ge-Sb-Te phase change materials

Multi-component Te alloys, and in particular those lying along the GeTe-Sb2Te3 (GST) pseudo-binary line, have been granted a key role in the development of devices for optical storage and, more recently, non-volatile memories. These alloys belong to the phase-change materials (PCMs) as they exhibit large differences in optical reflectivity and electrical resistivity between the crystalline and the amorphous state, and they can be repeatedly switched back and forth between the two states optically as well as electrically.


We pioneered the growth of GST alloys by molecular beam epitaxy (MBE) and demonstrated the successful fabrication of high-quality epitaxial single-crystalline GST layers on Si(111) and the control of GST phase, composition, and ordering. The growth of such samples is challenging because single-crystalline layers can only be obtained at substrate temperatures at which desorption significantly affects the layer composition. Hence, we employ in- and ex-situ characterization tools to achieve the necessary level of control.


Recently, we concluded the project “Epitaxial phase change superlattices designed for investigation of non-thermal switching”, that was funded in the Leibniz competition. For such superlattices with periods of only few atomic layers, we demonstrated switching at dramatically reduced power compared to alloys. Also, we unveiled a behavior between fully decoupled two‐dimensional and covalently bonded three‐dimensional materials. This weak coupling opens up new opportunities for strain engineering, with implications for PCM as well as thermoelectric properties.


Currently, we are a partner in the EU project BeforeHand and actively involved in the development of high temperature and long data retention PCMs complying with the requirements of automotive applications. In this context, we investigate epitaxial Ge-rich GST alloys and heterostructures.



5 Author S. Cecchi , D. Dragoni , D. Kriegner , E. Tisbi , E. Zallo , F. Arciprete , V. Holý , M. Bernasconi , R. Calarco

Interplay between structural and thermoelectric properties in epitaxial Sb2+xTe3 alloys

Source Adv. Funct. Mater. , 29 , 1805184 ( 2018 )
DOI : 10.1002/adfm.201805184 | 3046 Cite : Bibtex RIS
S. Cecchi, D. Dragoni, D. Kriegner, E. Tisbi, E. Zallo, F. Arciprete, V. Holý, M. Bernasconi, and R. Calarco

4 Author M. Boniardi , J. E. Boschker , J. Momand , B. J. Kooi , A. Redaelli , R. Calarco

Evidence for thermal-based transition in Super-Lattice (SL) phase change memory

Source Phys. Status Solidi RRL , 13 , 1800634 ( 2019 )
DOI : | 3010 Cite : Bibtex RIS
M. Boniardi, J. E. Boschker, J. Momand, B. J. Kooi, A. Redaelli, and R. Calarco

3 Author V. Bragaglia , F. Arciprete , A. M. Mio , R. Calarco

Designing of epitaxial GeSbTe alloys by tuning phase, composition and vacancy ordering

Source J. Appl. Phys. , 123 , 215304 ( 2018 )
DOI : 10.1063/1.5024047 | Download: PDF | 3007 Cite : Bibtex RIS
V. Bragaglia, F. Arciprete, A. M. Mio, and R. Calarco

2 Author R. Wang , F. R. L. Lange , S. Cecchi , M. Hanke , M. Wuttig , R. Calarco

2D or not 2D: Strain tuning in weakly coupled heterostructures

Source Adv. Funct. Mater. , 28 , 1705901 ( 2018 )
DOI : 10.1002/adfm.201705901 | 2955 Cite : Bibtex RIS
R. Wang, F. R. L. Lange, S. Cecchi, M. Hanke, M. Wuttig, and R. Calarco

1 Author S. Cecchi , E. Zallo , J. Momand , R. N. Wang , B. J. Kooi , M. A. Verheijen , R. Calarco

Improved structural and electrical properties in native Sb2Te3/GexSb2Te3+x van der Waals superlattices due to intermixing mitigation

Source APL Mat. , 5 , 026107 ( 2017 )
DOI : 10.1063/1.4976828 | Download: PDF | 2848 Cite : Bibtex RIS
S. Cecchi, E. Zallo, J. Momand, R. N. Wang, B. J. Kooi, M. A. Verheijen, and R. Calarco


Dr. Lutz Geelhaar

Head of Department

+49 30 20377-359