Alexander V. Kolobov

Phase Change and Memory


Herzen State Pedagogical University of Russia





  Alexander Kolobov received his PhD in 1984 and hid D.Sc. degree in 1991, both from A.F. Ioffe Physico-Technical Institute of the Academy of Sciences of the USSR. He started his scientific career in 1979 at the Ioffe Institute in the laboratory of Prof. B.T. Kolomiets, the father of amorphous semiconductors. At various periods of time he worked at the Ioffe Institute, Cambridge University (group of Prof. S.R. Elliott), École supérieure de physique et de chimie industrielles de la Ville de Paris (France), Katholieke Universiteit Leuven (Belgium), Université de Montpellier (France) and since 1994 till 2018 at the National Institute of Advanced Industrial Science and Technology. Since 2019 he is back to his native city of St Petersburg (Russia), where he received the position of Head of Department of Physical Electronics at Herzen State Pedagogical University of Russia, since 2021 he is Director of the Institute of Physics. Prof. A.V. Kolobov is an author/co-author of over 250 original papers and 4 monographs.


Abstract for Presentation

Functional chalcogenide semiconductors: input from DFT simulations



   Functional chalcogenide materials can be divided into several groups, viz., (i) chalcogenide glasses, (ii) phase-change materials, (iii) topological insulators, and (iv) two-dimensional (2D) semiconductors. All of them are very important technological materials. Thus, chalcogenide glasses are widely used in photonics, phase-change materials are at the heard of optical memory devices and non-volatile phase-change memory, of which 3D XPoint - Optane(™) is the latest implementation. Topological insulators are of great interest for quantum computing and 2D chalcogenides such as transition-metal dichalcogenides are among most studied modern materials. For recent reviews see [1-4] While in many cases the greatest progress has been achieved from experimental studies, ab-initio simulations have also played a very important role on the way to understanding the underlying processes. In this talk, I shall illustrate the importance of density functional theory (DFT) simulations as applied to various classes of functional chalcogenides. 1. Phase-change alloys. DFT simulations described in the talk helped identify crucial patterns of the local structure of the amorphous phase, demonstrated the significance of resonant bonding for holding the crystalline structure and for the optical contrast, revealed the role of electronic excitation in the phase-change process, disclosed the role of van der Waals gap reconfiguration and interdiffusion in the contrast formation in interfacial phase-change memories. 2.Topological insulators have been predicted based on ab-initio simulations, which in itself is a powerful demonstration of the important of computational materials science. Here, we demonstrate that Dirac cones form only on certain crystal surfaces of the prototypical topological insulator Sb2Te3, for some surfaces Dirac cones do not form. 3. 2D chalcogenides. Here, we demonstrate the use of DFT simulations for the case of monolayer MoTe2, where a semiconductor-metal transition under electronic excitation has been predicted. The reported results demonstrate the effectiveness of DFT simulations for insightful design of functional chalcogenide semiconductors for nano- and optoelectronics. This work has been partially supported by the Russian Science Foundation (grant No 22-19-00766)





[1] M. Wuttig and S. Raoux, Phase-change materials, Springer (2009) 446 p.
[2] A.V. Kolobov and J. Tominaga, Chalcogenides: metastability and phase-change phenomena, Springer (2012) 292 p.
[3] K. Tanaka and K. Shimakawa, Amorphous chalcogenide semiconductors and related materials,Springer (2021) 300 p.
[4] A.V. Kolobov and J. Tominaga, Two-dimensional transition-metal dichalcogenides, Springer (2016) 539 p.