Photoemission Study of the Thermoelectric Group IV-VI van der Waals Crystals with “Pudding Mold” Band Structure
Agata Tołłoczko a, Szymon Zelewski a, Michał Błaszczak a, Natalia Olszowska b, Marcin Rosmus b, Sefaattin Tongay c, Robert Kudrawiec a
a Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, Wrocław 50-370, Poland
b Solaris National Synchrotron Radiation Centre, Jagiellonian University, Czerwone Maki 98, 30-392 Kraków, Poland
c School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287-6106, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
#2DSUSY - 2D Nanomaterials for Sustainable Energy
València, Spain, 2023 March 6th - 10th
Organizers: Maria Antonia Herrero Chamorro and Maurizio Prato
Poster, Agata Tołłoczko, 367
Publication date: 22nd December 2022

Semiconducting group IV-VI van der Waals crystals (MX, where M = Ge, Sn, and X = S, Se) are receiving increasing attention as two-dimensional thermoelectric materials, desired for their ability to convert waste heat into electricity [1]. Among them, SnSe is considered the most promising as it exhibits a remarkably high thermoelectric figure of merit (ZT), initially attributed to its low lattice thermal conductivity [2]. However, it has been shown that the electronic band structure plays an equally important role in thermoelectric performance. A certain band shape, described as a “Pudding Mold” and characteristic for all MXs, has been predicted to significantly improve ZT by combining good electrical conductivity with high Seebeck coefficient [3,4]. In this study, we explore this subtle feature experimentally for GeS, SnS, and SnSe by means of angle-resolved photoemission spectroscopy. The results reported here greatly contribute to general understanding of the valence band dispersion of MXs, and allowed us to determine the effective mass and Fermi level position of as-grown undoped crystals. Our findings are supported by ab initio calculations of the electronic band structure.

This work was supported by the National Science Centre (NCN) Poland OPUS 15 no. 2018/29/B/ST7/02135. ARPES and XPS spectra were measured in SOLARIS National Synchrotron Radiation Centre in Krakow, Poland, under the proposal no. 202043. Computational studies were supported by WCSS and PLGrid Infrastructure.

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