Seminarium Advanced Methods of Semiconductor Research – 4 listopada 2025
We cordially invite you to Advanced Methods of Semiconductor Research Seminar on Tuesday 4th of November 2025 at 13:15 in room 321, building A-1, where there will be delivered a lecture:
From excitonic complexes to extremely high excitionic g-factors in TMDs alloys
by Katarzyna Olkowska-Pucko
from Institute of Experimental Physics, Faculty of Physics, University of Warsaw
The lecture abstract is attached below.
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Semiconducting transition metal dichalcogenide (S-TMD) alloys are a new class of two-dimensional (2D) layered materials that combine the structural and optical properties of conventional S-TMDs with an additional degree of freedom, compositional tunability. By varying the ratio of the constituent elements, one can precisely adjust the optical and electronic properties of S-TMD alloys, including the emission energy, making these materials highly attractive for tailored optoelectronic applications such as tunable light sources and photovoltaics [1–3].
In this seminar I will present two exemplary alloy systems: WSSe, where the chalcogen atoms are mixed, and MoWSe₂, which contains two different transition metal atoms. I will discuss how alloying in monolayers (MLs) of these materials modifies their optical properties, such as exciton emission energy and g-factors, compared to the basic TMD MLs such as WS₂, WSe₂, and MoSe₂.
By means of photoluminescence (PL) spectroscopy, the optical properties of WSSe MLs with an S/Se ratio of 57/43, deposited on a SiO₂/Si substrate and encapsulated in hexagonal boron nitride (hBN) flakes, were investigated. The WSSe MLs were assigned to the family of materials with a dark excitonic ground state. In addition to the neutral bright A exciton line, three emission features were observed and attributed to negatively charged excitons. The application of in-plane and out-of-plane magnetic fields enabled an unambiguous identification of the bright and dark (spin- and momentum-forbidden) negative trions, as well as the phonon replica of the dark spin-forbidden complex [4].
The magneto-optical properties of MoxW1-xSe2 MLs with different Mo and W concentrations, encapsulated in hBN were investigated. Low-temperature PL measurements performed in out-of-plane magnetic fields up to 30 T revealed that the excitonic g-factors in MLs of MoWSe2 gradually change from about −4 to −10 with increasing W content. First-principles calculations reproduced this tunability and indicated that it originates from alloy-induced mixing of the conduction-band states in the K and Q valleys. This hybridization explains the observed non-monotonic dependence of the neutral exciton g-factor on alloy composition [5]. Alloying in S-TMD MLs efficiently enhances excitonic g-factors to values previously observed only for interlayer excitons in S-TMD heterostructures [6], offering a simpler platform for valleytronic and quantum applications.
[1] M. Zhang et al., ACS Nano 8, 7130–7137 (2014).
[2] L. M. Xie, Nanoscale 7, 18392–18401 (2015).
[3] Y. Sun et al., J. Am. Chem. Soc. 139, 11096–11105 (2017).
[4] K. Olkowska-Pucko et al., 2D Mater. 10, 015018 (2023).
[5] K. Olkowska-Pucko et al., arXiv:2503.23071 (2025).
[6] K. L. Seyler et al., Nature 567, 66–70 (2019).