Issue 42, 2023

Optical properties of orthorhombic germanium sulfide: unveiling the anisotropic nature of Wannier excitons

Abstract

To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in anisotropic materials. Here, we investigate the optical properties of anisotropic excitons in GeS encapsulated by h-BN using different approaches that combine polarization- and temperature-dependent photoluminescence (PL) measurements, ab initio calculations, and effective mass approximation (EMA). Using the Bethe–Salpeter Equation (BSE) method, we found that the optical absorption spectra in GeS are significantly affected by the Coulomb interaction included in the BSE method, which shows the importance of excitonic effects besides it exhibits a significant dependence on the direction of polarization, revealing the anisotropic nature of bulk GeS. By combining ab initio calculations and EMA methods, we investigated the quasi-hydrogenic exciton states and oscillator strength (OS) of GeS along the zigzag and armchair axes. We found that the anisotropy induces lifting of the degeneracy and mixing of the excitonic states in GeS, which results in highly non-hydrogenic features. A very good agreement with the experiment is observed.

Graphical abstract: Optical properties of orthorhombic germanium sulfide: unveiling the anisotropic nature of Wannier excitons

Supplementary files

Article information

Article type
Paper
Submitted
30 Jūn. 2023
Accepted
02 Sept. 2023
First published
16 Okt. 2023
This article is Open Access
Creative Commons BY license

Nanoscale, 2023,15, 17014-17028

Optical properties of orthorhombic germanium sulfide: unveiling the anisotropic nature of Wannier excitons

M. Arfaoui, N. Zawadzka, S. Ayari, Z. Chen, K. Watanabe, T. Taniguchi, A. Babiński, M. Koperski, S. Jaziri and M. R. Molas, Nanoscale, 2023, 15, 17014 DOI: 10.1039/D3NR03168C

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