Bi₂S₃ nanosheets: A promising anisotropic two-dimensional semiconductor for polarisation-dependent optoelectronics

Birefringence, an inherent optical property of anisotropic materials, enables manipulation of light propagation properties for various photonic and optoelectronic applications including waveplates and liquid crystal displays. However, birefringence effects directly depend on the magnitude of optical path and consequently are usually negligible in atomically thin anisotropic two-dimensional materials. [1,2] In this work we show that nanometric Bi₂S₃ flakes, exhibit strong anisotropic in-plane optical properties, which provides for birefringence values as high as Dn=0.08 at wavelengths around 1050 nm. Ellipsometry, angle resolved photoemission measurements, and Density functional theory calculations allowed us to identify electronic transitions responsible of the anisotropic optical response of this material revealing, collaterally, that this material presents a notably high exciton oscillator strength. Birefringence values of Bi₂Se₃ are larger than those observed in ReSe₂ and ReS₂ nanosheets, although lower than those obtained in the less stable material Black Phosphorus. [3] These results are promising in view of the applications of Bi₂S₃ nanomaterials in photonics and optoelectronics.



[1] Xu Li, et al., Laser & Photonics Reviews 15, 2100322 (2021).

[2] Guo, Q., et al. Nat. Photon. (2024).

[3] H. Yang, et al. ACS Photonics 4, 3023–3030 (2017).