Layer-Dependent Optical Modulation and Field-Effect-Transistor in Two-Dimensional 4H-SnS₂ Layers

Two–dimensional (2D) 4H-polytype tin disulfide (SnS₂) flakes are synthesized using the chemical vapor transport technique. The weak Van der Waals force between the 2D SnS₂ layers offers an easy exfoliation of flakes down to a bilayer of thickness ≈2.02 (±0.1) nm using a mechanical exfoliation technique. The optical and field effect transistor (FET) characteristics of the exfoliated 2D 4H-SnS₂ layers are studied. The exfoliated layers are used to fabricate the ≈13-layered SnS₂ FET. The 4H-SnS₂ exhibits a high on/off ratio of ≈10⁶ and mobility ≈1–4 cm² V⁻¹ s⁻¹. The low mobility of the 4H-SnS₂ FET devices shows an insulating state concordant with the 2D Motts variable range hopping mechanism at varying temperatures. Moreover, it is found that the optical bandgap of the 2D SnS₂ single-crystal layers is largely widened for the bilayers and tri-layers. The optical bandgap energies vary in the range of 2.56–1.99 eV. The significant alteration in bandgap energies of ≈0.57 eV offers downscaling of the 2D nanoscale semiconducting devices. Such layer-sensitive changes in optical transmittance, absorbance, and bandgap energies are reflected in Commission Internationale de L'Eclairage (CIE) chromaticity, showing the distinct color of transmittance through various 2D 4H-SnS₂ layers.