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 & AP;2.02 (& PLUSMN;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 & AP;13-layered SnS2 FET. The 4H-SnS2 exhibits a high on/off ratio of & AP;10(6) and mobility & AP;1-4 cm(2) 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 & AP;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.