Band gap and THz optical adsorption of SnSe and SnSe2 nanosheets on graphene: Negative dielectric constant of SnSe

Density functional theory (DFT) calculations have been used to investigate physical–chemical sensing of various proposed interfaces as SnSe@Graphene, SnSe2@Graphene, Graphene@SnSe@Graphene, and Graphene@SnSe2@Graphene, where dispersion corrections have been included to taken into account the vdW interactions between the layers. Initially, we predicted the electronic structures, mobility and carrier concentrations (cc) of SnSe and SnSe2 structures. Using different methodology, the outcomes have confirmed the semiconductor properties of SnSe and SnSe2 with indirect bandgap of 1.20 eV and 0.94 eV calculated by Generalized Gradient Approximation (GGA) and MetaGGA (MGGA) adopted with Perdew-Burke-Ernzerhof (PBE) functional, while hybrid Heyd-Scuseria-Ernzerhof (HSE) hybrid functional overestimated the experimental observations for both materials. Room temperature high mobility and cc have predicted by 126 × 103 cm2V−1 s−1 with cc of 1.3 × 1013 cm3 for a two layers SnSe and 69 × 103 cm2V−1 s−1 with cc of 4.2 × 1018 cm3 for three layers SnSe2. Optical absorption spectrum revealed that the presence of two peaks at 60 THz and 48 THz with the intensity of 89879 cm−1 and 34504 cm−1 for interfaces including two layers of graphene. More interestingly, dielectric constant calculations showed that the transfer of carriers between graphene layers and SnSe in Graphene@SnSe@Graphene interface with absorption peak shifted to 24 THz along the in-plane direction and negative dielectric constants in the range of 24–169 THz, showing the effect of light-trapping through plasmonic.