Functional silicene and stanene nanoribbons compared to graphene: electronic structure and transport

Since the advent of graphene, other 2D materials have garnered interest; notably the single element materials silicene, germanene, and stanene. We investigate the ballistic current–voltage (I–V) characteristics of armchair silicene and stanene armchair nanoribbons (AXNRs with X = Si, Sn) using a combination of density functional theory and non-equilibrium Green's functions. The impact of out-of-plane electric field and in-plane uniaxial strain on the ribbon geometries, electronic structure, and (I–V)s are considered and contrasted with graphene. Since silicene and stanene are sp2/sp3 buckled layers, the electronic structure can be tuned by an electric field that breaks the sublattice symmetry, an effect absent in graphene. This decreases the current by ∼50% for Sn, since it has the largest buckling. Uniaxial straining of the ballistic channel affects the AXNR electronic structure in multiple ways: it changes the bandgap and associated effective carrier mass, and creates a local buckling distortion at the lead-channel interface which induces a interface dipole. Due to the increasing sp3 hybridization character with increasing element mass, large reconstructions rectify the strained systems, an effect absent in sp2 bonded graphene. This results in a smaller strain effect on the current: a decrease of 20% for Sn at 15% tensile strain compared to a ∼75% decrease for C.