Effects of edge hydrogenation and applied electric field on the structure and electrical properties of zigzag silicene nanoribbons by SCC-DFTB calculations

The effects of edge hydrogenation and applied electric field in different directions on the geometrical structure and electrical properties of zigzag silicene nanoribbons (ZSiNRs) with different period widths (width = 2,3,4) were investigated by using a self-consistent charge density functional tight-binding (SCC-DFTB) method. The results show that the degree of warpage of the ZSiNRs is significantly changed by hydrogenation, while the bond length and bond angle are less affected. The edge hydrogenation reduces the Si-dangling bonds in the nanoribbons, which increased the binding energy of nanoribbon and enhanced system stability. In the absence of an electric field, the unhydrogenated nanoribbons with different period widths all exhibit semiconducting properties, and the hydrogenated nanoribbons exhibit metallic or semi-metallic properties. Under the vertical external electric field in the z-direction, the stability and energy gap of the unhydrogenated nanoribbons are sensitive to the change of strength, and the oscillation fluctuation is large. With the increase of strength, the atoms in the outermost four layers of the nanoribbons show obvious charge gain and loss. When the vertical electric field is applied to the hydrogenated nanoribbons, the energy gap changes are related to the period width. Their electrical properties realized the conversion between the semi-metal properties and the direct band gap semiconductor properties. Charge transfer occurs between the adjacent two layers of atoms. Under the same electric field strength, the amount of charge transfer increases from left to right along the direction of the width of the nanoribbon; at the same time, with the increase of the electric field strength, the amount of charge transfer also presents an increasing trend.