First-principles study of Cl-terminated silicon nanoribbons electronic properties

Based on density functional pseudopotential calculations, the electronic properties of Cl- -terminated silicene nanoribbons (SiNRs) -with either zigzag edge (ZSiNRs) or armchair edge (ASiNRs)- are studied. The results show that all the Cl-terminated ZSiNRs present a zero gaps except for the 2-, 3- and 4-ZSiNRs, which have narrow band gaps. We also found degenerate flat edge-state bands at Fermi level (E_F),which give rise to a very large density of states (DOS). The Cl-terminated ASiNRs are semiconductors regardless of their widths and the band gaps exhibit oscillatory behavior allowing the classification into three distinct families as 3k, (3k + 1) and (3k + 2), where k is a positive integer. Furthermore, the band gaps are the largest for the 3k group, moderate for (3k+1) and the smallest for members of the (3k + 2). Because of the ρ—ϕ mixing effect, the total density of states (DOS) and projected density of states (PDOS) of Cl-terminated ASiNR show that the Cl atoms affect the width between the top of the valance band or the bottom of the conduction band. The charge density distributions show that there is covalent bonding between all sorts of Si-Si bonds, with ionic bonding between the edge Cl atom and the nearest Si atom. This results from the electro-negativity of Si atoms being smaller than that of Cl atoms. (paper)