Electronic property modulation of zigzag single-walled silicon nanotubes by carbon doping concentration

The unique properties of silicon nanotubes endow them with broad application prospects in many fields, including biosensors, solar cells and optoelectronic devices. In this paper, the effects of the carbon doping concentration on the geometrical and electronic properties of two sizes of zigzag single-walled silicon nanotubes (ZSiNTs), denoted as ZSiNT (5,0) and ZSiNT (6,0), were investigated by the self-consistent charge density functional tight-binding (SCC-DFTB) method. The increment of the carbon doping concentration can generally improve the structural stability of all the nanotubes, which arises from the increase in the proportion of the short Si-Si bond and the binding energy. Certain patterns of carbon doping have been found to regulate the band gap with a significantly larger band gap opening range for ZSiNT (5,0) compared to ZSiNT (6,0). Energy band structures indicate that carbon-doped ZSiNTs exhibit three conductive types: direct band gap semiconductor, indirect band gap semiconductor, and semi-metals. In addition, the concentration of carbon doping significantly affects the amount of charge transfer, and the charge moves to the position of carbon atom doping.