Metallic-semiconducting transition of silicon nanowires by surface passivation

Abstract

Surface passivation is one of the best techniques to eliminate the adverse effects of the dangling bonds present in the simple nanostructures and modify their electronic property. In this work, the metallic-to-semiconducting transition of silicon nanowires (SiNWs) by surface passivation has been investigated via sp 3 tight-binding calculation. The results show that without surface passivation the SiNW reveals metallic behavior with either a zero or very small negligible negative band gap since it is due to the fact that the conduction band minimum (CBM) and the valence band maximum (VBM) overlaps at the Fermi level or the CBM cross the Fermi level and located below the VBM. The results further show that when the entire surface dangling bonds are passivated with hydrogen (H) atoms the electronic property of a SiNW has been transformed from metallic to semiconducting with either a direct or indirect band gap depending upon the diameter and the orientation. This observed superior semiconducting property (excellent band gap with direct and indirect nature) with the use of H passivation of surfaces is the clear advantage of an H-passivated SiNW over non-surface passivated SiNW. It is further noted that the <110>-oriented H-passivated SiNW exhibits direct band gap semiconductor behavior due to the reason that the CBM and the VBM are located at the same Γ point within their band structures while all <100>-oriented, <111>-oriented, and <112>-oriented H-passivated SiNWs exhibit indirect band gap semiconductor behavior due to the reason that the CBM located at X point and the VBM located at Γ point within their band structures. Further, the increase band gap of each oriented H-passivated SiNW with decreasing diameter provides clear confirmation of the quantum confinement effect never happens for the case of a non-surface passivated SiNW. This is another good advantage of an H-passivated SiNW over non-surface passivated SiNW. Finally, it has been observed from these results that the H-passivated SiNWs are best suitable channel materials for designing high performance novel transistors due to their tunable band gap and due to their direct band gap for <110> orientation they are suitable optically active material for photonic applications.