Oxygen passivation as effective technique for tailoring the nature of band gap of silicon nanowires

Silicon nanowires have been subjected to several experiential and theoretical studies, including chemical tuning with different substituents aiming to tailor the band gap as well as increasing optical absorption efficiency of solar energy. In this study, we report the effect of oxidation on silicon nanowires compared to hydroxyl passivation using theoretical DFT calculations. Surprisingly, extensive oxidation dramatically decreases the silicon nanowire band gap down to 0.26 eV. Furthermore, moderate oxidation substantially decreases the band gap compared to the equivalent amount of hydroxyl-passivated silicon nanowires. The dipole moment resulting from the different possible orientations of substituents or oxygen atoms shows a minor effect on the band gap. The relation between the band gap, percentage of oxidation, and their effects on geometrical deformations are discussed in details.