Thickness-dependent electronic and optical properties of faceted hexagonal aluminum nitride nanotubes

Electronic and optical properties of aluminum nitride nanotubes are studied in the framework of density-functional theory. It is found that the surface atoms attribute their electronic states near the upper valence band edge as well as the lower conduction band edge as defect states. Moreover, the absorption spectrum of a AlN nanotube is shown to be correlated with the ratios of the surface atoms to the bulk atoms. As tube thickness increases, a AlN tube is observed to have an increased tendency to show an optical absorption of bulk wurtzite AlN. Therefore, we predict that for realistic AlN nanotubes with large thicknesses (30–80 nm), the absorption spectra are most probably originating from the electronic states arising from the bulk portion.