Authors: B.K. Agrawal, A. Pathak, S. Agrawal
Affilation: Allahabad University, India
Pages: 114 - 117
Keywords: optical absorption of nanowires, semiconducting nanowires, photonic nanowires, nanowire structures
We study the physical properties of the unpassivated and H-passivated GaN nanowires (NWs) by employing the first–principles pseudopotential method within density functional theory (DFT). Two types of the NW’s having hexagonal and triangular cross-sections have been investigated. All the NW’s after relaxation (to achieve minimum energies) show distorted structures where the chains of the Ga- and N- atoms are curved in different directions. The binding energy (BE) increases with the diameter of the NW because of decrease in the relative number of the unsaturated surface bonds. The BE’s of the triangle cross-sectional nanowires are somewhat smaller than those of the hexagon cross-sectional nanowires in accordance with the Wulff’s rule. As expected, the band gap varies appreciably with the diameter of the NW, at first falls rapidly in the small diameter nanowires and very slowly thereafter in the large diameter nanowires. These distortions are reduced with the diameters of the nanowires. The optical absorption in the GaN NW’s is quite strong in the ultra-violet (UV) region but an appreciable absorption is also present in the visible region. The present results indicate the possibility of engineering the properties of nanowires by manipulating their diameter and surface structure. Strong optical absorption around 3.0 eV has been seen for the large diameter uncompensated and H-passivated wire which is in concurrence with the peak observed at 3.25 eV by Kuykendall et al in their photoluminescence emission spectra of the large diameter GaN NW’s. The presently predicted GaN nanowires possessing the triangular cross-sections should be observable in the experiments.