Title: Surface optical modes in GaN nanowires

Authors: Prasana Sahoo, S. Dhara, S. Dash, A.K. Tyagi, Baldev Raj, C.R. Das, P. Chandramohan, M.P. Srinivasan

Addresses: Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Materials Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. ' Water and Steam Chemistry Laboratory, Bhabha Atomic Research Centre Facilities, Kalpakkam 603 102, India. ' Water and Steam Chemistry Laboratory, Bhabha Atomic Research Centre Facilities, Kalpakkam 603 102, India

Abstract: We investigate the optical phonons in crystalline GaN nanowires using Raman spectroscopy. Reduced phonon lifetime in the nanostructures is attributed to the increased anisotropy in lattice vibrations. Apart from the group theoretically allowed optical phonons, new phonon modes around 652 cm⁻¹ and 691 cm⁻¹ have been observed. In view of its good agreement with values in GaN, the observed phonon mode is assigned as surface optical (SO) phonon. This could be attributed to the surface modulation along the GaN nanowire diameter and it is quantitatively evaluated with observed surface morphology and the calculated dispersion relation corresponding to SO phonon modes. The modulation in the surface morphology, observed in the present study, is typical of the vapour-liquid-solid growth process. The instability in the surface phonon potential activates the SO phonon modes, which is well explained in this present study.

Keywords: surface optical modes; surface modulation; Raman spectroscopy; gallium nitride; nanowires; nanotechnology; anisotropy; lattice vibrations; surface morphology; optical phonons; surface phonons.

DOI: 10.1504/IJNT.2010.034690

International Journal of Nanotechnology, 2010 Vol.7 No.9/10/11/12, pp.823 - 832

Published online: 17 Aug 2010 *

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