Raman characterization of electronic properties of self-assembled GaN nanorods grown by plasma-assisted molecular-beam epitaxy

Abstract

We have investigated the Raman scattering of the aligned gallium nitride (GaN) nanorods grown by plasma-assisted molecular-beam epitaxy. It was determined by Raman spectroscopy that the GaN nanorods are relatively strain free. The free carrier concentration, as well as electron mobility of the GaN nanorods, was obtained by the line shape analysis of the coupled ${\mathrm{A}}_1\text{longitudinal-optical}\left(\mathrm{LO}\right)$ phonon-plasmon mode. The electron concentration and mobility of electron obtained from line shape analysis are $3.3\times {10}^{17}{\mathrm{cm}}^{-3}$ and $140{\mathrm{cm}}^2\mathrm{V}\mathrm{s}$ , respectively. The local temperature of the nanorod sample was estimated based on the ratio of Stokes to anti-Stokes Raman peak intensity. Since the position of the LO phonon peak was found to be dependent on both the temperature and the LO phonon-plasmon coupling, it is crucial to consider the temperature effect in determining the frequency of the uncoupled LO phonon mode for the line shape analysis. The frequency of the ${\mathrm{A}}_1\left(\mathrm{LO}\right)$ mode of an undoped bulk GaN was used as a reference to determine the frequency of the uncoupled ${\mathrm{A}}_1\left(\mathrm{LO}\right)$ phonon mode of the GaN nanorods.