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Raman scattering of phonon-plasmon coupled modes in self-assembled GaN nanowires

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7 Author(s)
Jeganathan, K. ; Institute of Bio-and Nanosystems (IBN-1) and Center of Nanoelectronic Systems for Information Technology (CNI), Research Centre Jülich GmbH, D-52425 Jülich, Germany ; Debnath, R.K. ; Meijers, R. ; Stoica, T.
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We report the determination of free-electron concentration and mobility of free-standing GaN nanowires (NWs) by line shape analysis of the coupled longitudinal optical phonon-plasmon Raman modes (L+). The E2high phonon mode at 566.9 cm-1 with a sharp linewidth of 2.8 cm-1 indicates strain free NWs with high crystalline perfection. The lattice temperature of the NWs was varied between 313 and 472 K by varying the excitation laser beam power. For unintentionally doped samples at room temperature, an average electron concentration and mobility of strain free NWs were found to be ∼2×1017 cm-3 and 460 cm2/Vs, respectively. We have shown that the electron concentration does not change significantly over a temperature range between 313 and 472 K. The electron mobility decreases at high temperatures, in agreement with literature data for compact layers. For Si-doped NWs, the L+ phonon peak is strongly upshifted indicating a higher free-carrier concentration of about 1×1018 cm-3. Asymmetric broadening observed at the lower frequency side of the L+ phonon peak might be ascribed to the enhancement in surface optical modes due to the high surface-to-volume ratio of NWs.

Published in:

Journal of Applied Physics  (Volume:105 ,  Issue: 12 )