Micro-Raman investigations of InN-GaN core-shell nanowires on Si (111) substrate

Abstract

The electron-phonon interactions in InN-GaN core-shell nanowires grown by plasma assisted- molecular beam epitaxy (MBE) on Si (111) substrate have been analysed using micro-Raman spectroscopic technique with the excitation wavelength of 633, 488 and 325 nm. The Raman scattering at 633 nm reveals the characteristic E2 (high) and A1 (LO) phonon mode of InN core at 490 and 590 cm−1 respectively and E2 (high) phonon mode of GaN shell at 573 cm−1. The free carrier concentration of InN core is found to be low in the order ∼ 1016 cm−3 due to the screening of charge carriers by thin GaN shell. Diameter of InN core evaluated using the spatial correlation model is consistent with the transmission electron microscopic measurement of ∼15 nm. The phonon-life time of core-shell nanowire structure is estimated to be ∼0.4 ps. The micro-Raman mapping and its corresponding localised spectra for 325 nm excitation exhibit intense E2 (high) phonon mode of GaN shell at 573 cm−1 as the decrease of laser interaction length and the signal intensity is quenched at the voids due to high spacing of NWs.