Abstract
Tip-enhanced Raman spectroscopy (TERS) is used to characterize nanoscale correlations between strain and nanowire dimensions in Ge-Si0.5Ge0.5 core-shell nanowires, and to elucidate phonon-carrier interactions that are manifested via shifts in Raman peaks originating from Ge-Ge vibrational modes within the quantum-confined hole gas formed at the Ge-Si0.5Ge0.5 interface. Two distinct peaks associated with Ge-Ge vibrational modes are observed – one arising from Ge-Ge vibrations in the nanowire Ge core region, and the other from Ge-Ge vibrations occurring within the quantum-confined hole gas at the Ge-Si0.5Ge0.5 interface. Both peaks exhibit a dependence of Raman shift on local nanowire diameter consistent with coherent strain in the nanowire, demonstrating that the TERS measurements provide the ability to probe strain at the nanoscale. The separation between these peaks is a consequence of coupling between intervalence band transitions and the Ge-Ge phonon mode leading to Fano resonance behavior and a shift in the phonon self-energy.
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