Enhanced Raman scattering and weak localization in graphene deposited on GaN nanowires

TL;DR

This study demonstrates that GaN nanowires significantly enhance Raman scattering and induce weak localization effects in graphene, revealing changes in optical, electrical properties, and defect dynamics due to nanowire interaction.

Contribution

It provides new insights into how GaN nanowires influence graphene's optical and electronic properties, including spectral shifts, defect distribution, and weak localization phenomena.

Findings

Raman scattering intensity is enhanced over 50-fold for the 2D transition.

GaN nanowires induce homogeneous strain and modulate carrier concentration in graphene.

Weak localization effects are influenced by electron interactions with charges on nanowires.

Abstract

The influence of GaN nanowires on the optical and electrical properties of graphene deposited on them was studied using Raman spectroscopy and microwave induced electron transport method. It was found that interaction with the nanowires induces spectral changes as well as large enhancement of Raman scattering intensity. Surprisingly, the smallest enhancement (about 30-fold) was observed for the defect induced D' process and the highest intensity increase (over 50-fold) was found for the 2D transition. The observed energy shifts of the G and 2D bands allowed to determine carrier concentration fluctuations induced by GaN nanowires. Comparison of Raman scattering spatial intensity maps and the images obtained using scanning electron microscope led to conclusion that vertically aligned GaN nanowires induce a homogenous strain, substantial spatial modulation of carrier concentration in graphene and unexpected homogenous distribution of defects created by interaction with nanowires. The analysis of the D and D' peak intensity ratio showed that interaction with nanowires also changes the probability of scattering on different types of defects. The Raman studies were correlated with weak localization effect measured using microwave induced contactless electron transport. Temperature dependence of weak localization signal showed electron-electron scattering as a main decoherence mechanism with additional, temperature independent scattering reducing coherence length. We attributed it to the interaction of electrons in graphene with charges present on the top of nanowires due to spontaneous and piezoelectric polarization of GaN. Thus, nanowires act as antennas and generate enhanced near field which can explain the observed large enhancement of Raman scattering intensity.