Raman spectra and electron-phonon coupling in disordered graphene with gate-tunable doping

TL;DR

This study investigates how gate-tunable doping and introduced defects affect the Raman spectra and electron-phonon interactions in graphene, revealing disorder-induced reductions in coupling strength and spectral feature modifications.

Contribution

It provides new insights into the effects of controlled disorder and doping on Raman spectral features and electron-phonon coupling in graphene.

Findings

Raman G peak shows a minimum frequency and maximum width near the charge-neutral point.

Disorder weakens the dependence of Raman parameters on doping levels.

Electron-phonon coupling strength decreases with increased disorder.

Abstract

We report a Raman spectroscopy study of graphene field-effect transistors (GFET) with a controlled amount of defects introduced in graphene by exposure to electron-beam irradiation. Raman spectra are taken at T = 8 K over a range of back gate voltages (Vg) for various irradiation dosages (Re). We study effects in the Raman spectra due to Vg-induced doping and artificially created disorder at various Re. With moderate disorder (irradiation), the Raman G peak with respect to the graphene carrier density (nFE) exhibits a minimum in peak frequency and a maximum in peak width near the charge- neutral point (CNP). These trends are similar to those seen in previous works on pristine graphene and have been attributed to a reduction of electron-phonon coupling strength (D) and removal of the Kohn anomaly as the Fermi level moves away from the CNP. We also observe a maximum in I2D/IG and weak maximum in ID/IG near the CNP. All the observed dependences of Raman parameters on nFE weaken at stronger disorder (higher Re), implying that disorder causes a reduction of D as well. Our findings are valuable for understanding Raman spectra and electron-phonon physics in doped and disordered graphene.