  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.
