Infrared study of carrier scattering mechanism in ion-gated graphene

We performed infrared transmission experiment on ion-gel gated graphene and measured carrier scattering rate γ as a function of carrier density n over a wide range up to n = 2 × 10 ¹³ cm ^-2 . γ exhibits a rapid decrease along with the gating followed by a persistent increase upon further carrier doping. This behavior of γ(n) demonstrates that the carrier is scattered dominantly by the two scattering mechanisms, namely, charged impurity (CI) scattering and short-range disorder (SR) scattering, with additional minor scattering from substrate phonons (SPP). We can determine the absolute strengths of all the scattering channels by fitting the γ(n) data and unveil the complete n-dependent map of the scattering mechanisms γ (n) = γ CI (n) + γ SR (n) + γ SPP (n). γ CI (n) and γ SR (n) are larger than those of SiO ₂ -gated graphene by 1.8 times, which elucidates the dual role of the ion-gel layer as a CI-scatterer and simultaneously a SR-scatterer to graphene. Additionally, we show that freezing of IG at low-T (∼200 K) does not cause any change to the carrier scattering.