Narrow terahertz plasmon resonance of quasi-freestanding bilayer epitaxial graphene

Graphene's ability to support and manipulate THz surface plasmon polaritons make it an ideal material for tunable THz detectors operating at room temperature [1]. Currently, however, THz plasmonic resonances in epitaxially grown graphene result in broad line widths (γ) >100 cm −1 at the plasmon resonance frequency [2]. This is attributed to the partially covalent bonding between the silicon carbide (SiC) substrate and the 6√3 buffer layer between the substrate and epitaxial graphene (EG), inducing electron-phonon coupling and Coulomb scattering resulting in low carrier mobility (500–1200 cm 2 V −1 s −1 ). The buffer layer can be decoupled from the SiC by hydrogen intercalation where the passivation of Si dangling bonds promotes an additional EG layer to become quasi-freestanding bilayer epitaxial graphene (QBLEG) as shown in Fig. 1a [3]. We found that by removing this substrate induced scattering, sheet carrier density changed to p-type (∼10 13 cm −2 ) and high carrier mobility (3300–4000 cm 2 V −1 s −1 ) was observed across nominally bilayer graphene as shown by Raman in Fig. 1b. In this work we investigate if high mobility EG will result in narrowing the plasmon resonances in the THz regime as reported by theory [2].