Effect of Remote Surface Optical Phonon Scattering in Ferroelectric-Gated Single- and Bi-layer Graphene*

We investigate the effect of the remote surface optical (RSO) phonon scattering on the transport properties of single and bi-layer graphene gated by ferroelectric Ba_0.6Sr_0.4TiO₃ (BSTO) thin films. Graphene flakes were exfoliated on epitaxial 100-300 nm BSTO thin films grown on Nb-doped SrTiO₃ substrates. Single and bi-layer samples were then identified via optical microscopy and characterized by atomic force microscopy and Raman spectra. Selected flakes were fabricated into field effect transistor (FET) devices via e-beam lithography. At low temperature, these ferroelectric-gated FETs (FeFET) exhibit resistivity hysteresis induced by ferroelectric switching, which evolves to anti-hysteresis at ~40 K. The graphene FETs exhibit high field effect mobility up to µ_FE~19,000 cm²/Vs and quantum Hall at 10 K, from which we deduced a dielectric constant of ~60 for BSTO. We examined the temperature dependence of the resistivity, which reveals dominant RSO phonon scattering from the interface with BSTO. We also discuss the effect of capping these samples with a top h-BN layer. Our study facilities the development of high-performance FeFETs based on graphene.