Suppressing remote optical phonon scattering in graphene below room temperature with touch-printed oxide Ga₂O₃

We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga₂O₃ synthesized on the surface of liquid Ga metal. Temperature-dependent electrical measurements of millimetre-scale passivated and bare CVD graphene on SiO₂/Si indicate that the passivated graphene maintains its high field effect mobility, desirable for applications. Electrical transport is often substrate-limited in graphene, resulting from the scattering of graphene electrons by charged impurities and remote optical phonons in the substrate. Surprisingly, the temperature-dependent resistivity is reduced in our passivated graphene over a range of temperatures below 230 K, due to the interplay of screening of the remote optical phonon modes of the SiO2 by the high-dielectric-constant of Ga₂O₃, and the relatively high characteristic phonon frequencies of Ga₂O₃. Raman spectroscopy and electrical measurements indicate that Ga₂O₃ passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al₂O₃.