High-temperature Brown-Zak oscillations in graphene/hBN moiré field effect transistor fabricated using molecular beam epitaxy

Abstract

Graphene placed on hexagonal boron nitride (hBN) has received significant interest due to its excellent electrical performance and physics phenomena, such as superlattice Dirac points. Direct molecular beam epitaxy growth of graphene on hBN offers an alternative fabrication route for hBN/graphene devices. Here, we investigate the electronic transport of moiré field effect transistors (FETs) in which the conducting channel is monolayer graphene grown on hexagonal boron nitride by high temperature molecular beam epitaxy (HT-MBE). Alignment between hBN and HT-MBE graphene crystal lattices gives rise to a moiré-fringed hexagonal superlattice pattern. Its electronic band structure takes the form of a “Hofstadter butterfly”. When a strong magnetic field B is applied perpendicular to the graphene layer, the electrical conductance displays magneto-oscillations, periodic in B−1, over a wide range of gate voltages and temperatures up to 350 K. We attribute this behaviour to the quantisation of electronic charge and magnetic flux within each unit cell of the superlattice, which gives rise to so-called Brown-Zak oscillations, previously reported only in high-mobility exfoliated graphene. Thus, this HT-MBE graphene/hBN heterostructure provides a platform for observation of room temperature quantum effects and device applications. Moiré field-effect transistors based on graphene/hexagonal boron nitride heterostructures are promising for their high room-temperature carrier mobilities and magnetotransport properties. Here, high-temperature molecular beam epitaxy growth of graphene/hBN gives rise to a moiré-fringed hexagonal superlattice with Hofstadter butterfly electronic band structure and quantum magneto-oscillations above room temperature.