  Bilayer graphene field-effect transistors (BLG-FETs), unlike conventional
semiconductors, are greatly sensitive to potential fluctuations due to the
charged impurities in high-k gate stacks since the potential difference between
two layers induced by the external perpendicular electrical filed is the
physical origin behind the band gap opening. The assembly of BLG with layered
h-BN insulators into van der Waals heterostructure has been widely recognized
to achieve the superior electrical transport properties. However, the carrier
response properties at the h-BN/BLG heterointerface, which control the device
performance, have not yet been revealed due to the inevitably large parasitic
capacitance. In this study, the significant reduction of potential fluctuations
to ~1 meV is achieved in all-2-dimensional heterostructure BLG-FET on a quartz
substrate, which results in the suppression of the off-current to the
measurement limit at a small band gap of ~90 meV at 20 K. By capacitance
measurement, we demonstrate that the electron trap/detrap response at such
heterointerface is suppressed to undetectable level in the measurement
frequency range. The electrically inert van der Waals heterointerface paves the
way for the realization of future BLG electronics applications.
