  Graphene provides a unique platform for hosting high quality 2D electron
systems. Encapsulating graphene with hexagonal boron nitride (hBN) to shield it
from noisy environments offers the potential to achieve ultrahigh performance
nanodevices, such as photodiodes and transistors. However, the absence of a
bandgap at the Dirac point presents challenges for using this system as a
useful transistor. In this study, we investigated the functionality of
hBN-aligned monolayer graphene as a field effect transistor (FET). By precisely
aligning the hBN and graphene, bandgaps open at the first Dirac point and at
the hole-doped induced Dirac point via an interfacial moir\'e potential. To
characterize this as a submicrometer scale FET, we fabricated a global bottom
gate to tune the density of a conducting channel and a local top gate to switch
off this channel. This demonstrated that the system could be tuned to an
optimal on/off ratio regime by separately controlling the gates. These findings
provide a valuable reference point for the further development of FETs based on
graphene heterostructures.
