  Despite a rich choice of two-dimensional materials, which exists these days,
heterostructures, both vertical (van der Waals) and in-plane, offer an
unprecedented control over the properties and functionalities of the resulted
structures. Thus, planar heterostructures allow p-n junctions between different
two-dimensional semiconductors and graphene nanoribbons with well-defined
edges; and vertical heterostructures resulted in the observation of
superconductivity in purely carbon-based systems and realisation of vertical
tunnelling transistors. Here we demonstrate simultaneous use of in-plane and
van der Waals heterostructures to build vertical single electron tunnelling
transistors. We grow graphene quantum dots inside the matrix of hexagonal boron
nitride, which allows a dramatic reduction of the number of localised states
along the perimeter of the quantum dots. The use of hexagonal boron nitride
tunnel barriers as contacts to the graphene quantum dots make our transistors
reproducible and not dependent on the localised states, opening even larger
flexibility when designing future devices.
