  Vertical stacking of atomically thin layered materials opens new
possibilities for the fabrication of heterostructures with favorable
optoelectronic properties. The combination of graphene, hexagonal boron nitride
and semiconducting transition metal dichalcogenides allows fabrication of
electroluminescence (EL) devices, compatible with a wide range of substrates.
Here, we demonstrate a full integration of an electroluminescent van der Waals
heterostructure in a monolithic optical microcavity made of two high
reflectivity dielectric distributed Bragg reflectors (DBRs). Owing to the
presence of graphene and hexagonal boron nitride protecting the WSe$_2$ during
the top mirror deposition, we fully preserve the optoelectronic behaviour of
the device. Two bright cavity modes appear in the EL spectrum featuring
Q-factors of 250 and 580 respectively: the first is attributed directly to the
monolayer area, while the second is ascribed to the portion of emission guided
outside the WSe$_2$ island. By embedding the EL device inside the microcavity
structure, a significant modification of the directionality of the emitted
light is achieved, with the peak intensity increasing by nearly two orders of
magnitude at the angle of the maximum emission compared with the same EL device
without the top DBR. Furthermore, the coupling of the WSe$_2$ EL to the cavity
mode with a dispersion allows a tuning of the peak emission wavelength
exceeding 35 nm (80 meV) by varying the angle at which the EL is observed from
the microcavity. This work provides a route for the development of compact
vertical-cavity surface-emitting devices based on van der Waals
heterostructures.
