  Two-dimensional semiconducting transition metal dichalcogenides embedded in
optical microcavities in the strong exciton-photon coupling regime may lead to
promising applications in spin and valley addressable polaritonic logic gates
and circuits. One significant obstacle for their realization is the inherent
lack of scalability associated with the mechanical exfoliation commonly used
for fabrication of two-dimensional materials and their heterostructures.
Chemical vapor deposition offers an alternative scalable fabrication method for
both monolayer semiconductors and other two-dimensional materials, such as
hexagonal boron nitride. Observation of the strong light-matter coupling in
chemical vapor grown transition metal dichalcogenides has been demonstrated so
far in a handful of experiments with monolayer molybdenum disulfide and
tungsten disulfide. Here we instead demonstrate the strong exciton-photon
coupling in microcavities comprising large area transition metal dichalcogenide
/ hexagonal boron nitride heterostructures made from chemical vapor deposition
grown molybdenum diselenide and tungsten diselenide encapsulated on one or both
sides in continuous few-layer boron nitride films also grown by chemical vapor
deposition. These transition metal dichalcogenide / hexagonal boron nitride
heterostructures show high optical quality comparable with mechanically
exfoliated samples, allowing operation in the strong coupling regime in a wide
range of temperatures down to 4 Kelvin in tunable and monolithic microcavities,
and demonstrating the possibility to successfully develop large area transition
metal dichalcogenide based polariton devices.
