Excitonic spectral features of 1L-WSe2 with silicon nitride waveguide coupling

In this study, we present excitonic spectral features of 1L-WSe2 coupled to a platform with Silicon nitride (SiNx) waveguides, allowing us to excite and collect signals in different polarizations. In our high quality BN/1L-WSe2/BN/SiNx sample, bright neutral exciton, intervalley/intravalley trions, dark exciton, and bi-exciton and exciton-trion states can be clearly resolved, in agreement with previous reports. The dark exciton, which is known to have out-of-plane dipole moment and thus has been elusive in most standard optical measurements, can be selectively enhanced with out-of-plane light waveguide coupling scheme. Moreover, we study the resonance excitation with 1s bright and dark excitons with different polarizations. Interestingly, as we resonantly excite at dark exciton with out-of-plane light, we observe the up-conversion of bright exciton as well as a down conversion feature lying around 25-27meV lower which indicates dark associate states as being reported to be either dark trions or phonon replica of dark exciton in WSe2.