Thermal dissociation of inter-layer excitons in MoS/MoSe hetero-bilayers.

We describe photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy of hetero-bilayers comprising monolayers (1L) of MoS and MoSe at cryogenic temperatures. A PL peak showing a decay time of 2.5 ns was observed below 100 K, which can be attributed to an inter-layer exciton emission in the 1L-MoS/1L-MoSe hetero-bilayers. An inter-layer exciton binding energy of ∼90 meV is determined from its thermal dissociation behavior; the band offset of each layer obtained from this value is consistent with previously reported first-principles calculations. Moreover, generation of inter-layer charged excitons (trions) is implied from the gate modulation of the inter-layer exciton PL spectra.