Manipulation of trions to enhance the excitonic emission in monolayer p-MoS₂ and its hetero-bilayer by reverse charge injection

Monolayer 2D transition metal dichalcogenides (TMDs) are known for their direct bandgaps and pronounced excitonic effects, which facilitate efficient light absorption and high photoluminescence (PL). In this study, we report a significant enhancement in PL emission from monolayers of p-type molybdenum disulfide (p-MoS₂), fabricated on conductive substrates-such as indium tin oxide (ITO) and gold (Au). We attribute this behaviour to the reverse injection of charge carriers from substrates to p-MoS₂ and the subsequent localization of electrons and holes in the substrate and p-MoS₂, respectively. Such injection of charge carriers was suppressed when few-layer graphene (FLG) was used as a barrier layer. Further investigation of the PL emission characteristics from a vertically stacked hetero-bilayer (the p-n interface) of p-MoS₂ and n-MoSe₂ revealed a single resonant high-emission PL peak at 1.64 eV with the PL emission from this heterostructure significantly higher than that from free-standing monolayers. This finding contrasts sharply with the PL quenching often seen in hetero-bilayers with an n-n interface. These findings offer valuable insights into the fundamental optical and electronic properties of 2D TMDs and their heterostructures, which are essential for optimizing these materials for optoelectronic applications.