When the thickness of layered crystal MoS2 reduces from three-dimensional bulk to monolayer film, the electronic structure changes dramatically from indirect to direct band, resulting in significant photoluminescent behaviors changes. Because of the novel bandgap transition, monolayer MoS2 shines lights on field-effect transistors (FETs), phototransistors, photodetectors and photovoltaic devices applications. As for common device architecture such as transistors and photonic structure, it is rigorously required to place MoS2 on dielectric substrate to form vertical heterostructure. The elemental physical properties of monolayer MoS2 are influenced by the interaction between the thin-film and the substrate. In this study, utilizing monolayer MoS2 on LaAlO3 and SrTiO3 substrates, SiO2 and Gel-film, the group of Qi Zeming at NSRL systematically investigate the substrate effect on the property of monolayer MoS2 by Raman and photoluminescence. The Raman spectra show that the substrate has a small influence on the Raman modes of monolayer MoS2, which suggests weak strain effect between monolayer MoS2 and substrates. However, they observed significantly substrate-dependent photoluminescence of monolayer MoS2, originating from substrate-to-film charge transfer. Through the selection of desired substrate, they are able to induce different amounts of charge into the monolayer MoS2, which consequently modifies the neutral exciton and charged exciton (trion) emissions. Finally, they proposed a band-diagram model to elucidate the relation between charge transfer and the substrate Fermi level and work function. Their work demonstrates that the substrate charge transfer exerts a strong influence on the monolayer MoS2 photoluminescence property, which should be considered during device design and application. The work also provides a possible route to modify the thin-film photoluminescence property via substrate engineering for future device design. This work was published on Nanoscale, 2014, 6, 15248-15254. 

Modify the photoluminescence of monolayer MoS2 through substrate charge transfer effect