2D Transition-metal dichalcogenides (TMDCs) are being widely explored for their unique opto-electronic properties. Practical applications of the TMDC monolayers (MLs) require their integration with appropriate substrate. Out of the various classes of substrates, dielectric materials are of particular interest since they can strongly influence the electron−electron or electron−hole columbic interactions in ML TMDCs, which results in the modulation of excitonic binding energies as well as band-gap renormalization. Majority of the oxides considered for investigating the influence of dielectric substrates on the optical or electrical properties of monolayer TMDCs have been either amorphous or polycrystalline. Epitaxial oxide dielectrics can offer distinct advantages, such as low surface roughness, sharp interface and the possibility of modulating interface interactions. To elucidate the influence of epitaxial high-κ oxide dielectric substrates on the excitonic properties of ML TMDCs, we have investigated the photoluminescence (PL) and reflectance response of MoSe₂ MLs on epitaxial thin films of Gd₂O₃ grown on Si. We have compared the temperature dependent PL and reflectance response of exfoliated MoSe₂ directly transferred onto epi-Gd₂O₃ with that transferred onto a few layers of hBN on epi-Gd₂O₃. We demonstrate that the use of epi-Gd₂O₃ as a substrate for MoSe₂ results in smaller exciton binding energy, a reduction in the inhomogeneous broadening of the PL peaks, an enhanced stabilization of trions, and a 6-fold increase in the trion emission intensity as compared to that on hBN.

Further we investigated the influence of dielectric thickness on the emission properties on the overlying ML MoSe₂. We demonstrate that the interference due to the dielectric thickness can modulate the line-shape and total intensity of the reflected light from the TMDCs. Our work illustrates the effect of the epitaxial high-κ dielectric substrate on the optical properties of MoSe₂ monolayers and paves way for realizing high-quality optical emission from monolayer TMDCs through substrate engineering.