Integration of MoSe₂ Monolayers with Epitaxial High-Κ Gd₂O₃ Substrate: Implication for High-Quality Emission and Modulation of Excitonic Quasiparticles

Monolayer (ML) transition-metal dichalcogenides (TMDCs) represent a novel class of materials for investigating excitonic quasiparticles in two dimensions and designing novel nanoscale optoelectronic devices. Practical application of the TMDC MLs requires their integration with appropriate substrates. In this context, dielectric substrates are of particular interest. Here, we report on the impact of an epitaxial high-Κ dielectric substrate on the excitonic quasiparticles in TMDC MLs. Investigations were performed by comparing the photoluminescence (PL) response of exfoliated MoSe2 MLs directly transferred onto an epitaxial Gd2O3 layer grown on Si(001) and for comparison on the same Gd2O3 layer covered with a few monolayers of hexagonal boron nitride (hBN) (hBN/Gd2O3). We demonstrate that in reference to hBN, the epitaxial Gd2O3 substrate does not induce any significant biaxial strain to the MoSe2 MLs. Epitaxial Gd2O3 led to a strong reduction in the inhomogeneous broadening of the emission peaks of MoSe2 MLs and only a marginal red shift in the A exciton and X– trion peak positions in comparison to the hBN/Gd2O3 substrate. The PL response of MoSe2 MLs on epitaxial Gd2O3 is dominated by X– trion resonance over a large range of temperatures, revealing strong charge transfer doping by the substrate. Our work illustrates the effect of the epitaxial high-κ dielectric substrate on the optical properties of MoSe2 monolayers and paves the way for realizing high-quality emission and modulation of excitonic quasiparticles through substrate engineering.