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

Abstract

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 MoSe 2 MLs directly transferred onto an epitaxial Gd 2 O 3 layer grown on Si(001) and for comparison on the same Gd 2 O 3 layer covered with a few monolayers of hexagonal boron nitride (hBN) (hBN/Gd 2 O 3 ). We demonstrate that in reference to hBN, the epitaxial Gd 2 O 3 substrate does not induce any significant biaxial strain to the MoSe 2 MLs. Epitaxial Gd 2 O 3 led to a strong reduction in the inhomogeneous broadening of the emission peaks of MoSe 2 MLs and only a marginal red shift in the A exciton and X − trion peak positions in comparison to the hBN/Gd 2 O 3 substrate. The PL response of MoSe 2 MLs on epitaxial Gd 2 O 3 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 MoSe 2 monolayers and paves the way for realizing high-quality emission and modulation of excitonic quasiparticles through substrate engineering.

Interference-Modulated Excitonic Reflectance of Monolayer MoSe2 on Epitaxial Gd2O3 Thin Films

“…All the reflectance spectra exhibit features corresponding to the A and B excitons, which are denoted as X A and X B , respectively. Additional peaks were observed in the case of samples S-6 and S-9 below 750 nm, which is close to the emission wavelength reported for trion (charged exciton) for MLs with high electron density. , Earlier, we had reported enhanced charge-transfer electron doping into the MoSe 2 MLs by epitaxial Gd 2 O 3 layers, which is related to the surface electronic defects formed by the uncoordinated oxygen on the film’s surface . However, a detailed understanding of the dielectric layer thickness dependence of the low energy peaks remains a matter of further investigations, which is beyond the scope of the present study.…”

“…41,42 Earlier, we had reported enhanced charge-transfer electron doping into the MoSe 2 MLs by epitaxial Gd 2 O 3 layers, which is related to the surface electronic defects formed by the uncoordinated oxygen on the film's surface. 25 However, a detailed understanding of the dielectric layer thickness dependence of the low energy peaks remains a matter of further investigations, which is beyond the scope of the present study. In the present study, the impact of epitaxial Gd 2 O 3 layer thickness on the excitonic reflectance of MoSe 2 MLs has been analyzed by considering the A and B excitonic features only.…”

“…30 Our previous report demonstrated modulation of PL characteristics of MoSe 2 MLs by epitaxial Gd 2 O 3 thin films. 25 In this study, we report on the reflectance properties of MoSe 2 MLs dry-transferred onto epitaxial Gd 2 O 3 (111)/ Si(111) thin films having different thicknesses (∼6 to 50 nm). Gd 2 O 3 , which is a REO, has been reported as a promising candidate for a high refractive index material in dielectric optical multilayers with high transmittance from the ultraviolet to the infrared regime.…”

“…Among diverse dielectric materials, high-κ (κ: dielectric constant) metal-oxide dielectrics have been widely investigated for tuning the photoluminescence (PL) and electrical transport properties of various TMDC MLs. − Dielectric materials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies, which can aid to the fabrication of TMDC-based superior resonant reflectors. , Among various metal oxide dielectrics, rare earth oxides (REOs) with high refractive indices (1.75–1.95) represent a class of multifunctional materials with significant potential for their applications in photonic and optoelectronic devices . Our previous report demonstrated modulation of PL characteristics of MoSe 2 MLs by epitaxial Gd 2 O 3 thin films …”

Dielectrics for Two-Dimensional Transition-Metal Dichalcogenide Applications

“…So far, hBN is the most successful candidate for these considerations, but remains limited to unscalable exfoliated flakes. Besides hBN, other dielectrics such as MoO 3 , Ga 2 O 3 , Gd 2 O 3 , and talc (Mg 3 Si 4 O 10 (OH) 2 ) have shown initial potential as dielectrics for exciton device applications, but further experimental investigations are needed. We highlight that there are different requirements for exciton recombination based on the application.…”