Engineering charge transfer doping of MoSe₂ monolayers via epitaxial orientation-dependent surface electron accumulation in high-κ dielectric Gd₂O₃ thin films

Precise control over the doping concentrations of 2D transition metal chalcogenide (TMDC) monolayers (MLs) effectively tunes their physical properties for desired applications. Dielectric substrate surface charge transfer doping (SCTD), which modulates carrier concentration in TMDCs by injecting or extracting carrier charges due to work-function differences, has emerged as a non-destructive and simpler alternative to conventional doping techniques. Understanding the surface properties of epitaxial high-κ dielectrics can provide an excellent platform for the SCTD engineering of TMDC MLs. In this study, we report the SCTD of MoSe₂ MLs by epitaxial Gd₂O₃(110)/Si(100) and Gd₂O₃(111)/Si(111) layers through temperature-dependent photoluminescence investigations. Comparing the photoluminescence characteristics of MoSe₂ MLs on hBN as control samples, we demonstrate a strong enhancement in trion emission for MoSe₂ MLs in contact with epitaxial Gd₂O₃ layers. Enhanced trion emission, resulting from SCTD of MoSe₂ MLs by epitaxial Gd₂O₃ layers, indicates electron doping of approximately 1.18 × 10¹⁰ cm⁻² in the case of Gd₂O₃(111)/Si(111), increasing to 3.81 × 10¹¹ cm⁻² for Gd₂O₃(110)/Si(100). Detailed experimental investigations and theoretical analysis revealed a higher surface concentration of oxygen vacancies for Gd₂O₃(110) compared to Gd₂O₃(111) layers, which effectively controls the surface electron accumulation and, thus, SCTD of the adjacent MoSe₂ MLs. These results demonstrate a unique approach to reliably tune the SCTD of 2D TMDC MLs using epitaxial dielectric substrates.