Exciton Manipulation via Dielectric Environment Engineering in 2D Semiconductors.

Abstract

Two-dimensional (2D) semiconductors are promising for photonic applications due to their exceptional optoelectronic properties, including large exciton binding energy, strong spin-orbit coupling, and potential integration with the standard complementary silicon-oxide-semiconductor (CMOS) technology. The dielectric environment can significantly affect the photoluminescence (PL) spectra of transition metal dichalcogenide (TMD) monolayers by modulating excitonic properties such as optical transitions and binding energies. Specifically, substrates with higher dielectric permittivity reduce exciton binding energy and the quasiparticle bandgap. Doping and the charge carrier concentration can further modify the emitted spectra by affecting the PL excitonic content. Increased doping can enhance trion formation and bandgap renormalization phenomena, leading to PL spectral shifts that depend on the semiconductor type. This study systematically investigates the substrate-induced dielectric screening, doping, and trapped charges in CVD-grown n-type 1L-WS₂ and p-type 1L-WSe₂ transferred onto CMOS-relevant SiO₂ and HfO₂ dielectrics. Our results show that p-type 1L-WSe₂ exhibits higher PL intensity and red-shifted trion emission on HfO₂, whereas n-type 1L-WS₂ shows a blue-shifted, lower-intensity PL for a similar dielectric environment. The difference arises from the interplay of the semiconductor type, doping, dielectric screening, and charge carrier concentration. We demonstrate that suspending the monolayers at the nanoscale enhances PL by reducing nonradiative recombination, enabling controlled micro-PL patterning and the formation of localized emission hot spots. Our results provide valuable insights for the development of next-generation CMOS-compatible optoelectronic devices.