Stacking up Electron-Rich and Electron-Deficient Monolayers to Achieve Extraordinary Mid- to Far-Infrared Excitonic Absorption: Interlayer Excitons in the C3B/C3N Bilayer

Our ability to efficiently detect and generate far-infrared (i.e., terahertz) radiation is vital in areas span-ning from biomedical imaging to interstellar spectroscopy. Despite decades of intense research, bridging the terahertz gap between electronics and optics remains a major challenge due to the lack of robust materi-als that can efficiently operate in this frequency range, and two-dimensional (2D) type-II heterostructures may be ideal candidates to fill this gap. Herein, using highly accurate many-body perturbation theory within the GW plus Bethe-Salpeter equation approach, we predict that a type-II heterostructure consisting of an electron-rich C3N and an electron deficient C3B monolayers can give rise to extraordinary optical activities in the mid-to far-infrared range. C3N and C3B are two graphene-derived 2D materials that have attracted increasing research attention. Although both C3N and C3B monolayers are moderate-gap 2D materials, and they couple only through the rather weak van der Waals interactions, the bilayer heterostruc-ture surprisingly supports extremely bright, low-energy interlayer excitons with large binding energies of 0.2-0.4 eV, offering an ideal material with interlayer excitonic states for mid-to far-infrared applications at room temperature. We also investigate in detail the properties and formation mechanism of the inter -and intralayer excitons.

Automated summary

Using highly accurate many-body perturbation theory, we predict that a type-II heterostructure made of C3N and C3B monolayers can exhibit extraordinary optical activity in the mid-to far-infrared range. This heterostructure supports bright, low-energy interlayer excitons with large binding energies, providing an ideal material for mid-to far-infrared applications at room temperature.