Strain-engineered bright excitons and a nearly flat band in monolayer SnNBr for high-speed LED applications

With the ever-increasing volume of data, the need for systems that can handle massive datasets is becoming gradually critical. High performance visible light communication (VLC) systems offer an expedient solution, yet its widespread adoption is hindered by the limited modulation bandwidth of light emitting diodes (LEDs). Through <i>ab initio</i> many-body perturbation theory within the <i>GW</i> approximation and the Bethe-Salpeter equation (BSE) approach, this work introduces a novel approach to achieving exceptionally high modulation bandwidth by utilizing the nearly flat bands in two-dimensional semiconductors, using SnNBr monolayer as a prototype material for overcoming this bottleneck. Utilizing its unique properties of a direct bandgap and a nearly flat highest valence band, we demonstrate the achievement of exceptionally high modulation bandwidths on the order of terahertz, surpassing the capabilities of established materials such as InGaN and GaN. Interestingly, the excellent absorption and recombination features of the SnNBr monolayer can be modulated further by the application of in-plane tensile strain. The strain-induced proliferation of bright excitons in the visible region, coupled with enhanced absorption and accelerated recombination rates, provides a deeper understanding of the fundamental mechanisms at play in two-dimensional materials, laying the groundwork for future explorations in light-matter interactions at terahertz frequencies.