First-Principles Insights into Recently Synthesized α′–B8H4 Hydrogenated Borophene: A Stable Semiconducting Monolayer for UV Photodetection and Optoelectronic Applications

While diverse previously fabricated pristine and hydrogenated borophene lattices have been characterized predominantly by their metallic nature, a recent experimental breakthrough has introduced α′–B8H4, a semiconducting hydrogenated borophene phase, opening new avenues for boron-based nanoelectronics. Spurred by this breakthrough, herein we utilize a comprehensive first-principles framework to investigate the critical properties of α′–B8H4 monolayer. Stability analyses confirm the considerable dynamical and thermal robustness of the α′–B8H4 monolayer. Calculations using hybrid functionals show that suspended single-layer α′–B8H4 exhibits an indirect semiconducting behavior, with band gaps of 2.06 eV and 2.45 eV predicted by HSE06 and PBE0, respectively. Optical response calculations reveal strong in-plane absorbance in the UV region, with the first notable peak at ~3.65 eV and the main peak occurring between 4.20 and 4.45 eV, both of which are clearly within the ultraviolet range. Mechanical analysis reveals that α′–B8H4 exhibits decent in-plane strength (>10 N/m), while phononic transport calculations yield a moderately low room-temperature lattice thermal conductivity of ~20 W/m·K, both displaying slight anisotropic behavior. These results provide a comprehensive first-principles characterization of the α′–B8H4 monolayer, highlighting the rare emergence of semiconducting behavior in borophene derivatives and underscoring its potential for UV optoelectronics and nanoscale device applications.