Many-Body Effects\non Electronic Properties and Optical\nResponse of Single-Layer Penta-NiN<sub>2</sub> for Infrared Optoelectronics

We present a comprehensive first-principles study on\nthe optoelectronic\nproperties of the single-layer nickel diazenide (penta-NiN<sub>2</sub>), a pentagon-based 2D semiconductor with ideal Cairo tessellation,\nwhose bulk counterpart has been recently synthesized. To address its\nquasiparticle band structure and excitonic effects on its optical\nabsorption spectrum, we carry out ab initio calculations based on\nmany-body perturbation theory within the <i>GW</i>-Bethe–Salpeter\nequation (BSE) framework. Our results reveal a quasiparticle band\ngap of 1.05 eV by employing the eigenvalue self-consistent <i>GW</i> approach, corroborating its potential in optoelectronics.\nThe band gap exhibits an anomalous negative dependence on temperature,\nverified through the band gap pressure coefficient. Acoustic phonon-limited\nscattering analyses indicate an ultrahigh hole mobility of ∼87\n× 10<sup>4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> along the [010] direction. The most prominent absorption peak of\nmonolayer penta-NiN<sub>2</sub> is associated with resonant excitons,\ncorresponding to transitions from the valence band maximum to conduction\nband minimum + 2, which is explained by analyzing the state symmetry\nof the band edges. Hence, this pentagonal 2D semiconductor exhibits\ncompelling and promising properties deserving deeper exploration in\ninfrared optoelectronics and high-speed devices.