Excitonic effects and optical properties of CrO₂monolayer in 2H phases

The development and proposal of new 2D materials have been expanding the frontiers for new technologies in the field of photovoltaics and optoelectronics with ultra-thin materials, especially 2D semiconductor materials. As known in the literature, the CrO₂in 2H phase presents semiconductor characteristics, but the excitonic effects and optical properties have not yet been systematically investigated. In this sense, a significant gap in the understanding of its potential for optoelectronic applications needs to be overcome. Here, we performed a systematic investigation of its structural, electronic, excitonic, and optical properties. We identified it as dynamically stable, and quasi-harmonic phonon calculations indicate that the 2H phase is thermodynamically stabilized only for temperatures 660 K within our free-energy analysis. Also, it was determined to be an indirect band gap semiconductor (0.93 eV), with a direct band gap of 1.84 eV located in K/K' valleys. Excitonic effects play an important role in the description of the linear optical response, with an exciton binding energy of 386 meV. Furthermore, these quasi-particle effects give rise to an indirect excitonic ground state, resulting in an optical band gap of 1.20 eV, which is significantly smaller than the direct electronic band gap. Consequently, high reflectivity is observed in the UV region with potential applications as a UV filter.