A first-principles study on electronic structure, optical and thermal properties of BeX (X = C, N and O) monolayers

Abstract

The electrical, thermal, and optical characteristics of hexagonal BeX (where X = C, N and O) monolayers are studied using density functional theory. The electronegativity ratio across the Be-X bond determines whether the BeX monolayers take on metallic properties or keep functioning as semiconductors. BeC and BeN monolayers with large electronegativity differences exhibit metallic characteristics, whereas BeO with small electronegativity differences exhibits semiconductor-like properties. The phonon band structures of all three considered compounds indicate their dynamical stability as there is no negative frequencies. Accordingly, a semiconductor monolayer shows an active optical response in the vacuum-UV, whereas a metallic monolayer displays an optical response in the IR. The consequence is the production of various thermal and optical properties. The activation of the optical response in the vacuum-UV might be useful for applications in nanoelectronics and photovoltaics. The heat capacity of the semiconductor monolayer is also higher than that of the metallic monolayer, which is identified them for thermal management and thermoelectric applications.