Strain-Dependent Electronic and Optical Properties of Dirac-Semimetal Monolayer BeN4

Abstract

In this study, the strain-dependent electronic and optical properties of BeN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> monolayer have been analyzed using first-principles calculations. Monolayer BeN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> is a semimetal with almost zero bandgap and an anisotropic Dirac cone. The linear dispersion relation corresponding to the Dirac cone yields high Fermi velocity, low carrier effective mass and extremely high carrier mobility in the monolayer and makes it suitable for high-speed nanoelectronic applications. However, a sizeable bandgap is essential for operation at room temperature. Both uniaxial (along armchair direction) and biaxial strain result in bandgap opening in the electronic band structure. Moreover, the linear dispersion relation is nearly retained upon straining. Uniaxial strain turns out to be more effective in tuning the bandgap of BeN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> . The bandgap can be increased to as much as 262.5 meV by application of uniaxial strain. On the other hand, with biaxial strain, a maximum bandgap of 68.7 meV could be achieved. The sizeable bandgaps achieved by strain engineering can pave the way to application of two-dimensional BeN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> in high-speed devices operating at room temperature. Moreover, the application of strain modifies the optical characteristics of the monolayer, resulting in an increase in the static dielectric constant and a shift in the first optical gap of the material. Furthermore, compressive and tensile strain enhances the absorption coefficient in the visible and infrared regions, respectively. The reflectivity and real refractive index can also be modified with strain. These results provide guidelines for developing optoelectronic devices based on BeN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> monolayer.