Structural, electronic, and optical properties of ordered Si1−Ge C alloys: A first principles study

Abstract

• Structural, electronic, and optical properties of ordered Si 1 − x Ge x C alloys by first principles calculations. • The lattice constants show a linear dependence on the composition x . • The bulk and shear moduli reduce linearly as the increase of composition x . • The indirect to direct band gap transition is result from the symmetry change. • It is proposed that the composition dependent refractive index follows a quadratic equation. The effect of germanium content on the structural, electronic, and optical properties of ordered Si 1 − x Ge x C alloys ( x = 0, 0.25, 0.5, 0.75, 1) has been systemically investigated in the present work by using first principles calculations based on the density functional theory. The calculated lattice parameters, bulk and shear moduli which exhibit linear dependences on the composition x follow the Vegard’s law and are fitted by linear interpolation. The electronic band structure calculations performed by the application of HSE03 functional reveal that Si 1 − x Ge x C alloys are all wide band gap semiconductors, among which Si 0.75 Ge 0.25 C and Si 0.25 Ge 0.75 C have direct band gaps. The substitution of Ge for Si changes the symmetry of zb-SiC unit cell, giving rise to the indirect to direct band gap transition. The composition dependent static optical functions, such as dielectric constants, refractive index and Plasmon energy are discussed.