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

The effect of germanium content on the structural, electronic, and optical properties of ordered Si1−xGexC 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 Si1−xGexC alloys are all wide band gap semiconductors, among which Si0.75Ge0.25C and Si0.25Ge0.75C 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.