Electronic Structures and Optical Properties of Uniform Ordered Hexagonal Ge0.5Si0.5 Alloys from First Principles

The electronic structures and optical properties of uniform ordered hexagonal Ge0.5Si0.5 alloys were investigated by the first-principle calculations. We first validated our approach for hexagonal Ge and Si, obtaining atomic geometries and band structures in excellent agreement with available experimental data. Then, the same approach was applied to predict electronic and optical properties of uniform ordered hexagonal Ge0.5Si0.5 alloys. The hex-Ge(0.5)Si(0.)5 alloy is a direct bandgap semiconductor. The dipole-forbidden or dipole-allowed transitions from the three highest valence bands (Gamma(+)(9v), Gamma(+)(7v+), Gamma(+)(7v-)) to the first (Gamma(-)(8c)) or second (Gamma(-)(7c)) lowest conduction band at Gamma point are obtained. The maximum absorption coefficient is close to 2 x 106 cm(-1). The three small absorption peaks probably originates from the transition from the Gamma(+)(9v), Gamma(+)(7v+) or Gamma(+)(7v-) to Gamma(-)(7c) band around the Gamma point, respectively.