Electronic Structure and Optical Properties of the Lonsdaleite Phase of   Si, Ge and diamond
  Crystalline semiconductors may exist in different polytypic phases with significantly different electronic and optical properties. In this paper, we calculate the electronic structure and optical properties of diamond, Si and Ge in the lonsdaleite (hexagonal-diamond) phase. We use an empirical pseudopotentials method based on transferable model potentials, including spin-orbit interactions. We obtain band structures, densities of states and complex dielectric functions calculated in the dipole approximation for light polarized perpendicular and parallel to the c-axis of the crystal. We find strong polarization dependent optical anisotropy. Simple analytical expressions are provided for the dispersion relations. We find that in the lonsdaleite phase, diamond and Si remain indirect gap semiconductors while Ge is transformed into a direct gap semiconductor with a significantly smaller band gap. 
Amrit De and Craig E. Pryor
cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.other quant-ph