First-principles study of stability, band structure, and optical properties of the ordered Ge0.50Sn0.50 alloy

All electron density functional theory calculations were performed on the o rdered Ge0.50Sn0.50 alloy in the zinc-blende phase to study its structural, electronic, and optical properties along with its stability with respect t o the elemental components. We employed a linear combination of atomic orbi tals approach for calculations in which the Bloch functions were constructe d as linear combinations of atom-centered Gaussian orbitals. The calculated results show a relative stability of the GeSn alloy in the zinc-blende pha se for which the lattice constant and bulk modulus are predicted to be 6.20 Angstrom and 53 GPa, respectively. Analysis of band structure and density of states shows the cubic-ordered alloy to be a direct-gap semiconductor wi th a small band gap. The optical properties, such as dielectric constant an d plasmon energy of the cubic alloy, appear to be about the average of the respective values in its elemental components. (C) 1999 American Institute of Physics. [S0003-6951(99)01452-7].