CALCULATED BAND-STRUCTURE OF ZINCBLENDE-TYPE SNGE

The band structure of SnGe in the zinc-blende structure is calculated using the scalar-relativistic linear-muffin-tin-orbital method in conjunction with the density-functional scheme. The local-density approximation is empirically corrected by means of an external potential. Special emphasis is placed on the effects of inversion asymmetry, such as ionicity and spin splittings. An equilibrium volume is found at a lattice constant of a0 = 6.0630 angstrom, which is very close to the average of the lattice constants of Ge and alpha-Sn. At the corresponding volume, the calculated direct gap is +0.085 eV. For a slightly larger lattice constant, corresponding to the average volumes of the two constituents, SnGe should have a ''negative'' gap of nearly the same magnitude, and thus have an inverted band structure similar to alpha-Sn. The polarity of the Ge-Sn bond is calculated to be alpha(p) = 0.2. The transverse effective charge is e(T)* = 0.47, Sn being positive (''cation'').