Regensburg 1998 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 2: Poster I
HL 2.88: Poster
Montag, 23. März 1998, 10:30–19:00, A
Structural properties of Zn2−2x(CuIn)xS2 solid solution thin films obtained by EXAFS — •M. Fieber-Erdmann, E. Holub-Krappe, H. Rossner, V. Eyert, I. Luck, R. Scheer, and H.-J. Lewerenz — Hahn-Meitner-Institut, Abt. AS, TF und CG, Glienicker Str. 100, D-14109 Berlin
The solid solution system Zn2−2x(CuIn)xS2 attracts interest due to its optoelectronic properties. Recent experiments show a highly nonlinear dependence of the optical band-gap upon the alloying parameter x. In order to shed some light on the origin of this effect, bandstructure calculations were performed. They revealed the strong influence of the Cu 3d -states. At the same time the sensitivity of the electronic bandstructure to the anion displacement parameter u became obvious. Extended X-ray absorption fine structure (EXAFS) spectroscopy is well suited to elucidate such effects in solid solution systems. We report on EXAFS experiments performed at the E4 and R"OMO II stations at HASYLAB. As a result, we obtain three different bond lengths corresponding to nearest neighbour-distances between S and the metal ions (In, Cu, Zn). Metal-metal distances were also determined. To a first approximation, although the lattice parameters a and c vary as a function of the composition of the sample, the bond lengths remain constant. In addition, the anion displacement parameter u = 0.225(4) could be derived for pure CuInS2 . This allows to access the electronic structure and the bonding properties.