W0011

Electric-field Induced Valence Charge Density Response in GaAs and ZnSe. Ullrich Pietsch, Jochen Stahn, Adreas Pucher, Anke Daniel Institute of Physics, University of Potsdam, Germany

Most of the ground-state properties of solid state can be described more or less completely using different ab-initio methods (DFT, HF...). This is not longer valid for describing dynamical properties. In particular the improvement of concepts for describing non-linear screening in semiconductors requires new experiments to investigate the charge density response under external perturbation. We measured the variation of particular bond-charge-sensitive X-ray structure amplitudes of GaAs and ZnSe under influence of an external electric field. The experiments have be performed at the beamline D3 at HASYLAB (Hamburg, Germany) choosing a wave-length very close to the K-absorption edge of As and Se, respectively. Using a modulation technique we could determine a relative change in X-ray scattering intensities of the order of 1% for the low indexed (222) reflections but smaller than 0.1% for higher indexed ones (442,662,666...) applying an electric field up to E= 30 kV/cm. Evaluating the field-strength dependence of the intensity variation we find a strictly linear behavior versus E at the (222) but a rather E<= dependence for higher-indexed reflections. The linear effect can completely described in terms of a bond-charge transfer between bonds arranged parallel and oblique with respect to the applied field direction. The second effect may be explained by the E-field induced dipole-charges close to the ionic cores. This work was supported by the BMBF (grant 05 647IPA) and the EC (grant CHRX-CT93-0155)