Electric-field-induced charge-density variations in covalently bonded binary compounds - art. no. 165205

Extended data sets for the relative intensity variation of x-ray Bragg refl ections of GaAs and ZnSe caused by an external electric field were collecte d using a modulation demodulation technique. In particular, the functional dependence of the intensity variation on field strength and wavelength of t he synchrotron radiation was determined. The wavelength dependence allows t o determine the phases of the difference-structure factors. An interpretati on of all data using a semiempirical model leads to the following conclusio ns: The main contribution to the measured effects comes from a displacement of the anion sublattice relative to the cation sublattice. The response of the electron density to an external electric field is negligibly small acc ording to density functional theory calculations with both, clamped and ''f ree'' ions. This effect is much smaller than the redistribution of the elec tron density in the bond region associated with the displacements of the at oms causing a change in overlap. The dependence of the sublattice displacem ent on the strength of the external electric field E parallel to [111] is e stimated to be 1.5x10(-8) Angstrom /V mm(-1) for GaAs and 13.5x10(-8) Angst rom /V mm(-1) for ZnSe. For the mainly covalent GaAs the inverse piezoelect ric effect can be explained by this bond-length variation, in contrast to t he much more ionic compound ZnSe for which this is not the case.