DIFFUSE-SCATTERING, SIZE EFFECT AND ALLOY DISORDER IN TERNARY AND QUATERNARY-III-V COMPOUNDS

The diffuse intensity present in the X-ray and electron diffraction patterns of the ternary and quaternary III-V alloys with mixed sublattice(s) hosting atoms of different covalent radii is studied in detail. It consists of portions of (110)-oriented reciprocal planes passing slightly away from the main diffraction spots. Using a valence force field model to calculate the static atomic displacement field, and the kinematical approximation for diffraction, it is shown that the experimental patterns are compatible with a total lack of correlation between the occupations of the various sites of the mixed sublattice(s) without, however, excluding the existence of some moderate ordering or clustering. The characteristic intensity distribution observed is interpreted in terms of the correlated atomic displacements from the average lattice induced in its vicinity by any atom belonging to a mixed sublattice. The particularly strong anisotropy of this size effect is related to the covalent character of the III-V alloys. © 1990 Taylor & Francis Ltd.