Diffraction anomalous fine structure of forbidden reflection of super-ordered GaInP

We used DAFS to probe super-ordered domains in InGaP/GaAs epitaxial growth. The sample was lattice matched InGaP epitaxially grown on GaAs with a substrate miscut angle of 6 degrees with respect to the (001) direction. InGaP epi-layer exhibited (111)-type alloy ordering, of alternating InP and GaP-like planes and giving rise to a (-5/2, 5/2,-5/2) Bragg peak reflection which becomes allowed. Structural data can be extracted, at the same time, for the surroundings of Gallium in the bulk and in the epi-layer from allowed reflections, while the forbidden reflection gives structural details around Gallium in the ordered domains. Difference with the bulk InGaP Fourier transform confirms the symmetry selectivity of chosen reflections for the super-ordered domains.