EXAFS studies of semiconductors and ferroelectrics

XAFS spectroscopy, which includes the investigations of both Extended X-ray Absorption Fine Structure (EXAFS) and X-ray absorption Near-Edge Structure (XANES), is a powerful technique for structural investigations. It is widely used in physics, materials science, chemistry (especially in catalysis and coordination chemistry), biology, geochemistry and environmental science. It can be applied to the studies of not only crystalline solids, but also to studies of various disordered, nanocrystalline, amorphous and liquid systems.

In our laboratory we use EXAFS to study the local environment of isovalent and nonisovalent impurities in narrow-gap IV-VI semiconductors with a particular emphasis to off-center impurities which can induce the ferroelectric phase transition in these crystals. We study the mechanisms in which different doping impurities influence the ferroelectric properties such as the phase transition (Curie) temperature. An interesting result of this work was the discovery of a new class of off-center ions - off-center ions of large size. Lead (Pb) and tin (Sn) impurity atoms in germanium telluride (GeTe) can serve as examples.

Our main interest now is paid to determination of the parameters of three-dimensional (3D) multiwell potential for some off-center atoms from EXAFS data. This potential is characterized by strong anharmonicity and anisotropy, so we cannot use standard approach based on the cumulant expansion method. Our approach uses exact three-dimensional integration of the atomic distribution function that is calculated within the quantum statistical approach from the wave functions obtained from numerical solution of the Schroedinger equation for 3D anharmonic anisotropic potential.

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Physics of Semiconductors division