Local vibrational properties of GaAs studied by extended X-ray absorption fine structure

Abstract

Extended X-ray absorption fine structure (EXAFS) has been measured at both the K edges of gallium and arsenic in GaAs, from 14 to 300 K, to investigate the local vibrational and thermodynamic behaviour in terms of bond expansion, parallel, and perpendicular mean square relative displacements and third cumulant. The separate analysis of the two edges allows a self-consistent check of the results and suggests that a residual influence of Ga EXAFS at the As edge cannot be excluded. The relation between bond expansion, lattice expansion, and expansion due to anharmonicity of the effective potential is quantitatively clarified. The comparison with previous EXAFS results on other crystals with the diamond or zincblende structure shows that the values of a number of parameters determined from EXAFS are clearly correlated with the fractional ionicity and with the strength and temperature interval of the lattice negative expansion. © 2013 AIP Publishing LLC.

On EXAFS Debye-Waller factor and recent advances

“…One can conclude that, while in diatomic molecules the bond expansion hri is completely determined by the distribution asymmetry, in many-atomic systems the contributions of asymmetry and potential shift are comparable for nearestneighbours distances and the potential shift neatly prevails for outer-shell distances (Fornasini et al, 2004;Abd el All et al, 2012;Ahmed et al, 2013).…”

“…Actually, the anharmonic contributions to the pair potential are not negligible (Eisenberger & Brown, 1979), at least for the first coordination shell; bond expansion and third and fourth cumulants can be measured with good accuracy and are far from negligible (Dalba et al, 1999;Fornasini et al, 2004;Abd el All et al, 2013;Ahmed et al, 2013).…”

“…After some general methodological considerations presented in this section, in the following sections x4, x5 and x6 we illustrate the connection between dynamical parameters extracted from EXAFS (correlation functions, force constants, Einstein and Debye temperatures) and physical properties (such as crystal structure and bond ionicity) by comparing the results obtained for copper (Fornasini et al, 2004) and for a series of crystals with the diamond-zincblende structure with different degrees of ionicity: germanium (Dalba et al, 1999), GaAs (Ahmed et al, 2013), InP (Schnohr et al, 2009), CdTe (Abd el All et al, 2012) and CuCl (Vaccari et al, 2007).…”

“…The average distance hri is always larger than the crystallographic distance R c , owing to the effect of perpendicular vibrations (Busing & Levy, 1964;Willis & Pryor, 1975). Accurate measurements of the bond expansion hri can now be routinely performed, and can give interesting information on the local behaviour of negative thermal expansion materials Yokoyama & Eguchi, 2011;Abd el All et al, 2012;Ahmed et al, 2013). For a given scattering path, the second cumulant, or EXAFS DW exponent, is the variance of the distribution of path lengths; in particular, for single scattering (SS) paths,…”

“…The comparison of bond and crystallographic expansions allows the evaluation of the perpendicular MSRD (Dalba et al, 1995a;Kamishima et al, 1997). From parallel and perpendicular MSRD one can reconstruct the ellipsoid of relative vibrations of nearestneighbour atoms (Ahmed et al, 2013;Fornasini, 2015b). The high accuracy of measurements has allowed the detection of the tiny isotopic effects on the low-temperature values of the parallel MSRD in germanium (Purans et al, 2008).…”