Lateral periodicity in highly-strained (GaIn)As/Ga(PAs) superlattices investigated by X-ray scattering techniques

In this work we investigate the lateral periodicity of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of X-ray scattering techniques. The multilayers were grown by metalorganic Vapour phase epitaxy on (001)GaAs substrates, which were intentionally off-oriented towards the [011]-direction. The substrate off-orientation and the strain distribution was found to affect the structural properties of the superlattices inducing the generation of laterally ordered macrosteps. Several high-resolution triple-crystal reciprocal space maps, which were recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction and contour maps of the specular reflected beam collected in the vicinity of the (000) reciprocal lattice point, are reported and discussed. The reciprocal space maps clearly show a two-dimensional periodicity of the X-ray peak intensity distribution which can be ascribed to the superlattice periodicity in the direction of the surface normal and to a lateral periodicity in a crystallographic direction coinciding with the miscut orientation. The distribution and correlation of the vertical as well as of the lateral interface roughness was investigated by specular reflectivity and diffuse scattering measurements. Our results show that the morphology of the roughness is influenced by the off-orientation angle and can be described by a 2-dimensional waviness.

CALCULATIONS OF THE EIGENVALUES OF PURE QUADRUPOLE INTERACTION IN MOSSBAUER-EFFECT STUDIES

Two approximate formulae to calculate the eigenvalues of pure quadrupole interaction in Mossbauer effect studies have been proposed and the eigenvalue coefficients in the formulae have been given for various excited states and ground states of the nucleus with different spin. All the eigenvalues of pure quadrupole interaction between both excited state and ground state of nucleus with spin I = 3/2 divided-by 9/2 and the electric-field gradient with different asymmetry parameter (eta = 0 divided-by 1.0) have been calculated by these formulae. The results show that the accuracies in all the calculations are more satisfactory or same in comparison with those obtained by the formula of Shenoy and Dunlap, especially when the asymmetry parameter of electric-field gradient is larger than 0.8 for the nucleus with spin I = 5/2.