X-ray triple-crystal diffractometry of defects in epitaxic layers

Abstract

A new method is developed for calculating the correlation function of the random deformation in heteroepitaxic layers and superlattices from measurements of iso‐intensity contours of diffuse X‐ray scattering. The method is based on the optical coherence approach and kinematical diffraction theory. Structural models have been found that enable the correlation functions to be calculated for various types of randomly placed defects (mosaic blocks and random elastic deformation). The applicability of the method has been demonstrated by measuring the diffuse X‐ray scattering from a ZnTe layer grown on a GaAs substrate. The parameters characterizing the defects were obtained from a comparison of the calculated correlation function with theoretical models.

Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs

“…This is supported by the fitting of a mosaic block model to the CuMnAs/GaAs that shows good agreement with a model assuming ellipsoid blocks with lateral dimensions of 50 nm, vertical dimensions of 20 nm and RMS misalignment of 1.5°(red line in Fig. 2e) 28,29 . The much sharper spot produced by the CuMnAs on GaP (right inset) indicates a more coherent layer that no longer fits a mosaic block model well.…”

ZnSe/CdTe/ZnSe heterostructures

“…We attempted to extract such information by simulating the measured reciprocal space maps using kinematic diffraction theory and the mosaiccrystal model. 25 In this model, mosaic blocks of average size R are separated from each other by piled-up threading dislocations with the same Burgers vector. Specifically, the threading segments of the misfit dislocations create smallangle boundaries between adjacent mosaic blocks and the blocks are assumed to be rotated with respect to each other by an angle ⌬.…”

“…25 Simulations were performed assuming a spherical shape for the blocks with a single characteristic radius R. The values of R and of ⌬ were determined through a least-squares fit of the experimental data to the predictions of Eqs. ͑2͒-͑4͒.…”

X-Ray Diffraction in Distorted Crystals and Imperfect Multilayered Structures. A Theoretical Approach Based on Recursion Equations

“…In our calculations we used the Gaussian correlation function b x À x H Y 0Y z À z H exp Àx À x H 2 aL 2 x À z À z H 2 aL 2 z , where L xYz are the correlation lengths. This function was obtained in [28] for the description of the random deformation field generated, for example, by a random dislocation array. Figure 2 shows the reciprocal space maps for the central peak of the MS and the first satellites.…”