Direct determination of elastic strain in strained-layer superlattices by high-angle x-ray interferences

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Abstract
A novel nondestructive technique for the determination of elastic strains in strained-layer superlattices, which is based on x-ray diffractometry, is described. For the first time, the relative inclination of equivalent lattice planes due to elastic misfit strain in superlattices with small periods exhibiting high-angle x-ray interferences was measured. Sets of theta-twotheta scans with a narrow detector slit were performed for various lattice planes of one crystallographic zone starting at different theta offsets. The value of the angle theta, at which the maximum peak intensity is observed, is a direct measure for the distortion of the strained superlattice layers. It allows the determination of the complete strain status in three dimensions in the individual constituents separately even without knowing the unstrained lattice constant. In addition, this technique is used in the wide temperature range of 10–350 K. It is applied to a study of PbTe-PbSnTe superlattices grown on cleaved (111)-BaF2 in order to determine both the elastic misfit and the temperature-dependent substrate induced strains.