Imperfections in (Ga_1-xAl_xAs)n₁-(GaAs)n₂/GaAs supperlattices as observed by X-ray diffraction techniques

Growth imperfections in (Ga_1-xAl_xAs)n₁-(GaAs)n₂/ GaAs superlattices, grown on GaAs(001) substrates, have been investigated by X-ray diffraction techniques coupling image and rocking-curve recording. The use of a synchrotron radiation source has enabled topographic images formed with very weak superlattice reflections to be obtained. The intensity distribution across the sample surface observed in such images has revealed two different types of superlattice defects: either overall gradients of both the average composition and period or islands showing different composition and period from the surrounding material. Since these parameters control the optoelectronic properties and particularly the gap value it is of primary importance to grow homogeneous samples and to have a technique able to detect inhomogeneities such as the ones described in the present work.