Matched X-Ray Reflectometry and Diffractometry of Super-Multiperiod Heterostructures Grown by Molecular Beam Epitaxy

Resumo

Heterostructures with strongly-coupled multiple quantum wells, such as super-multiperiod superlattices with high perfection, may contain hundreds of layers, whose thicknesses can vary by orders of magnitude. The proposed method of characterization, consisting of the matched application of high-resolution X-ray diffractometry and reflectometry, makes it possible to study super-multiperiod structures of various types, including those with long periods and thin layers, and with high accuracy to determine the thicknesses of layers and roughness/diffuseness of boundaries. The difference between the expected and resulting thicknesses of the layers was 2–7% and 1–3% for the type I (InAs/GaAs) and type II (GaAs/Al_0.3Ga_0.7As) samples, respectively. Both types of structures are characterized by sharp interfaces with the RMS width of the transition layers of the order of several Å. Based on the best solution of inverse scattering problems, it is possible to determine with high accuracy both the morphology of the layers and their composition. That can be considered as the first step in the analysis of structures with a very large number of periods.