Chapter 3: Strain and Composition Determination in Semiconductor Heterostructures by High-Resolution X-ray Diffraction

In this chapter, the basics of the method for measuring the strain and composition in two-dimensional structures by means of high-resolution x-ray diffraction techniques and laboratory x-ray sources are presented. The method of x-ray diffraction to determine the composition and strain in semiconducting alloys is introduced. Comparison of these results with those determined by other analytical techniques has allowed to measure a deviation from the linear Vegard law in several semiconducting alloys. The study of a two-dimensional quantum system composed of InGaAs wetting and capping layers in low-density quantum dot (QD) nanostructures is reported and the in-depth distribution of indium in the wetting layer is evaluated. Some of the most cited theories describing the strain release in semiconductor heterostructures are introduced. The theory is extended to composition-graded heterostructures, which are of great interest for obtaining virtual substrates or strain-engineered heterostructures. Experimental results in the case of GaAlSb/GaSb single heterostructures and InGaAs/GaAs composition-graded heterostructures are reported.