Composition evaluation of InxGa1−xAs Stranski-Krastanow-island structures by strain state analysis

The compositional analyses of ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}$ /GaAs (001) island structures grown by molecular beam epitaxy at a substrate temperature of 560 $°$ C with nominal In contents of $\text{x=60\%}$ and 100% are presented on the basis of high resolution transmission electron microscopy micrographs. The linear dependence of the lattice parameter on the In content (Vegard’s law) is exploited to quantitatively derive composition profiles on an atomic scale by measuring local lattice parameters and displacements. The relaxation of the thin transmission electron microscopy specimen is taken into account by the accurate thickness determination using the quantitative analysis of the information from transmission electron micrographs procedure. The final evaluation step consists of finite element modeling with the appropriate sample geometry, where the In distribution is chosen to obtain the best fit between experimental and simulated displacements. The observed In content is significantly smaller than the nominal In concentration which is due to segregation of In and diffusion of Ga from the GaAs buffer into the island during the growth. The measured mean In concentration of the islands with a nominal In content of 60% (100%) is 24% (45%).