Investigation of indium distribution in InGaAs/GaAs quantum dot stacks using high-resolution x-ray diffraction and Raman scattering.

Using high-resolution x-ray diffraction (HRXRD), Raman scattering, photoluminescence, and atomic-force microcopy, we investigated In_xGa_1-xAs/GaAs quantum dot (QD) stacks grown by molecular-beam epitaxy with nominal In contents of 0.30 and 0.35. The analysis of x-ray-diffraction rocking curves using symmetrical (004), asymmetrical (113), and quasiforbidden (002) reflections within the framework of dynamical theory allowed us to determine the average values of strains parallel and perpendicular to the growth direction. We also measured nonuniform In profiles in the In_xGa_1-xAs layers along the growth direction. This observation confirms the important role of surface segregation of In atoms and interdiffusion of Ga atoms from GaAs layers in the formation of In_xGa_1-xAs QDs. Both HRXRD and Raman scattering in In_xGa_1-xAs/GaAs-stacked QD structures demonstrate that the InGaAs inserts in these structures can be modeled effectively as sublayers with two different compositions: sufficiently thick In_xGa_1-xAs sublayer with the In concentration lower than the nominal one, which includes the thin layer of InGaAs islands with the In concentration much higher than the nominal one. [ABSTRACT FROM AUTHOR]