X-ray analysis of self-organized InAs/InGaAs quantum dot structure

We report on an X-ray study of an InAs/InGaAs/GaAs multi quantum dot stack grown by metalorganic chemical vapor deposition using grazing incidence reflectometry, high-resolution X-ray diffraction, reciprocal space mapping and pole figure analysis. No direct signal from the quantum dots is found by the high-resolution techniques. All rocking curves on different symmetric and asymmetric Bragg reflections can be simulated within the framework of dynamical theory assuming a perfect tretragonally distorted InAs/InGaAs/GaAs multiquantum well system. A pole figure analysis in the vicinity of the (113) and (022) reflections, however, reveals a signal from the quantum dots. There is a considerable indium enrichment in the quantum dots as compared to the wetting layer indicating a strong In-diffusion during their formation. Moreover, a strongly anisotropic diffuse scattering distribution with respect to the [110] and [1 (1) over bar 0] directions is found.