With laterally resolved photoemission spectroscopy, we obtained In and Ga surface concentration maps of InAs∕GaAs quantum dots. Our data demonstrate that the dot composition is neither pure InAs nor homogeneous InxGa1−xAs, but presents an In concentration increasing from the borders to the center of the dots. Besides, our observations suggest strong In segregation (x∼0.9) on the surface of the dots and of the surrounding wetting layer. Such segregation, well known for two-dimensional InAs∕GaAs growth, had not been directly observed so far on the dots, and should be taken into account to model size and composition of GaAs-overgrown structures.
Surface compositional maps of self-organized InAs/GaAs quantum dots were obtained with laterally resolved photoemission spectroscopy. We found a surface In concentration of about 0.85 at the center of the islands which decreases to 0.75 on the wetting layer. Comparison with concentration values found in the core of similar dots suggests a strong In segregation on the topmost surface layers of the dots and on the surrounding wetting layer. Furthermore, the morphological properties of the dots such as size and density have been measured with plan-view transmission electron microscopy and low energy electron microscopy.
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