Nonuniform composition profile in In0.5Ga0.5As alloy quantum dots

We use cross-sectional scanning tunneling microscopy to examine the shape a nd composition distribution of In0.5Ga0.5As quantum dots (QDs) formed by ca pping heteroepitaxial islands. The QDs have a truncated pyramid shape. The composition appears highly nonuniform, with an In-rich core having an inver ted-triangle shape. Thus the electronic properties will be drastically alte red, relative to the uniform composition generally assumed in device modeli ng. Theoretical analysis of the QD growth suggests a simple explanation for the unexpected shape of the In-rich core.