Surface evolution and three-dimensional shape changes of SiGe/Si(0 0 1) islands during capping at various temperatures

The authors use a combination of atomic force microscopy and selective wet chemical etching of the Si capping layer to investigate both the surface and the three-dimensional SiGe/Si(0 0 1) island shape changes during capping at various temperatures. Different evolution paths are identified depending on the capping temperature. During the early stages of Si overgrowth at 450 °C, a moderate SiGe alloying occurs near the island apex. In the later stages, island burying begins through lateral growth of pyramid-like structures, which consist of pure Si. A comparison with previous overgrowth studies allows us to clarify the role of the initial island size in determining the surface evolution above buried islands. Island dissolution with material transfer to the wetting layer dominates upon capping at 580 °C. Finally, when the temperature during growth and capping is identical, the islands become flatter and wider indicating that the system starts to evolve towards an energetically preferred SiGe quantum well.