SURFACE SEGREGATION IN (GA,IN)AS GAAS QUANTUM BOXES/

Three-dimensional coherent islands formed during the highly strained g rowth of In(0.3)G(0.7)As on GaAs(001) are studied by scanning tunnelin g microscopy. High-resolution images evidence two different types of s urface reconstructions between the top and the bottom of the islands. While a 2x4 GaAs(001)-like reconstruction is observed on the wetting l ayer, the top layer exhibits the (2x4)alpha 2 phase, which is characte ristic of the InAs(001) reconstructed surface. This is the consequence of In surface segregation leading to the formation of a monolayer of InAs at the island top. Finally, photoluminescence experiments exempli fy the effect of segregation on the InxGa1-xAs/GaAs quantum box optica l properties.