Interface segregation and clustering in strained-layer InGaAs/GaAs heterostructures studied by cross-sectional scanning tunneling microscopy

Interface roughness due to segregation and clustering has been studied in atomic detail for the first time, using a cross-sectional scanning tunneling microscope and its spectroscopic ability to distinguish In and Ga atoms in GaAs/In0.2{Ga}0.8$As/GaAs strained layers. In the ${In}0.2Ga0.8As layers, InAs is found to cluster preferentially along the growth direction with each cluster containing 2-3 indium atoms. Indium segregation induced an asymmetrical interface broadening. The interface of GaAs grown on In0.2{Ga}0.8$As is found to be broadened to about 5--10 atomic layers, while that of InGaAs on GaAs is about 2--4 layers broad.