INTERFACE SEGREGATION AND CLUSTERING IN STRAINED-LAYER INGAAS/GAAS HETEROSTRUCTURES STUDIES 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/In0.2Ga0.8As/GaAs strained layers. In the In0.2Ga0.8As 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 as grown on In0.2Ga0.8As is found to be broadened to about 5-10 atomic layers, while that of InGaAs on GaAs is about 2-4 layers broad.