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/${\mathrm{In}}_{0.2}$ ${\mathrm{Ga}}_{0.8}$As/GaAs strained layers. In the ${\mathrm{In}}_{0.2}$ ${\mathrm{Ga}}_{0.8}$As 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 ${\mathrm{In}}_{0.2}$ ${\mathrm{Ga}}_{0.8}$As is found to be broadened to about 5–10 atomic layers, while that of InGaAs on GaAs is about 2–4 layers broad.