Monolayer-scale optical investigation of segregation effects in semiconductor heterostructures

An optical approach for the study of segregation effects on the interfaces of semiconductor heterostructures is implemented for InAs/GaAs. Pairs of identical ${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$ ${\mathrm{Al}}_{\mathit{y}}$As/GaAs quantum wells, in which an InAs monolayer is inserted at nominally symmetric positions in the well, are grown by molecular-beam epitaxy and studied by low-temperature photoluminescence. Such pairs of structures display marked band-gap differences, which highlight the asymmetric broadening of the InAs layer due to the surface segregation of indium atoms during the growth. Reliable information on the indium composition profile is gained on the monolayer scale. We greatly refine previous estimates of the broadening of the GaAs-on-InAs interface. We also demonstrate that the InAs-on-GaAs interface lies at its nominal position; this result gives a clear example of a kinetic freezing of segregation processes in semiconductor heterostructures, occurring here when InAs is deposited on GaAs.