Cross-sectional scanning tunneling microscopy of InAs/GaAs(001) submonolayer quantum dots

Cross-sectional scanning tunneling microscopy (X-STM) was employed to characterize the InAs submonolayer quantum dots (SMLQDs) grown on top of a Si-doped GaAs(001) substrate in the presence of (2 x 4) and c(4 x 4) surface reconstructions. Multiple layers were grown under different conditions to study their effects on the formation, morphology, and local composition of the SMLQDs. The morphological and compositional variations in the SMLQDs were observed by both filled and empty-state imaging. A detailed analysis of indium segregation in the SMLQD layers was described by fitting the local indium-concentration profile with a standard segregation model. We observed a strong influence of the arsenic flux over the indium incorporation and formation of the SMLQDs. We investigated the well-width fluctuations of the InGaAs quantum well in which the SMLQDs were formed. The well-width fluctuations were small compared to the more pronounced composition fluctuations in all the layers. The lateral compositional variations lead to the formation of indium-rich clusters which can act as quantum dots and yield charge-carrier confinement.