Correlation lengths in stacked InAs quantum dot systems studied by cross-sectional scanning tunnelling microscopy

We have studied the influence of the InP spacer layer thickness on stackedInAs/InP quantum dots, using cross-sectional scanning tunnellingmicroscopy. We show that for a spacer layer thickness of up to 30 nm, thequantum dots are spatially correlated but for a separating distance of 50 nmthe vertical ordering of the dots is lost. These values are the same aspreviously found for quantum dots in the InAs/GaAs system despite the largedifference in lattice mismatch between the InAs/GaAs (7%) and InAs/InP(3%) systems. We show that the apparent similarities can be understood by acombination of intermixing in the dots and differences in dot size. Finally,we demonstrate that the size of the quantum dots is affected by their verticalcorrelation.