Phase diagram of lateral and vertical ordering in self-organized PbSe quantum dot superlattice grown MBE

Self-organized lateral and vertical ordering in PbSe/Pb1-xEuxTe quantum dot superlattices is investigated as a function of Pb1-xEuxTe spacer thickness. From cross-sectional transmission electron and atomic force microscopy studies we End the occurrence of three differently ordered dot phases due to changes in the vertical Jot correlation at certain spacer thicknesses: (I) for small spacer thicknesses. the dots are vertically aligned with a weak hexagonal lateral ordering tendency, (II) for intermediate spacer thicknesses, a well defined FCC-stacking with nearly perfect lateral hexagonal ordering is observed, and (III) for thick spacers, uncorrelated and laterally disordered superlattices are formed. The experimental data can be represented in a phase diagram that demonstrates that the different kinds of vertical correlations also give rise to a qualitatively different scaling behavior of the lateral dot distances versus spacer thickness. (C) 2001 Elsevier Science B.V. All rights reserved.