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 st udies 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 h exagonal lateral ordering tendency, (II) for intermediate spacer thicknesse s, a well defined FCC-stacking with nearly perfect lateral hexagonal orderi ng is observed, and (III) for thick spacers, uncorrelated and laterally dis ordered superlattices are formed. The experimental data can be represented in a phase diagram that demonstrates that the different kinds of vertical c orrelations also give rise to a qualitatively different scaling behavior of the lateral dot distances versus spacer thickness. (C) 2001 Elsevier Scien ce B.V. All rights reserved.