Atomic Force Microscopy and Transmission Electron Microscopy Study of Self-Organized Ordering in Vertically Aligned PbSe Quantum Dot Superlattices

Self-organized lateral ordering is studied for PbSe/Pb 1- x Eu x Te quantum dot superlattices as a function of spacer thickness using atomic force microscopy and transmission electron microscopy. It is found that a pronounced hexagonal lateral ordering tendency exist not only for fcc- stacked superlattices but also for those with vertical dot alignment. For the latter case, a best in-plane ordering is observed for Pb 1- x Eu x Te spacer thicknesses around 160 Å. This is accompanied by a pronounced narrowing of the size distribution to values as low as ±8%. The resulting in-plane dot separations and dot densities are tunable by changes in spacer thickness. Similar marked changes are also found for PbSe dot shape as well as the dot sizes. This provides additional means for the tuning of the optical and electronic properties of the dots.