Tem Investigation of Self-Organized Pbse Quantum Dots as a Function of Spacer Layer Thickness and Growth Temperature

The study of the morphology, lateral and vertical correlation of self-organized PbSe quantum dots in Pb1−xEux Te is presented. The samples consist of quantum dot superlattices of n periods of (PbSe/Pb1−xEux Te) grown on PbTe/(111) BaF2 by the S-K mode using MBE. The Pb1−xEux Te spacer thickness was varied from 34.3nm to 312nm and the growth temperature was varied between 335°C and 380°C. Our TEM results show very good lateral and vertical correlation of the dots. The dots form an array with either a/b/c/a/b/c/... or a/a/a/... vertical stacking sequence along the [111] growth direction. The stacking sequence is accurately controlled by the thickness of the Pb1−xEux Te spacer layer thickness and the growth temperature. The best a/b/c/... spatial correlation was obtained for temperatures around 380°C and spacer thickness of ˜40nm. The dots are highly strained and form triangular pyramids with (111) bases and (100) facets as observed by AFM. The shape of the dots also varied with the Pb1−xEux Te spacer thickness. An analysis of the spatial correlation of the dots' size and shape with respect to spacer thickness and growth temperature is presented.