The self-organization of pyramidal PbSe islands that spontaneously form during strained-layer epitaxial growth of PbSe/Pb1-xEuxTe (x = 0.05 to 0.1) superlattices results in the formation of three-dimensional quantum-dot crystals. In these crystals, the dots are arranged in a trigonal lattice with a face-centered cubic (fcc)-like A-B-C-A-B-C vertical stacking sequence. The lattice constant of the dot crystal can be tuned continuously by changing the superlattice period. As shown by theoretical calculations, the elastic anisotropy in these artificial dot crystals acts in a manner similar to that of the directed chemical bonds of crystalline solids. The narrow size distribution and excellent control of the dot arrangement may be advantageous for optoelectronic device applications.

Vertical and lateral ordering of quantum dots in superlattices is shown to be determined by the elastic anisotropy of the matrix material and by the growth orientation. For large anisotropies, complicated dot stacking sequences with correlations inclined to the growth axis may be formed, and the lateral ordering tendency is much stronger than for isotropic materials.

The tuning of lateral and vertical correlations in self-organized PbSe/Pb 1-xEu xTe quantum dot superlattices by changes in the spacer thicknesses is demonstrated and shown to be due to finite size effects in the dot-dot interactions. As a consequence, different dot arrangements such as vertically aligned dot columns or fcc stacking are obtained for a single material system without changes in growth conditions. The different dot superstructures are shown to exhibit a different scaling behavior of the lateral versus vertical dot separation, as well as a different evolution of dot sizes and shapes.

Direct growth of tensile-strained PbSe quantum dots by molecular beam epitaxy on 5.5% lattice mismatched PbTe (111) is investigated by atomic force microscopy and in situ reflection high energy electron diffraction. After wetting layer formation, two types of PbSe islands are formed distinguishable in size and ordering behavior. All islands exhibit a well defined pyramidal shape with triangular base and steep (100) side facets. In addition, the dots exhibit a remarkably narrow size distribution with a relative variation of height and width as low as ±7%.