Nearly perfect 3D ordering in IV–VI quantum dot superlattices with ABCABC... vertical stacking sequence

Self-organization of PbSe islands in epitaxial PbSe/Pb1−xEuxTe superlattices is shown to result in a spontaneous three-dimensional ordering of the PbSe dots in a trigonal lattice with a fcc-like ABCABC vertical stacking sequence. From X-ray diffraction reciprocal space maps, the interlayer correlation direction of the PbSe dots is found to be inclined by 40° with respect to the [111] surface normal. Peak profile measurements in the reciprocal space maps yield a coherence length of the ordered regions of 300±100 nm in the lateral, and of 530±50 nm in the vertical direction. This corresponds to ordered regions that contain as many as 250 PbSe dots.