3D hexagonal versus trigonal ordering in self-organized PbSe quantum dot superlattices

Self-organized vertical and lateral ordering in PbSe/PbEuTe quantum dot superlattices grown by molecular beam epitaxy is investigated by synchrotron X-ray diffraction and atomic force microscopy. For small PbEuTe spacer thicknesses, the dots are ordered hexagonally in the lateral direction and vertically aligned along the growth direction. This yields an overall 3D hexagonal lattice of dots. For larger spacer thicknesses an FCC-like dot stacking is formed, resulting in the formation of a 3D trigonal dot lattice. From the analysis of the X-ray diffraction spectra the ordering is significantly better for the trigonally ordered dot samples.