The dependence upon the ZnSe cap-layer thickness, of defect configurations observed in CdSe/ZnSe quantum-dot structures, was studied by means of transmission electron microscopy and reflection high-energy electron diffraction. Samples were grown by means of molecular-beam epitaxy at 350C. The nominal thickness of the CdSe layers was about 3 monolayers, and the cap-layer thickness ranged from 3 to 60nm. In all of the samples, reflection high-energy electron diffraction revealed a transition from a 2-dimensional to a 3-dimensional growth-mode during CdSe deposition. Transmission electron microscopy showed that pairs of stacking faults lay on one of the 2 pairs of lattice planes: {(111) (111)} and {(111) (111)}. The stacking faults were bounded by Shockley partial dislocations. Both of the stacking faults which formed a pair originated from the same stair-rod dislocation, with a Burgers vector of 1/8{110} lying at the CdSe-6ZnSe interface within a Cd-rich island. By measuring the atomic displacements in the vicinity of the stacking faults, it was deduced that all of the stacking faults were intrinsic. At the line-of-contact of 2 stacking faults which belonged to different pairs, stair-rod dislocations were observed which had a Burgers vector of 1/3{100} and were inclined to the interface. The lengths of all of the dislocation lines, and the sizes of the stacking faults, increased with increasing ZnSe cap-layer thickness. It was found that the 2-dimensions to 3-dimensions transition, observed by reflection high-energy electron diffraction, was probably caused by defect formation and was analyzed with respect to strain relaxation in the CdSe layer.

Electron Microscopy Investigation of the Defect Configuration in CdSe/ZnSe Quantum Dot Structures. D.Litvinov, A.Rosenauer, D.Gerthsen, H.Preis: Philosophical Magazine A, 2002, 82[7], 1361-80