A report describes an experimental investigation that revealed a previously unknown type of spatial alignment of quantum dots (QDs) in InxGa1 -xAs/GaAs multilayer structures. Multilayer arrays of QDs (in the form of nanometer-sized InxGa1-xAs islands) were formed by alternately depositing 10-nm-thick layers of GaAs and 5-molecule-thick layers of In0.6Ga0.4As/GaAs on substrates of semi-insulating  GaAs with a 2° miscut toward the  direction (resulting in steps along the  direction). Specimens were examined by electron microscopy and cathodoluminescence (CL) spectroscopy. The QDs were observed to undergo a transition between step edge alignment along the  direction to counter step alignment (along the  direction). This transition apparently occurred when (or soon after) the fifth quantum-dot layer was deposited, and is apparently associated with the onset of a network of misfit dislocations at the In0.6Ga0.4As/GaAs interface. A change to larger QDs in smaller concentrations was also observed after formation of the network of dislocations. Strong near-infrared CL emission from the QDs was observed, despite the presence of dislocations.
This work was done by Rosa Leon of Caltech for NASA's Jet Propulsion Laboratory. To obtain a copy of the report, "Dislocation-induced Changes in Quantum Dots: Step Alignment and Radiative Emission," access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.