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 [001] GaAs with a 2° miscut toward the [101] direction (resulting in steps along the [010] 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 [010] direction to counter step alignment (along the [100] 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.
NPO-20695
This Brief includes a Technical Support Package (TSP).
Dislocation-induced changes in InxGa1-xAs Quantum dots
(reference NPO-20695) is currently available for download from the TSP library.
Don't have an account?
Overview
The document is a technical support package detailing research on dislocation-induced changes in InxGa1-xAs quantum dots (QDs), conducted by Rosa Leon at NASA's Jet Propulsion Laboratory. The study focuses on the spatial alignment of QDs in multilayer structures, which is crucial for enhancing the performance of quantum dot lasers and improving spatial ordering in self-forming QDs.
The research investigates multilayer arrays of QDs formed by alternately depositing thin layers of GaAs and In0.6Ga0.4As on semi-insulating [001] GaAs substrates with a slight miscut. This miscut creates steps along the [010] direction, which influences the alignment of the QDs. The study reveals a transition in the alignment of the QDs from step edge alignment along the [010] direction to counter step alignment along the [100] direction. This transition occurs after the deposition of the fifth quantum dot layer and is associated with the formation of a network of misfit dislocations at the In0.6Ga0.4As/GaAs interface.
Despite the presence of dislocations, the QDs exhibit strong near-infrared cathodoluminescence (CL) emission, indicating that the optical properties remain intact. The findings suggest that the alignment of QDs can be controlled through the manipulation of substrate miscut and the critical thickness of the layers, leading to improved optical performance without compromising structural integrity.
The document emphasizes the significance of these findings for the development of advanced quantum dot lasers and other optoelectronic devices. The research demonstrates a novel approach to achieving better spatial ordering in QDs, which is essential for enhancing device efficiency and performance.
Overall, this work contributes to the understanding of how dislocation dynamics can be harnessed to optimize the properties of quantum dot structures, paving the way for future innovations in nanotechnology and materials science. The research is set to be published in the journal "Applied Physics Letters," further disseminating these important findings to the scientific community.
