A report describes an experimental study of dislocation-induced spatial ordering of quantum dots (QDs) comprising nanometer-sized InxGa1–xAs islands surrounded by GaAs. Metastable hetero-epitaxial structures were grown by molecular-beam epitaxy of InxGa1–xAs onto n+ GaAs and semi-insulating GaAs substrates. Then the structures were relaxed during a post-growth annealing/self-organizing process leading to the formation of surface undulations that acted as preferential sites for the nucleation of QDs. Structural effects of annealing times and temperatures on the strain-relaxed InxGa1–xAs/GaAs and the subsequent spatial ordering of the QDs were analyzed by atomic-force microscopy and transmission electron microscopy. Continuous-wave spectral and time-resolved photoluminescence (PL) measurements were performed to study the effects, upon optical properties, of increased QD positional ordering, increased QD uniformity, and proximity of QDs to arrays of dislocations. PL spectral peaks of ordered QD structures formed on strain-relaxed InxGa1–xAs/GaAs layers were found to be narrower than those of structures not so formed and ordered. Rise and decay times of time-resolved PL were found to be lower at lower temperatures — apparently as a consequence of decreased carrier-transport times within the barriers surrounding the QDs.
This work was done by Rosa Leon of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category. NPO-30691.
This Brief includes a Technical Support Package (TSP).
Study of Dislocation-Ordered InxGa1-x/GaAs Quantum Dots
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Overview
The document presents a study on the effects of growth conditions, surface morphology, and surface strain on the formation of ordered quantum dot (QD) structures, specifically focusing on InAs islands. Conducted under the auspices of NASA's Jet Propulsion Laboratory, the research investigates how dislocation-induced spatial ordering influences the optical properties and carrier dynamics of these QDs.
The growth of the QD structures was achieved using Molecular Beam Epitaxy (MBE) on n+ GaAs and semi-insulating GaAs substrates. The process involved the deposition of a buffer layer followed by a compositionally graded InGaAs layer, and subsequent layers of InGaAs and AlGaAs. The aim was to create a metastable structure that would relax during post-growth annealing, leading to the formation of Cross-Hatched Patterns (CHPs) that serve as preferential nucleation sites for QDs.
Time-resolved photoluminescence (PL) was employed to analyze how the alignment of QDs and the introduction of dislocations affect their optical properties. The study found that the annealing process, which involved heating the structures at various temperatures and durations, played a crucial role in enhancing the optical characteristics of the QDs. Specifically, the annealing conditions were tailored to optimize the growth and arrangement of the QDs, thereby improving their performance in optical applications.
The document emphasizes the significance of understanding the interplay between growth conditions and the resulting QD structures, as this knowledge can lead to advancements in the development of optoelectronic devices. The findings suggest that ordered QD structures exhibit superior optical properties, which could be leveraged in various applications, including lasers, photodetectors, and quantum computing.
Overall, this research contributes to the broader field of nanotechnology by providing insights into the mechanisms that govern the growth and behavior of quantum dots, highlighting the potential for enhanced performance in future technological applications. The work underscores the importance of precise control over growth parameters to achieve desired optical characteristics in semiconductor nanostructures.
