Laboratoire Pierre Aigrain - UMR 8551

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Alexandre Freundlich (Center for Advanced Materials, University of Houston)

Following a brief introduction to ongoing research activities at the Center for Advanced Material and its Photovoltaics and Nanostructures Laboratory, the presentation will provide a more detailed overview of the effort in the understanding and development of self-assembled quantum dots. In particular within the context of the archetype InAs/GaAs self-assembled quantum dot system, the presentation will discuss an in situ, methodology based on the analysis of reflection high energy electron diffraction (RHEED) patterns and demonstrate its ability for real time and simultaneous determination of the quantum dots facet orientations, average size (height), strain profile, and dot-density during the molecular beam and chemical beam epitaxy growth. Atomistic kinematic diffraction calculations, RHEED measurements, and ex-situ atomic force microscopy experiments are combined for a systematic analysis and correlation of RHEED diffraction patterns with different QD heights and distributions. In addition to RHEED’s more common lattice spacing measurement features, which allows the monitoring of strain and its relaxation, here it is shown that an unambiguous determination of dot-facet orientations can be afforded through the multi-azimuthal analysis of the chevron angles. Furthermore it is shown that the evolution of the average dot height (size) and dot-surface coverage (density) can be monitored real time and during growth through the analysis of the periodicity and amplitude of the intensity fringes along chevron tails. Finally few illustrations of the strength of the methodology in assessing the growth kinetics and in monitoring the evolution of structural parameters in complex quantum dot stackings will presented.