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  • University of Cincinnatti

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An Indium cell was recently introduced into our molecular beam epitaxy system. This opened up for growth of self-assembled quantum dots based on lattice mismatched InGaAs on GaAs. These solid-state zero-dimensional structures, with optical properties resembling those found in atoms, are promising for future optical components with high material gain, low threshold current for laser action and fast operation due to suppressed heating dynamics. With standard photoluminescence techniques combined with high spatial resolution, we study individual dots i.e. their line width, spectra and optical density. On specially prepared samples we can in addition probe the physical density of quantum dots with atomic-force microscopy for varying growth conditions. The line spectrum of individual dots is not yet well understood. The complication is that shape and strain anisotropies play a major role and are hard to separate with linear spectroscopy. We are therefore currently using nonlinear second harmonic spectroscopy to probe symmetries of dots to separate these effects and provide much better understand of individual quantum dot spectra. To gain more information of carrier dynamics and relaxation in these types of quantum dots, the high spatial resolution must be combined with spectroscopic techniques having high temporal resolution. One useful technique is based on coherent control that utilizes phase-locked laser pulses. With an actively stabilized Mach-Zender interferometer we can directly probe coherence times of individual quantum dot states as an example. In this context we can follow the time evolution of a wave packet composed of quantum dot states reflecting the atomic-like optical properties of this solid state system. Since disorder in nanostructures complicates the physics, it is important to find simpler model systems.
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ID: 2263661