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HL: Fachverband Halbleiterphysik

HL 43: Quantum dots and wires: Optical properties II

HL 43.9: Vortrag

Donnerstag, 28. Februar 2008, 16:15–16:30, EW 201

Time-resolved optical spectroscopy on epitaxially tailored quantum dots in the GaAs/AlGaAs material system — •Johanna Simon, Max Bichler, Jonathan Finley, and Gerhard Abstreiter — Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany

We report on spatially resolved optical spectroscopy of coupled quantum dots (QD) grown by 2-fold cleaved edge overgrowth (2-CEO). 2-CEO QDs are formed at the intersection of two perpendicular quantum wires and typically have weak confinement energies in the range of 7-15 meV. 2-CEO allows precise control over dot shape and location, thus making it particularly suitable for fundamental studies on coupled QD systems with precisely defined structural properties and inter-dot coupling.

Using spatially resolved µ-photoluminescence (µPL) we clearly identify emission from coupled QDs in a sample containing 22 identical QDs in a chain, with an inter-dot spacing of 30 nm. Time-resolved spectroscopy is used to probe their spontaneous emission dynamics and reveals multi-exponential decay transients. Most surprisingly, the longer time constant extends beyond 10 ns, a finding that is attributed to carrier delocalization, where the electron wave function is distributed over several dots, while the hole remains localized due to its higher effective mass. Systematic studies of the spontaneous emission dynamics as a function of inter-dot separation and the number of QDs in the array will be presented. In addition, perspectives for electrically tunable coupled QD systems are discussed.