Biomedical subjects

D Bimberg

Publications and source records attributed to D Bimberg.

At least 19 recordsLinked to original sources

PubMed2005

Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots.

A systematic variation of the exciton fine-structure splitting with quantum dot size in single quantum dots grown by metal-organic chemical vapor deposition is observed. The splitting increases from to as much as with quantum dot size. A change of sign is reported for small quantum dots. Model calculations within the framework of eight-band theory and the configuration interaction method were performed. Different sources for the fine-structure splitting are discussed, and piezoelectricity is pinpointed as the only effect reproducing the observed trend.

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PubMed2004

Hierarchical self-assembly of GaAs/AlGaAs quantum dots.

A novel structure containing self-assembled, unstrained GaAs quantum dots is obtained by combining solid-source molecular beam epitaxy and atomic-layer precise in situ etching. Photo-luminescence (PL) spectroscopy reveals light emission with very narrow inhomogeneous broadening and clearly resolved excited states at high excitation intensity. The dot morphology is determined by scanning probe microscopy and, combined with single band and eight-band k.p theory calculations, is used to interpret PL and single-dot spectra with no adjustable structural parameter.

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PubMed2004

Tunable metastability of surface nanostructure arrays.

A Fokker-Planck equation is used to model the coarsening of surface nanostructure arrays. Metastable states are identified which are associated with a narrow size distribution and a coverage dependent mean island size. This is a general feature linked to nanostructures which, as a function of island size, are associated with a minimum in formation energy per atom and a positive chemical potential gradient. This has important implications for the self-organization of quantum dots.

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PubMed2003

Metastability of ultradense arrays of quantum dots.

We present a linear stability analysis of ultradense arrays of coherently strained islands against Ostwald ripening. Surprisingly, short-range elastic interactions are found to overcome the destabilizing contribution of surface energy, leading to a metastable array of quantum dots. Simulations of Ostwald ripening kinetics directly verify the existence of this metastable regime and confirm the nature of the most unstable mode for subcritical island coverage.

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PubMed2002

Relaxation and dephasing of multiexcitons in semiconductor quantum dots.

We measure the dephasing time of ground-state excitonic transitions in InGaAs quantum dots under electrical injection in the temperature range from 10 to 70 K. Electrical injection into the barrier region results in a pure dephasing of the excitonic transitions. Once the injected carriers fill the electronic ground state, the biexciton to exciton transition is probed and a correlation of the exciton and biexciton phonon scattering mechanisms is found. Additional filling of the excited states creates multiexcitons that show a fast dephasing due to population relaxation.

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PubMed2001

Self-assembled quantum dots: crossover from kinetically controlled to thermodynamically limited growth.

By means of kinetic Monte Carlo simulations of the self-organized growth of quantum dots in strained semiconductor systems we resolve the seemingly contradictory features of kinetic versus thermodynamic behavior, e.g., with respect to the temperature dependence of the average dot size and their dispersion. We show that the size distribution immediately after deposition is kinetically controlled, with smaller islands for lower temperatures and larger islands for higher temperatures. For longer simulation times the kinetics leads to equilibration, and a crossover effect between the size distributions occurs, which is in good agreement with the predictions of thermodynamics.

Journal Article↗

PubMed2001

Ultralong dephasing time in InGaAs quantum dots.

We measure a dephasing time of several hundred picoseconds at low temperature in the ground-state transition of strongly confined InGaAs quantum dots, using a highly sensitive four-wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.

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PubMed1996