F. Guffarth

Radiation hardness of InGaAs/GaAs quantum dots

The interaction between point defects in the matrix and excitons localized in self-organized InGaAs/GaAs quantum dots is investigated for structures irradiated by protons. The exciton ground state is demonstrated to be unaffected by radiation doses up to 1014 p/cm2. The close proximity of radiation-induced defects leads to a strong nonmonotonous temperature dependence of the luminescence yield: Carriers are lost via tunneling from excited quantum dot states to irradiation-induced defects below ∼100 K, whereas at higher temperatures, carriers escape to the barrier and are captured by defects.

State-filling and renormalization in charged InGaAs/GaAs quantum dots

Abstract Few-particle effects have been studied for charged InGaAs/GaAs quantum dots (QDs) by means of size-selective photoluminescence excitation spectroscopy (PLE). The effects of spectator electrons on the electronic properties, in particular exciton transitions in the near infrared spectral region, are investigated. The characteristic quenching of excitation channels due to state-filling with increasing charging allows to identify excited exciton transitions and to correlate the observed renormalization of the transition energies to the QD population.

Wavelength selective charge accumulation in self-organized InAs/GaAs quantum dots

Wavelength selective charging of a QD sub-ensemble is demonstrated, presenting a basis of future wavelength dependent parallel optical memory. High-resolution saturation spectroscopy in two-colour photocurrent experiments is used to investigate the binding energy of the positively charged trion complex as well as the temperature dependence of the coupling to acoustic phonons.

Local Phonon Modes in InAs/GaAs Quantum Dots

Local optical phonons in self‐organized InAs/GaAs quantum dots (QDs) are investigated by Raman scattering under resonant excitation of the QD ground state transition. All QD sample structures, including single and stacked QD layers, pure InAs and InxGa1−xAs QDs as well as InAs QDs overgrown by GaAs and InxGa1−xAs quantum wells, show an interface mode at ∼36 meV, a LO‐like confined InAs QD mode at ∼33 meV and a TO‐like confined InAs QD mode at ∼31 meV. For all samples the interface mode shows the strongest exciton‐phonon coupling, followed by the QD LO mode.

Correlation of structural and optical properties of self-organized quantum dots

Interaction between strongly localized charge carriers in zero-dimensional systems like quantum dots (QD) depends sensitively on the geometrical roperties of the dots. The recently observed monolayer splitting with eight well resolved peaks (in low excitation photoluminescence (PL)) together with eight-band kp theory as the appropriate tool for modeling electronic and optical properties offers direct spectroscopic access to details of the QD morphology. By this achievement it became possible to link single-dot spectra obtained by cathodoluminescence measurements via the exciton transition energy to structural properties of the probed QD. In view of theory this situation constitutes an ideal starting point to study few-particle interactions for realistic InAs QDs as a function of their structural properties. This is done using the configuration interaction method. The wavefunctions are obtained from eight-band kp calculations of single-particle states including explicitly piezoelectric effects in the confinement potential.