The observation of tunneling emission of electrons and holes from In(Ga)As/GaAs quantum dots in time-resolved capacitance measurements is reported. The electron and hole ground-state localization energies are determined as (290 +/- 30) meV and (210 +/- 20) meV, respectively. These energies are in excellent agreement with predictions from eight-band k center dot p theory. Based on the localization energies, we estimate the escape time for thermal excitation at room temperature as similar to 200 ns for electrons and similar to 0.5 ns for holes in case of a zero-electric-field situation. The electric-field dependence of the tunneling emission is investigated in detail.

The breakdown (BD) behaviour of Al/sub 2/O/sub 3/ dielectrics is investigated as a function of electrode material, stress voltage and thickness. Other than generally reported in the literature, two stable BD phases were found, even for metal electrodes, which is attributed to finite threshold energy for hard BD formation. This results in a limitation of the post BD current at product operation conditions and therefore opens up possibilities for target relaxation.

This paper reviews the concepts, status and challenges for the DRAM scaling down to 40nm. The technologies that are discussed are the DRAM cell capacitor structures and materials, as well as the cell transistor structures

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.

The hole confinement in type-II self-organized GaSb/GaAs quantum dots (QDs) was investigated by combining optical excitation and time-resolved capacitance spectroscopy. The experimental results indicate energy-selective charging even for type-II QDs. With increasing excitation energy the apparent hole activation energy decreases, which is attributed to light absorption in sub-ensembles of QDs with decreasing hole localization. The large localization energy of about 450meV and the possibility of optical-multiplexing makes type-II GaSb/GaAs QDs a potential material system for QD memory concepts.

We explore the Coulomb binding of electrons to holes confined to type-II GaSb self-assembled quantum dots. We demonstrate that at low laser power electrons are more weakly bound to holes trapped by the dots than to holes in the wetting layer. On the other hand, at high laser power the hydrogenic binding energy of dot excitons increases by more than a factor of two, and so exceeds that of wetting layer excitons. We attribute this to the strong binding of ‘core’ electrons to dots that are highly charged with holes by optical pumping.

Accumulated spectral hole burning is demonstrated for self-organized InAs/GaAs quantum dots (QDs) embedded in the space-charge region of a p–i–n diode. In two-color experiments, selective charging of QDs by resonant optical excitation is proved. A hole storage time of 1.5ms leads to saturation densities of only 0.5mW/cm−2. The results show the potential of inhomogeneously broadened ensembles of self-organized QDs for parallel optical storage. Additionally, spectral hole burning is used to identify the positive trion and to estimate the trion binding energy.

The impact of few-particle interactions on excited states of excitons localized in self-organized InxGa1-xAs/GaAs quantum dots (QD's), charged either with electrons or holes, is investigated. Excited-state absorption is probed size selectively by photoluminescence excitation spectroscopy improving the achieved resolution beyond the inhomogeneous broadening. Charging QD's embedded in suitable diode structures leads to nonlinear changes of the absorption characteristics for the individual excited-state transitions, enabling their unambiguous identification. Few-particle interactions lead to a renormalization of the excited-state transition energies, which ranges from a pronounced red shift to a blue shift depending on the excited-state transition and the type of spectator charge. The most pronounced effects occur charging the ground state of the QD's. The results are supported by eight-band k.p model calculations using a configuration-interaction scheme to account for the Coulomb interaction in the few-particle states.

We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes.

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.

The hole confinement of self-organized GaSb/GaAs quantum dots embedded in n(+)p-diodes is investigated experimentally by admittance spectroscopy. The highest thermal activation energy obtained, 400 meV, refers to only weakly charged quantum dots. Detailed bias-dependent investigations allow to study state- filling and Coulomb charging effects. State filling lowers the activation energy down to 150 meV in quantum dots charged with the maximum number of about 15 holes. The observed thermal activation barrier for GaSb/GaAs quantum dots is about twice as high as for structurally comparable InAs/GaAs quantum dots.

For memory structures based on optically induced charge in self-organized quantum dots, the concept of wavelength-domain multiplexing in the quantum dot ensemble is an essential prerequisite. The electric properties of quantum dots in various material systems as studied by time-resolved capacitance spectroscopy are summarized, and candidates suitable for future memory applications are discussed. By combining optical excitation and capacitance spectroscopy, direct evidence is obtained for energy-selective hole charge generation and storage in InAs/GaAs quantum dots. A clear dependence of the activation energy of the emitted holes on the energy of the excitation is observed.