We identify fundamental mechanisms of electron escape from self-organized InAs quantum dots ͑QD's͒ in a vertical electric field by time-resolved capacitance spectroscopy. Direct tunneling and a thermally activated escape process are observed. The QD electron ground and first-excited states are concluded to be located ϳ190 and ϳ96 meV below the GaAs matrix conduction band, respectively. Our experimental results and their interpretation are in good agreement with eight-band k•p calculations and demonstrate the importance of tunnel processes.

The electronic properties of self-organized GaSb quantum dots (QDs) embedded in GaAs n+p diodes were investigated by capacitance–voltage and deep level transient spectroscopy. The localization energy of the hole ground state is 450 meV. State filling lowers the activation energy to 150 meV for completely charged QDs containing 15 holes. The hole retention time at room temperature for a single hole per QD is extrapolated to be in the microsecond range, about five orders of magnitude longer than in In(Ga)As/GaAs QDs. Hence, we consider GaSb/GaAs to be a suitable material system for future QD memory applications which require long storage times.

Carrier escape processes from self-organized InAs quantum dots QDs embedded in GaAs are investigated by time-resolved capacitance spectroscopy. Electron emission is found to be dominated by tunneling processes. In addition to tunneling from the ground state, we find thermally activated tunneling involving excited QD states with an activation energy of 82 meV. For holes, the tunnel contribution is negligible and thermal activation from the QD ground state to the GaAs valence band with an activation energy of 164 meV dominates. Extrapolation to room temperature yields an emission time constant of 5 ps for holes, which is an order of magnitude larger than for electrons. The measured activation energies agree well with theoretically predicted QD levels.

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 observation of tunneling emission of electrons and holes from In͑Ga͒As/ GaAs quantum dots in timeresolved capacitance measurements is reported. The electron and hole ground-state localization energies are determined as ͑290± 30͒ meV and ͑210± 20͒ meV, respectively. These energies are in excellent agreement with predictions from eight-band k · p theory. Based on the localization energies, we estimate the escape time for thermal excitation at room temperature as ϳ200 ns for electrons and ϳ0.5 ns for holes in case of a zero-electric-field situation. The electric-field dependence of the tunneling emission is investigated in detail.