Spectrally resolved photoresistance investigations of charge storage effects in self-assembled InAs quantum dots (QDs) are reported. Resonant optical excitation of the QDs produces a strong increase of the lateral resistance of a spatially separated electron channel (ΔR) which reflects the stored charge density. This photoresponse is persistent for many hours at 145 K and can be controllably reversed electrically. Pronounced oscillations observed in the spectral variation ΔR are shown to reflect the excitation spectrum of the QD ensemble showing resonances that arise from both direct and phonon-assisted absorption processes.

We have investigated the influence of various growth parameters on the optical properties of self-assembled InAs/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) in Stranski–Krastanov mode. Metastably sized QDs have been observed in photoluminescence measurements, which are fabricated by depositing 2.5 monolayers (ML) InAs at a substrate temperature of 530 °C and As4 pressure of (1.6±0.2)×10−5 mbar. These self-assembled QDs exhibit both good optical quality and a narrow size distribution with a full width at half maximum of ∼35 meV both at room temperature and at 4.2 K. By investigating the dependence of the optical properties on the substrate temperature and arsenic pressure, we show that the diffusion length of the adatoms is responsible for changes in size, density, and quantum efficiency of the QDs beside the amount of InAs deposited. The growth conditions for fabricating QDs are optimized for substrate temperatures Ts=480 and 530 °C. A high QD density (∼1×1011 cm−2) with a broad size distribution and a lower QD density (∼1.2×1010 cm−2) with a narrow size distribution, which are determined by atomic force microscopy have been obtained by MBE growth at Ts=480 and 530 °C, respectively. Stacking several QD layers separated by thin GaAs spacers in order to achieve a higher QD density improves the optical properties of the islands. The thermal stability of the QDs has been tested by annealing the samples at high temperatures in order to determine the highest possible substrate temperature for the following expitaxial layers. The QDs grown at 530 °C can be overgrown at 700–720 °C, while the QDs grown at 480 °C can only be overgrown at 600–620 °C without obvious decrease of the quantum efficiency of the QDs.