Influence of growth conditions on the photoluminescence of self-assembled InAs/GaAs quantum dots

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 ${\mathrm{As}}_{\mathrm{4}}$ pressure of ${\text{(1.6±0.2)×10}}^{\text{−5}}\hspace{0.17em}\mathrm{mbar}.$ 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 $T_s\text{=480}$ and 530 °C. A high QD density ${\text{(∼1×10}}^{11}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-2}})$ with a broad size distribution and a lower QD density ${\text{(∼1.2×10}}^{10}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-2}})$ with a narrow size distribution, which are determined by atomic force microscopy have been obtained by MBE growth at $T_s\text{=480}$ 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.