Droplet epitaxy of InGaAs quantum dots on (100) GaAs substrate

In 1991 N. Koguchi et al. has proposed an alternative growth technique named droplet epitaxy (DE) for fabrication of self-organized nanostructures. DE offers the fabrication of nanostructures with reduced or without wetting layer on both lattice matched and lattice-mismatched substrates in comparison to the widely used Stranski-Krastanov (SK) growth mode, which is extremely attractive for the growth of lattice-mismatched substrates. Many groups use low temperature QD DE growth to prevent material redistribution. But the low temperature results in poor crystal quality of the QD structures, which needs additional annealing steps at high temperatures. We report on the structural (atomic force microscope) and optical (macro- and micro-photoluminescence) properties of InGaAs QDs grown by DE on undoped (100)GaAs substrates at elevated growth temperatures in the range from 410 C to 500 C to preserve the crystal quality of QDs. By using different growth conditions such as substrate temperature, amount and deposition rate of In, As flux and the opening time of the As valve, QDs with small sizes (height: 2-6 nm) and narrow photoluminescence linewidth (30 meV) are fabricated. Sharp and intense luminescence lines obtained by micro-photoluminescence spectroscopy showed good quality of QDs formed by DE.