Island shape instabilities and surfactant-like effects in the growth of InGaAs/GaAs quantum dots

InGaAs/GaAs island formation during vapor phase epitaxy showed diverging be haviors when varying group V partial pressures (PP). Differences include ch anges in critical thicknesses for the onset of the Stranski-Krastanow (S-K) transformation, surface coverages, ratios between coherent and incoherent islands, and dissimilar morphologies upon annealing. These results show tha t slightly different values for the 2D-3D transition can also be obtained i n InGaAs/GaAs depending on AsH3 PP. Photoluminescence spectroscopy of cappe d islands showed that the wetting layer thickness does not change beyond th e onset of the S-K transformation for conditions producing stable islands. Annealing experiments done at high AsH3 PP show Ostwald ripening, but we al so observe that small, high density, lens-shaped islands are unaffected by prolonged annealing and do not ripen when an 'optimum' low AsH3 PP is used during the island growth and in-situ annealing. The later experiments show that small lens shaped islands can be found in equilibrium if InGaAs surfac e energies are minimized. These findings lead to the conclusion that AsH3 c an raise surface energies acting as an impurity-free 'morphactant' in InGaA s growth. (C) Published by 1999 Elsevier Science S.A. All rights reserved.