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

Abstract

InGaAs/GaAs island formation during vapor phase epitaxy showed diverging behaviors when varying group V partial pressures (PP). Differences include changes 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 that slightly different values for the 2D–3D transition can also be obtained in InGaAs/GaAs depending on AsH 3 PP. Photoluminescence spectroscopy of capped islands showed that the wetting layer thickness does not change beyond the onset of the S–K transformation for conditions producing stable islands. Annealing experiments done at high AsH 3 PP show Ostwald ripening, but we also observe that small, high density, lens-shaped islands are unaffected by prolonged annealing and do not ripen when an ‘optimum’ low AsH 3 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 surface energies are minimized. These findings lead to the conclusion that AsH 3 can raise surface energies acting as an impurity-free ‘morphactant’ in InGaAs growth.