Control of size and density of InAs/(Al, Ga)As self-organized islands

We report on the influence of the chemical composition of the (Al, Ga)As surface on the formation of strain induced three-dimensional (3D) InAs islands. The experiments have been carried out using a molecular beam epitaxy facility combined with a scanning tunneling microscope enabling in situ surface characterization. The evolution of the density and morphology of these islands is investigated as a function of the Al composition. The InAs deposition, substrate temperature, and annealing time effects on the island formation and morphology are studied. The morphologies of the (Al, Ga)As surface as well as that of the reconstructed InAs "wetting layer" are also described. Results indicate that there are major differences between the InAs/GaAs and the InAs/AlAs systems despite the same lattice mismatch. We observe these differences varying the aluminum content in the starting (Al, Ga)As surface. We show that control of the Al fraction leads to control of the size and density of the 3D islands. The control of island density and size as well as the growth mode of these islands is explained by considering the difference in surface mobility and cation intermixing between these two systems. Our observation is that strain energy is not the only parameter governing the formation of 3D islands but the chemical nature of the different layers involved is proved to significantly affect island properties. (C) 2001 American Institute of Physics.