Structural transformations and strain relaxation mechanisms of In_0.6Ga_0.4As islands grown by molecular beam epitaxy on GaAs(001) substrates

The shape transformations and the mechanism of misfit strain relaxation of In_0.6Ga_0.4As islands grown at different temperatures on GaAs(001) substrates have been investigated. Layers with a constant nominal thickness of 12 monolayers were deposited by molecular beam epitaxy on nominal singular and on vicinal substrates. The specimens were characterized by scanning electron microscopy, transmission electron microscopy and high‐resolution transmission electron microscopy. It is shown that an increase of the growth temperature yields a shape transition from rounded islands to elongated cigar‐like structures. The lattice‐parameter mismatch in the circular islands is relaxed by misfit dislocations at lower growth temperatures. Indium desorption effectively reduces the mismatch at higher growth temperatures and therefore yields the nucleation of coherent islands. In spite of this structural transformation an Arrhenius‐like behaviour of the island densities is observed with an activation energy which depends on the substrate tilt.