Shape Transition of GaAs Islands Grown on InAs (001) Surfaces

We have observed the shape transition of three-dimensional (3D) GaAs islands grown on InAs (001) surfaces with increasing the GaAs deposition. A scanning tunneling microscopy image of a 1.0 monolayer (ML) GaAs-deposited on InAs surface showed 3D island formation with an island size of about 10 nm×20∼30 nm, extending in the [11̄0] direction. When 2.0 ML GaAs was deposited onto the InAs surface, this island shape changed to a compact, pyramid-like one. At this stage, smaller islands were formed on the InAs substrate surface, which was reconstructed to be an In-stabilized (4×2) structure. These islands coalesced and grew larger on the InAs substrate surface with increasing the amount of GaAs deposition.