On the location of InAs quantum dots on GaAs(0 0 1)

Thin layers of InAs were deposited onto GaAs(0 0 1) substrates using molecular-beam epitaxy. The transition from the two-dimensional wetting layer to three-dimensional quantum dots (QDs) of strained InAs was studied by in situ scanning tunneling microscopy with atomic resolution. Closely before the transition, the wetting layer exhibits a flat morphology with mostly straight and parallel steps. The transition occurs during a coverage increase by less than 0.2 ML only. After the transition the wetting layer shows step meandering and holes. Besides the continuously deposited InAs material from the molecular beams, mass transport from the wetting layer and even out of the substrate is concluded to contribute to QD formation. The location of the QDs with respect to the step edges is discussed within a model.