Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)

We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the ${\mathrm{As}}_2$ adsorption-desorption process and by the lowering of the In binding energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.