Keywords:submonolayer, AFM, quantum dots
We report topographical evidence of the 2D to 3D transition in InAs/GaAs nanostructures assembled by the submonolayer (SML) growth mode using molecular beam epitaxy (MBE). Whereas the 2D to 3D transition in InAs nanostructures assembled by the Stranski-Krastanov (SK) growth mode is well-established with a critical thickness of around 1.7 ML, the analogous phenomenon in SML-grown nanostructures is not yet well understood. In the present work, an atomic force microscopy (AFM) study is carried out to investigate the topographical changes associated with the 2D to 3D transition in SML nanostructures, and we demonstrate that there exists a critical thickness in the amount of InAs deposited per cycle, for a given number of stacks and GaAs matrix layer thickness, beyond which the abrupt nucleation of 3D nanostructures occurs. In addition, the results show that InAs/GaAs SML nanostructures exist in two distinct forms: 2D WL-like islands and 3D QD-like structures.