Virtual-surfactant mediated epitaxy of InAs on GaAs(001) studied by scanning tunneling microscopy

The mechanism of virtual-surfactant mediated molecular beam epitaxy (MBE) of InAs on GaAs(001) was investigated by in situ scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). InAs layers with thicknesses ranging from 1 to 20 monolayers (ML) do not exhibit any strain driven morphological phase transition when grown under In-rich conditions. RHEED and STM confirm a well-ordered (4 x 2) reconstruction of these In-terminated surfaces. Three different atomic structure models that agree with the STM images are discussed. Large STM scans reveal a characteristic morphology of rectangularly shaped islands and step edges with a large degree of anisotropy. We attribute these new findings to a special strain reducing growth mode that is related to the In-rich (4 x 2) surface reconstruction.