Wetting layer evolution in InAs/GaAs(001) heteroepitaxy: effects of surface reconstruction and strain

InAs heteroepitaxy on the (2 x 4) and c(4 x 4) reconstructed surfaces of GaAs(0 0 1) has been studied using scanning tunnelling microscopy, with particular emphasis on the formation and evolution of the two-dimensional (2D)InxGa1-xAs wetting layer. The influence of the initial GaAs reconstruction on the growth behaviour is significant for InAs coverages (theta) < 0.8 ML, but both qualitative (surface morphology and reconstruction) and quantitative (step density) surface characteristics converge for theta > I ML. The effects of surface reconstruction are only important for sub-ML InAs coverages, with strain effects dominating at higher coverages. STM topographs indicate a high and rapid disordering of the WL for theta > 0.5 ML, implying that strain-driven alloyed WL formation is important even below theta = I ML. The 2D --> 3D growth mode transition and the formation of self-assembled quantum dots (QDs) is delayed at low As fluxes. In this case strain relief occurs first by a reconstruction change from (I x 3) to a more In-rich (4 x 2) structure, with QD formation taking place only after the deposition of an additional amount of InAs (similar to0.2 ML). (C) 2002 Elsevier Science B.V. All rights reserved.