Adsorption of Indium on an InAs wetting layer deposited on the GaAs(001) surface

n this work, we perform a first-principles study of the adsorption properties of an In adatom deposited on a 1.75 ML( monolayer) InAs, forming a wetting layer on GaAs(001) with the alpha2(2×4) or beta2(2×4) reconstruction. Thus, we are addressing here the important case of the wetting layer at a high In coverage, just before the occurrence of the two-dimensional to three-dimensional transition. The structural properties of these reconstructions have been studied: we determine the equilibrium geometry of the surfaces and their stability for various growth conditions. We have then carried out a detailed study of the potential energy surface (PES) for an In adsorbate, finding the minima and the saddle points. The main characteristics of the PES and the bonding configurations of the In adatom on the surface are analyzed by comparing them with analogous studies reported in the literature, trying to extract the effects due to (i) the compressive strain to which the InAs adlayer is subjected, (ii) the particular surface reconstruction, and (iii) the wetting layer composition. We found that, in general, stable adsorption sites are located at (i) locations beside the As in-dimers, (ii) positions bridging two As in-dimers, (iii) between two adjacent ad-dimers (only in beta2), and (iv) locations bridging two As ad-dimers. We find also other shallower adsorption sites which are more reconstruction specific due to the lower symmetry of the alpha2 reconstruction compared to the beta2 reconstruction. We point out that the alpha2 reconstruction has the lowest symmetry among the reconstructions studied so far for this system.