In adatom diffusion on InxGa1-xAs/GaAs(001): effects of strain, reconstruction and composition

By using density functional theory (DFT) calculations of the potential energy surface in conjunction with the analytical solution of the master equation for the time evolution of the adatom site distribution, we study the diffusion properties of an isolated In adatom on InxGa1-xAs wetting layers (WL) deposited on the GaAs(001). The WL reconstructions considered in this study are, listed in the order of increasing In coverage: c(4 x 4), (1 x 3), (2 x 3), alpha(2)(2 x 4) and beta(2)(2 x 4). We analyze the dependence of the diffusion properties on WL reconstruction, composition and strain, and find that: (i) diffusion on the (2 x N) reconstructions is strongly anisotropic, owing to the presence of the low barrier potential in-dimer trench, favoring the diffusion along the [(1) over bar 10] direction over that along the [110] direction; (ii) In diffusion at a WL coverage theta = 2/3 monolayers (ML; with composition x = 2/3) is faster than on clean GaAs(001) c(4 x 4), and decreases at theta = 1.75 ML (x = 1; e. g. InAs/GaAs(001)); (iii) diffusion and nucleation on the (2 x 4) WL is affected by the presence of adsorption sites for indium inside the As dimers; (iv) the approximation used for the exchange-correlation potential within DFT has an important effect on the description of the diffusion properties.