Electronegativity and doping in Si1-xGex alloys

Silicon germanium alloys are technologically important in microelectronics but also they are an important paradigm and model system to study the intricacies of the defect processes on random alloys. The key in semiconductors is that dopants and defects can tune their electronic properties and although their impact is well established in elemental semiconductors such as silicon they are not well characterized in random semiconductor alloys such as silicon germanium. In particular the impact of electronegativity of the local environment on the electronic properties of the dopant atom needs to be clarified. Here we employ density functional theory in conjunction with special quasirandom structures model to show that the Bader charge of the dopant atoms is strongly dependent upon the nearest neighbor environment. This in turn implies that the dopants will behave differently is silicon-rich and germanium-rich regions of the silicon germanium alloy

Impact of local composition on the energetics of E-centres in Si1−xGex alloys

The energetics of the defect chemistry and processes in semiconducting alloys is both technologically and theoretically significant. This is because defects in semiconductors are critical to tune their electronic properties. These processes are less well understood in random semiconductor alloys such as silicon germanium as compared to elementary semiconductors (for example silicon). To model the random silicon germanium alloy we have employed density functional theory calculations in conjunction with the special quasirandom structures model for different compositions. Here we show that, the energetics of substitutional phosphorous-vacancy pairs (Ecentres) in Si1-xGex alloys vary greatly with respect to the local Ge concentration and the composition of the alloy. The most energetically favourable E-centres have a Ge atom as a nearest neighbour, whereas the dependence of the binding energy of the Ecentres with respect to alloy composition is non-linear

Using the Bond Valence Sum Model to calculate Li-diffusion pathways in Silicene with MgX2 (X=Cl, Br, I) substrates

Using the BVS method, we calculate Li-ion pathways and diffusion barriers in the interface between silicene and MgCl2, MgBr2 and MgI2 substrates and we show that the results are in good agreement with the previously published DFT studies. In addition, we showcase that BVS does not need the exact crystal structure as we examine different initial positions for the Li ion and different interface heights without affecting the calculated BVSE. Furthermore, we show that surface diffusion BVS calculations can be used to roughly optimize the interface, thus completely foregoing DFT geometry optimization calculations. Here, we propose that BVS can substitute DFT as a quick filter when searching for low migration barriers in silicene-based materials, providing good enough accuracy