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.