The nitrogen-vacancy defect in Si1-xGex

Defect processes and energetics in semiconducting alloys is scientifically and technologically important as silicon germanium (Si_{1 - x}Ge_x) is a mainstream nanoelectronic material. It is established that point defects and defect clusters have an increasing role in the physical properties of Si_{1 - x}Ge_x particularly with the ever-decreasing critical dimensions of nanoelectronic devices. Nitrogen-vacancy defects in Si_{1 - x}Ge_x are bound and have the potential to change the optical and electronic properties and thus need to be investigated as absolute control is required in nanoelectronic devices. The nitrogen-vacancy defects are not extensively studied in Si_{1 - x}Ge_x random semiconductor alloys. Here we employ density functional theory (DFT) in conjunction with the special quasirandom structures (SQS) method to calculate the binding energies of substitutional nitrogen-vacancy pairs (NV) in Si_{1 - x}Ge_x alloys. This is a non-trivial problem as the energetics of these defect pairs are dependent upon the nearest neighbour Ge concentration and the composition of Si_{1 - x}Ge_x. The criterion for NV stability is binding energy and here it is shown that the most bound NV defects will form in high Si-content Si_{1 - x}Ge_x alloys.