Segregation effects at vacancies in AlxGa1-xN and SixGe1-x alloys

It is shown by quantum molecular-dynamics calculations that the formation energies of vacancies in semiconductor alloys strongly depend on the chemical identities of their nearest-neighbor atoms. For example, in AlxGa1-xN alloys the Ga-terminated vacancy is lower in energy than the Al-terminated one by 2.8 eV, while the corresponding difference in SixGe1-x is 1 eV. This leads to unexpectedly strong preferences for vacancy termination in semiconductor alloys: The results also predict that local segregation will occur at grain boundaries and dislocations. [S0163-1829(99)03103-3].