Hydrogen/nitrogen/oxygen defect complexes in silicon from computational searches

Point-defect complexes in crystalline silicon composed of hydrogen, nitrogen, and oxygen atoms are studied within density-functional theory. Ab initio random structure searching is used to find low-energy defect structures. We find new lowest-energy structures for several defects: the triple-oxygen defect, { 3 O_i }, triple oxygen with a nitrogen atom, { N _i, 3 O_i }, triple nitrogen with an oxygen atom, { 3 N _i, O_i }, double hydrogen and an oxygen atom, { 2 H _i, O_i }, double hydrogen and oxygen atoms, { 2 H _i, 2 O_i } and four hydrogen/nitrogen/oxygen complexes, { H_i, N_i, O_i }, { 2 H_i, N_i, O_i }, { H_i, 2 N_i, O_i }, and { H_i, N_i, 2 O_i }. We find that some defects form analogous structures when an oxygen atom is replaced by a NH group, for example, { H_i, N_i, 2 O_i } and { 3 O_i }, and { H_i, N_i } and { O_i }. We compare defect formation energies obtained using different oxygen chemical potentials and investigate the relative abundances of the defects.