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, {3O(i)}, triple oxygen with a nitrogen atom, {Ni, 3O(i)}, triple nitrogen with an oxygen atom, {3N(i), O-i}, double hydrogen and an oxygen atom, {2H(i), O-i}, double hydrogen and oxygen atoms, {2H(i), 2O(i)} and four hydrogen/nitrogen/oxygen complexes, {H-i, N-i, O-i}, {2H(i), N-i, O-i}, {H-i, 2N(i), O-i}, and {H-i, N-i, 2O(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, 2O(i)} and {3O(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.