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, {N_i,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.