The effect of defects on the optical nonlinearity of thermally poled SiO_x thin films

Defects were deliberately induced in SiO_x thin films during their deposition using a helicon plasma activated reactive evaporation technique. The films were thermally poled and the poling induced second-order optical nonlinearity was investigated by measuring the second harmonic generation of the samples. It was found that oxygen-rich SiO_x thin films containing mainly peroxy radicals enabled a much larger optical nonlinearity than stoichiometric SiO₂ films after poling, and their optical nonlinearity was long-time stable; while silicon-rich SiO_x thin films containing mainly oxygen vacancy defects presented a smaller and unstable optical nonlinearity after poling.