Generation of second harmonics in Ge-doped SiO2 thin films by ultraviolet irradiation under poling electric field

Thin films of Ge-doped silica were prepared by radio-frequency sputtering in a controlled atmosphere of Ar and O-2 and then subjected to ultraviolet irradiation under poling electric field (UV poling). Effects of oxygen mass flow content during the sputtering on the second-order nonlinearity of the films were investigated. Second harmonic generation (SHG) was observed and its intensity was found to depend greatly on the oxygen mass flow content with an optimum at 1 cm(3)/min. The annealing in a vacuum enhanced SHG intensity and values as high as 12.5 +/- 0.6 pm/V have been achieved with films containing 50 mole % of GeO2. This is on one hand, and we also found that loading thin films with hydrogen prior to UV poling largely improved the decay of SHG. A decay time as long as 7 years has been obtained. The change in second-order optical nonlinear properties of the films is discussed based on structural defects. (C) 2000 American Institute of Physics. [S0021-8979(00)01705-9].