Electron-beam poling in undoped, N- or Ge-doped MDECR H:SiO2 films

Amorphous N- or Ge-doped H:SiO2 films deposited on silica by the matrix distributed electron cyclotron resonance-PECVD method were irradiated by an electron-beam with different doses in order to pole the material and induce second harmonic generation (SHG). SHG was measured using the Maker-fringe method. When irradiated at an acceleration voltage of 25 kV, an incident current of 5 nA during 480 s, the N-doped H:SiO2 films exhibited a maximum second harmonic signal in the order of 0.003 pm/V, but when irradiated with an acceleration voltage of 30 kV, at 5 nA during 240 s, the films exhibited a maximum second harmonic signal of 0.006 pm/V. With a smaller current of 0.5 nA during 25 s and 25 kV acceleration voltage, the Ge-doped H:SiO2 films (3.8 at. % Ge) showed a maximum second-order nonlinearity of 0.0005 pm/V. But an H:SiO2 films with a smaller Ge content (1.0 at. % Ge), showed a large SHG: d33=0.09 pm/V when irradiated at 25 kV, 0.5 nA during 15 s.