Electron beam poling in amorphous Ge-doped H:SiO2 films

Amorphous Ge-doped H:SiO2 films on silica, deposited by matrix-distributed electron cyclotron resonance – plasma enhanced chemical vapor deposition, were irradiated with an electron beam while varying the dose. Using the Maker fringe method, second-harmonic generation was measured in the irradiated regions of the films. With a current of 5 nA, and an acceleration voltage of 25 kV for 25 s, a Ge-doped H:SiO2 film (3.8 at.% Ge) showed a maximum second-order nonlinearity of d33 = 0.0005 pm/V. In contrast, a H:SiO2 film with a smaller Ge content (1.0 at.% Ge), showed a large SHG: d33 = 0.06 pm/V when irradiated for 15 s. The second-harmonic generation in the films is caused by a frozen-in electric field induced by charge implantation from the electron beam. The strength of the electric field is determined by two conditions: the trapping centers (numbers, depth) and the remaining conductivity under large electric field.