Nonlinear optical properties of SiO2 layers

Nonlinear optical properties of SiO₂ layers are very interesting for applications in integrated electro-optical devices. Previous experiments, mostly performed on multilayer structures, show that nonlinear optical effects exist in SiO₂ layers after application of a high electric field. In the present experiment a single layer of SiO₂ was prepared by thermal oxidation of a silicon substrate. A transparent electrode was deposited on the top of the layer. Electron-beam charging was used to generate the nonlinear optical effects. A reflection technique which utilizes the propagation of a polarized laser beam through the ac biased sample was used for measuring the electro-optical coefficient: due to the electro-optical effect in the investigated SiO₂ layer, the plane of polarization of the beam, which is partially reflected at the Si-SiO₂ interface, oscillates compared to the polarization of the input laser beam. The observed electro-optical coefficient r₃₃ is approximately 1.5 pm/V at λ=780 nm and is higher than previously measured coefficients in SiO₂. The effect shows no decay at room temperature over a period of several days