The present invention provides silicon based thin-film structures that can be used to form high frequency optical modulators. Devices of the invention are formed as layered structures that have a thin-film dielectric layer, such as silicon dioxide, sandwiched between silicon layers. In one aspect of the invention an electrical contact structure is provided. The electrical contact structure comprises a connecting portion that electrically connects an active region of at least one of the silicon layers to a contact portion of the electrical contact structure.