Electro optical absorption in hydrogenated amorphous silicon (α-Si:H) ??? amorphous silicon carbonitride (α-SiCxN_y) multilayers have been studied in two different planar multistacks waveguides. The waveguides were realized by plasma enhanced chemical vapour deposition (PECVD), a technology compatible with the standard microelectronic processes. Light absorption is induced at λ = 1.55 μm through the application of an electric field which induces free carrier accumulation across the multiple insulator/semiconductor device structure. The experimental performances have been compared to those obtained through calculations using combined twodimensional (2-D) optical and electrical simulations.