Electro optical absorption in hydrogenated amorphous silicon (a-Si: H)-amorphous silicon carbonitride (a-SiC, Ny) multilayers have been studied in two different planar multistack 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 X= 1.55\ua through the application of an electric field which induces free carrier accumulation across the multiple insulator/semiconductor device structure.