This paper reports the design, fabrication and characterization of a planar waveguide based on an hydrogenated amorphous silicon (a-Si: H)–silicon carbonitride (SiCxNy) multistack for the realization of passive and active optical components at the wavelength 1.3-1.5 μm. The waveguide was realized by low temperature plasma enhanced chemical vapour deposition (PECVD) compatible with standard microelectronic technologies. Electro-optical modulation at λ= 1.5 μm is demonstrated in this waveguide. The device operates by varying the free carrier concentration to change the Si absorption coefficient in the guiding region. It has been modelled using the two-dimensional (2-D) device simulation package SILVACO and the optical simulator Beam PROP to determine its electrical and optical performances, respectively.