It is presented in this paper a study on the photo‐electronic properties of multilayer a‐Si:H/a‐SiC:H p–i–n–i–p structures. This study is aimed to give an insight into the internal electrical characteristics of such a structure in thermal equilibrium, under applied bias and under different illumination condition. Taking advantage of this insight it is possible to establish a relation among the electrical behavior of the structure, the structure geometry (i.e. thickness of the light absorbing intrinsic layers and of the internal n‐layer) and the composition of the layers (i.e. optical bandgap controlled through percentage of carbon dilution in the a‐Si1–x Cx:H layers). Showing an optical gain for low incident light power con‐ trollable by means of externally applied bias or structure composition, these structures are quite attractive for photo‐sensing device applications, like color sensors and large area color image detector. An analysis based on numerical ASCA simulations is presented for describing the behavior of different configurations of the device and compared with experimental measurements (spectral response and current–voltage characteristic). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)