Amorphous Silicon Photodetectors for Silicon Based Optical Waveguides

In this work performances of amorphous silicon photodetectors used to sense the light guided in Oxidised Porous Silicon Waveguides (OPSWG) are presented. We have developed an original technology to fabricate silicon oxide channel waveguides on monocrystalline silicon wafers, consisting of selective anodization followed by thermal process. Due to the peculiar fabrication process waveguides are placed just under the surface of the silicon wafer. a-Si:H film has been grown on the top of the waveguide by a low temperature (PECVD) process, then aluminum contacts have been formed by standard lithography. Because of the higher a-Si:H refractive index with respect to silicon oxide, the guided light is deviated in the film where a-Si:H substitutes the top air cladding. The high a-Si:H absorption coefficient in the visible range permits the efficient detection of guided light and conversion into an electrical signal. In this paper different devices structures and coupling geometries between waveguide and detector are presented. I/V characteristics in the dark and under light excitation have been used to extrapolate equivalent electrical models, also reported in the paper. The obtained results showed that the system OPSWG/a-Si:H sensor is suitable for optoelectronic applications.