Addressable photosensing elements for 2-dimensional image sensors using a-Si alloy p-i-n diodes

We describe amorphous silicon alloy addressable photo-sensitive elements whose operation has been experimentally verified in 2-dimensional image sensors. The investigated structures consist of p-i-n photodiodes (PD) stacked and back-to-back connected to n-i-p blocking diodes (BD). A first developed device is based on a TCO -p+(Si)-i(Si)-n+(Si)-i(SiC)-p+(SiC)-Metal structure. Due to an optimization of the thickness and of the energy gap of the layers, we obtained a rectification ratio between the current levels in forward and reverse bias conditions If/Ir ≈104, under AM1.5 illumination, filtered at 500 nm. A better rectification ratio If/Ir>106, under white AM1.5 light, has been achieved by introducing a metallic film inside the n+ layer, for light shielding; this further technological step allows both the independent optimization of BD's and PD's structures, and the increase of the operation speed.