1. A MOS or CMOS based active sensor array comprising: 1) a substrate, 2) a plurality of MOS or CMOS pixel circuits fabricated in or on said substrate, each pixel circuit comprising: 1) a charge collecting electrode for collecting electrical charges and 2) plurality of transistors for monitoring periodically charges collected by said charge collecting electrode, 3) a photodiode layer of charge generating material located above said pixel circuits for converting electromagnetic radiation into electrical charges, said photodiode layer comprising an N-doped layer, a P-doped layer and an intrinsic layer in between said P-doped layer and said N-doped layer, wherein one of said N-doped layer or said P-doped layer defines a bottom photodiode layer, is in electrical contact with said charge collecting electrode and is configured to avoid any significant pixel to pixel crosstalk, 4) a surface electrode in the form of a thin transparent layer or grid located above said layer of charge generating material; and 5) a micro-lens array for focusing light of above said charge collecting electrodes and away from pixel edges; wherein electrical charges generated in regions of said photodiode layer above a particular charge collecting electrode are collected by that particular charge collecting electrode and no substantial portion of said of the electrical charges generated above that particular charge collecting electrode are collected by any other charge collecting electrode.