In this paper, a high sensitivity photosensor is proposed that utilizes the Zinc Oxide (metallic ZnO) which act as a transparent optical window over channel. High sensitivity is achieved by using Cylindrical Surrounding Gate Metal Oxide Semiconductor Field Effect Transistor (CSG MOSFET). On being exposed to light there is substantial increase in conductance and thereby change in the subthreshold current under exposure is utilized as a sensitivity parameter. Most of the Conventional FET based photosensors that are available utilizes threshold voltage as the parameter for sensitivity comparison but in this proposed sensor, under illumination change in the conductance resulting in variation of the subthreshold current is considered to be the sensitivity parameter. Performance comparison with Double Gate Metal Oxide Semiconductor Field Effect Transistor (DG MOSFET) in terms of sensitivity, threshold voltage and Ion/Ioff ratio is also done and observed results shows that CSG MOSFET is an ideal candidate for being used as a high sensitivity photosensor because in CSG MOSFET due to effective control of gate over channel low dark current, high sensitivity, low threshold voltage and high Ion/Ioff ratio can be achieved. Further impact of channel radius on responsivity (Re), quantum efficiency (Qe) and Ion/Ioff ratio is also studied for the proposed device
