An integrated circuit device for converting an incident optical signal into an electrical signal comprises a semiconductor substrate, a well region formed inside the semiconductor substrate, a dielectric layer formed over the well region, and a layer of polysilicon for receiving the incident optical signal, formed over the dielectric layer, including a p-type portion, an n-type portion and an undoped portion disposed between the p-type and n-type portions, wherein the well region is biased to control the layer of polysilicon for providing the electrical signal.