A photosensitive detection unit has a composite dielectric gate MOS-C portion and a composite dielectric gate MOSFET portion. The two portions are formed above a same P-type semiconductor substrate, and share a charge coupled layer. A plurality of the photosensitive detection units are arranged on a same P-type semiconductor substrate in form of an array to obtain a detector. Adjacent unit pixels in the detector are isolated by deep trench isolation regions and P+-type injection regions below the isolation regions. During the detection, the P-type semiconductor substrate in the composite dielectric gate MOS-C portion senses light and then couples photoelectrons to the charge coupled layer, and photoelectronic signals are read by the composite dielectric gate MOSFET portion.