Near-Infrared Sensitivity Enhancement of CMOS Image Sensor With Germanium On Silicon Structure

Silicon sensor has gained attention due to an increased demand for near-infrared CMOS image sensors for mobile imaging, digital cameras, industrial surveillance, and intelligent driving et.al. However, due to the low absorption rate of silicon for wavelength near 700 nm ~ 1100 nm, the silicon sensor has low detection efficiency which limits its application in near-infrared region. The detection efficiency represents the ability of an image sensor to convert photons into electrons and directly determines the image quality of image sensor. It is not only dependent on the wavelength, but also dependent on material. To increase the detection efficiency of the silicon sensor, germanium was widespread used because of the same lattice structure as silicon and higher optically responsive than silicon. In this paper, a new type of the image sensor with germanium integrated on silicon (Ge on Si) image sensor structure is presented and the detection efficiency of Ge on Si structure sensor was studied. It was demonstrated that the detection efficiency of Ge on Si structure sensor is 2.3 ~ 600 times higher than that of the silicon sensor for near-infrared wavelength of 700 nm ~ 1100 nm.