Broad Spectral Response of PD in FSI-CIS With Near-IR Sensitivity Enhancement Based on the Model of Full Impurity Compensation

Traditional CMOS image sensors (CISs) mainly work in the visible light range of 400–700 nm, but the narrow spectral response range limits their application. According to the structure and light absorption characteristics of the photodiode (PD) in a front-side illuminated (FSI) CIS, a novel PD with impurity compensation (PDc) is designed, namely, the p-n junction of a PD is replaced by the same thickness (assuming $0.6~\mu $ m) of impurity compensation region (expressed as PDNc). A study shows that if the PDNc replacing the p-n in PD is the case of full impurity compensation (i.e., PD $\to $ PDfc), a quantum efficiency (QE) peak value can be improved from 0.86 of PD to 0.93 of PDfc, with spectral response range broadened from visible to near-infrared region. The improvement of above properties is related to the localized state levels formed by impurity compensation. If the PDNc replacing the p-n in PD is the case of near full impurity compensation (i.e., PD $\to $ PDnfc), the QE-peak value of PDnfc is slightly lower than that of PDfc in the wide spectral range of 400–2000 nm. The technology computer-aided design (TCAD) simulation indicates that the design of a new pixel with PDc for a CIS is feasible in terms of process.