Silicon photodetectors with triple p-n junctions in CMOS technology at 650-and 850-nm wavelengths

A triple p-n junction Si photodetector using 0.25-μm standard CMOS process at 650-and 850-nm wavelengths is presented and investigated. Triple p-n junctions are formed vertically by n⁺-implant/p-well (N+/HVPW), p-well/n+-buried layer (HVPW/NBL), and n⁺-buried layer/p-substrate (NBL/P-sub) junctions to attain a wavelength-dependent response. The responsivity and pulse response were characterised in different bias schemes. Measured photocurrents from HVPW/NBL and NBL/P-sub junctions under reverse biasing and a floating electrode on N⁺-HVPW showed the smallest FWHM values. The.3 dB bandwidth of 1.9 GHz converted from pulse measurement is the highest result ever reported in 654-nm wavelength using standard CMOS technology. The proposed triple p-n junction Si photodetector with bias schemes shows combined excellent performance in 650-and 850-nm wavelengths.