Solid-state imaging device with improved photodetector

A solid-state imaging device comprising:

• a photodetector comprising a substrate, a first conductivity type semiconductor layer disposed on said substrate, a second conductivity type semiconductor region disposed in said layer having a dopant impurity concentration varying with position within said region relative to said substrate, a first conductivity type region disposed in said second conductivity type semiconductor region, and a second conductivity type semiconductor subregion disposed between and contacting said first conductivity type region and said second conductivity type region and forming a same conductivity type junction with said second conductivity type region, said second conductivity type subregion having a dopant impurity concentration varying with position within said second conductivity type subregion relative to said substrate and wherein the dopant impurity concentration in said second conductivity type subregion adjacent the same conductivity type junction is higher than the dopant impurity concentration in said second conductivity type region adjacent the same conductivity type junction and a net dopant impurity concentration profile of said second conductivity type subregion and said second conductivity type region includes an inflection point at the same conductivity type junction of said second conductivity type subregion and said second conductivity type region whereby signal charges produced in response to incident light are stored in said second conductivity type subregion of said photodetector for being read out as a light signal.