Solid-state imaging device and method of detecting optical signals using the same

A solid-state imaging device equipped with a plurality of unit pixels each including a photo-diode and an insulated gate field effect transistor, said photo-diode comprising:

• a substrate having a first conductivity type;
• a semiconductor layer formed on said substrate and having a second conductivity type;
• a well region formed on said semiconductor layer and having the first conductivity type;
• an impurity region formed on the surface of said well region and having the second conductivity type, and
• said insulated gate field effect transistor comprises:
• a drain region formed on the surface of said well region, extending to said impurity region, and having the second conductivity type;
• a source region formed on the surface of said well region, spaced apart from said drain region, and having the second conductivity type;
• a gate electrode formed on a gate insulation layer which is formed on a gate region being said well region between said drain region and said source region;
• and
• a heavily doped buried layer formed in said well region near said source region below said gate electrode, said heavily doped buried layer doped with an impurity of the first conductivity type heavier in concentration than said well region.