Image sensors with small pixels having high well capacity

An image sensor having an array of image sensor pixels and a silicon substrate, the image sensor comprising:

• a plurality of photodiodes formed in a surface of the silicon substrate, wherein the silicon substrate includes a bulk portion under the plurality of photodiodes;
• a p+ type doped layer that extends under the plurality of photodiodes parallel to the surface, wherein the p+ type doped layer comprises a plurality of openings through which charge carriers pass from the bulk portion of the silicon substrate he photodiodes;
• and
• a plurality of compensating n-type doped implant regions, wherein each compensating n-type doped implant region is formed in a respective one of the openings.

A system, comprising:

• a central processing unit;
• memory;
• input-output circuitry;
• and
• an image sensor pixel in a pixel array having a silicon substrate, comprising:
• a photodiode thrilled in a surface of the silicon substrate, wherein the silicon substrate includes a bulk portion under the photodiode;
• a p+ type doped layer that extends under the photodiode parallel to the surface, wherein the p+ type doped layer comprises an opening through which charge carriers pass from the bulk portion of the silicon substrate to the photodiode;
• and
• a compensating n-type doped implant region in the opening.