A back-illuminated image sensor includes a sensor layer disposed between an insulating layer and a circuit layer electrically connected to the sensor layer. An imaging area includes a plurality of photodetectors is formed in the sensor layer and a well that spans the imaging area. The well can be disposed between the backside of the sensor layer and the photodetectors, or the well can be a buried well formed adjacent to the backside of the sensor layer with a region including formed between the photodetectors and the buried well. One or more side wells can be formed laterally adjacent to each photodetector. The dopant in the well has a segregation coefficient that causes the dopant to accumulate on the sensor layer side of an interface between the sensor layer and the insulating layer.