A back-illuminated image sensor (500) includes a sensor layer (606) disposed between an insulating layer (604) and a circuit layer electrically connected to the sensor layer. An imaging area includes a plurality of photodetectors (616) formed in the sensor layer and a well (800) 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 including a region 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 (704) between the sensor layer and the insulating layer.