A backside illuminated image sensor includes a semiconductor layer having a back-side surface and a front-side surface. The semiconductor layer includes a pixel array region including a plurality of photodiodes configured to receive image light through the back-side surface of the semiconductor layer. The semiconductor layer also includes a peripheral circuit region including peripheral circuit elements for operating the plurality of photodiodes that borders the pixel array region. The peripheral circuit elements emit photons. The peripheral circuit region also includes a doped semiconductor region positioned to absorb the photons emitted by the peripheral circuit elements to prevent the plurality of photodiodes from receiving the photons.