The present disclosure, in some embodiments, relates to an integrated chip. The integrated chip has a photodetector region arranged within a semiconductor substrate. One or more dielectric materials are disposed within a trench defined by one or more interior surfaces of the semiconductor substrate. A doped epitaxial material is arranged within the trench and is laterally between the one or more dielectric materials and the photodetector region. A dielectric protection layer is arranged over the one or more dielectric materials within the trench. The dielectric protection layer laterally contacts a sidewall of the doped epitaxial material.