The present disclosure relates to an image sensor including a pixel along a substrate. The pixel includes a first semiconductor region having a first doping type. A second semiconductor region is directly over the first semiconductor region. The second semiconductor region has a second doping type opposite the first doping type and meets the first semiconductor region at a p-n junction. A ring-shaped third semiconductor region laterally surrounds the first and second semiconductor regions. The ring-shaped third semiconductor region has the first doping type. A ring-shaped fourth semiconductor region laterally surrounds the ring-shaped third semiconductor region. The ring-shaped fourth semiconductor region has the second doping type. A ring-shaped fifth semiconductor region is directly over the ring-shaped third semiconductor region and has the second doping type.