The invention relates to a photodetector, an image sensor, and a method of operating the image sensor. A photodetector includes a first doped region disposed in a semiconductor material and a second doped region disposed in the semiconductor material. The second doped region is electrically coupled to the first doped region, and the second doped region is of an opposite majority charge carrier type as the first doped region. The photodetector also includes a quantum dot layer disposed in a trench in the semiconductor material, and the quantum dot layer is electrically coupled to the second doped region. A transfer gate is disposed to permit charge transfer from the second doped region to a floating diffusion.