Pixel cell for image sensor with vertical transfer gate

A pixel cell for an image sensor, comprising:

• a photodiode disposed within a semiconductor substrate, the semiconductor substrate including a first side and a second side opposite the first side, wherein the photodiode includes a shallow doped region and a deep doped region, each having a same conductivity type, and wherein the shallow doped region is disposed between the first side of the semiconductor substrate and the deep doped region;
• a transfer gate coupled to the photodiode, the transfer gate including a vertical portion extending into the semiconductor substrate adjacent to the shallow doped region and from the first side towards the deep doped region of the photodiode,
• wherein, when the pixel cell is viewed from a plan view, the shallow doped region includes a base segment and a protrusion extending from the base segment, wherein the protrusion is separated from the vertical portion by a first lateral separation distance and the base segment is separated from the vertical portion by a second lateral separation distance different from the first lateral separation distance.