A photodiode with a heavily doped p+ layer at the surface that keeps the collection region away from the interface. It suppresses dark current from interface states and allows complete charge transfer; it is standard in CMOS image sensors.
The transfer gate moves charge from the pinned photodiode to the floating diffusion (FD), whose voltage the amplifier outputs; reset initializes the FD and select chooses the row.
In the typical four-transistor pixel of a CMOS image sensor…CMOS image sensor Photodiode Correlated double sampling (CDS) Backside illumination (BSI) Bayer pattern CCD image sensor Dark current Fixed-pattern noise Full-well capacity Global shutter