Imaging apparatus, imaging system, moving object, and method for manufacturing imaging apparatus

An imaging apparatus comprising:

• a photoelectric conversion unit of a first conductivity type;
• a charge holding unit of the first conductivity type, the charge holding unit being configured to hold electric charges transferred from the photoelectric conversion unit;
• a floating diffusion unit of the first conductivity type, the floating diffusion unit being configured to receive electric charges transferred from the charge holding unit;
• a punch-through prevention layer of a second conductivity type, the punch-through prevention layer being disposed between the charge holding unit and the floating diffusion unit to contact the floating diffusion unit;
• and
• a transfer assistance layer of the second conductivity type, the transfer assistance layer being disposed between the punch-through prevention layer and a surface of a semiconductor substrate,
• wherein an impurity concentration of the transfer assistance layer is lower than an impurity concentration of the punch-through prevention layer.