LIGHT DETECTION DEVICE AND LIGHT DETECTION SYSTEM

There are provided a light detection device and a photoelectric conversion system including the light detection device including an avalanche diode including a first semiconductor region of a first conductivity type disposed at a first depth, a second semiconductor region of a second conductivity type disposed at a second depth deeper than the first depth with respect to the first surface, a third semiconductor region that is disposed at a third depth deeper than the second depth with respect to the first surface and is in contact with the second semiconductor region, and first and second separation regions each extending from the first depth to the third depth. The second semiconductor region and the third semiconductor region each extend from the first separation region to the second separation region. The first semiconductor region, the second semiconductor region, and the third semiconductor region have portions overlapping one another in planar view.