Photoelectric conversion device

A photoelectric conversion device comprising:

• a photoelectric conversion unit including
• a first semiconductor region of a first conductivity type having carriers of same polarity as a signal charge as majority carriers,
• a second semiconductor region of a second conductivity type forming a p-n junction with the first semiconductor region, and
• a third semiconductor region of the first conductivity type forming a p-n junction with the second semiconductor region;
• and
• a control circuit configured to switch a reverse bias voltage, applied between the first semiconductor region and the second semiconductor region, between a first voltage and a second voltage larger than the first voltage,
• wherein the photoelectric conversion device is configured to perform
• a signal accumulation operation period of accumulating a signal charge generated by an incidence of a photon on the photoelectric conversion unit in the third semiconductor region by setting the reverse bias voltage to the first voltage less than a breakdown voltage of the p-n junction between the first semiconductor region and the second semiconductor region, and
• a signal readout operation period of enabling a transfer of the signal charge from the third semiconductor region to the first semiconductor region and an avalanche multiplication at the p-n junction between the first semiconductor region and the second semiconductor region by setting the reverse bias voltage to the second voltage greater than the breakdown voltage, and
• wherein the control circuit is configured to switch the reverse bias voltage between the first voltage and the second voltage by changing a waveform in a rectangular shape.