Pixel structure, image sensor, image capturing apparatus, and electronic device

A light detecting sensor, comprising:

• a pixel having a pixel structure of a single photon avalanche photodiode (SPAD), the pixel structure including:
• a first side, wherein the first side is a light incident side;
• a second side, wherein the second side is opposite the first side;
• a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer in that order from the second side of the SPAD towards the first side of the SPAD, wherein the first semiconductor layer is of a second conduction type, wherein the second and third semiconductor layers are of a first conduction type that is opposite to the second conduction type, wherein the first and second semiconductor layers form a junction part, wherein the third semiconductor layer and the first semiconductor layer have a same width in a depth direction, and wherein the third semiconductor layer guides electrons to a charge discharge path on outer sides of the third semiconductor layer so that the electrons propagate directly to the first semiconductor layer without passing through a boundary between the first semiconductor layer and the second semiconductor layer;
• and
• a light absorption layer on the first side of the SPAD.