Avalanche photodiode

An avalanche photodiode comprising:

• a first-conductivity-type semiconductor layer formed within a first-conductivity-type semiconductor substrate;
• a first second-conductivity-type semiconductor layer formed within the semiconductor substrate so as to surround, in plan view for the semiconductor substrate, with a gap width, the first-conductivity-type semiconductor layer,
• a second second-conductivity-type semiconductor layer formed, within the semiconductor substrate, deeper than the first-conductivity-type semiconductor layer and in contact with at least a portion of a bottom portion of the first-conductivity-type semiconductor layer;
• a third second-conductivity-type semiconductor layer formed, within the semiconductor substrate, deeper than the second second-conductivity-type semiconductor layer and in contact with a bottom portion of the second second-conductivity-type semiconductor layer;
• and
• a virtual guard ring formed between the first-conductivity-type semiconductor layer and the first second-conductivity-type semiconductor layer and having a lower concentration than the third second-conductivity-type semiconductor layer,
• wherein the first-conductivity-type semiconductor layer and the second second-conductivity-type semiconductor layer form an avalanche junction,
• the first second-conductivity-type semiconductor layer and the third second-conductivity-type semiconductor layer are connected together such that the semiconductor substrate and the first-conductivity-type semiconductor layer are electrically isolated from each other, and
• the second second-conductivity-type semiconductor layer is smaller than, in plan view for the semiconductor substrate, the bottom portion of the first-conductivity-type semiconductor layer.

An avalanche photodiode comprising:

• a first-conductivity-type semiconductor layer formed within a first-conductivity-type semiconductor substrate;
• a first second-conductivity-type semiconductor layer formed within the semiconductor substrate so as to surround, in plan view for the semiconductor substrate, with a gap width, the first-conductivity-type semiconductor layer,
• a second second-conductivity-type semiconductor layer formed, within the semiconductor substrate, deeper than the first-conductivity-type semiconductor layer and in contact with at least a portion of a bottom portion of the first-conductivity-type semiconductor layer;
• a third second-conductivity-type semiconductor layer formed, within the semiconductor substrate, deeper than the second second-conductivity-type semiconductor layer and in contact with a bottom portion of the second second-conductivity-type semiconductor layer;
• and
• a fourth second-conductivity-type semiconductor layer formed between the first second-conductivity-type semiconductor layer and the third second-conductivity-type semiconductor layer so as to be in contact with at least a portion of a bottom portion of the first second-conductivity-type semiconductor layer, and having a higher concentration than a portion of the first second-conductivity-type semiconductor layer, the portion being in contact with the fourth second-conductivity-type semiconductor layer, and than a portion of the third second-conductivity-type semiconductor layer, the portion being in contact with the fourth second-conductivity-type semiconductor layer;
• and
• a fifth second-conductivity-type semiconductor layer formed in an upper portion of the first second-conductivity-type semiconductor layer and having a higher impurity concentration than the first second-conductivity-type semiconductor layer,
• wherein the first-conductivity-type semiconductor layer and the second second-conductivity-type semiconductor layer form an avalanche junction,
• the first second-conductivity-type semiconductor layer and the third second-conductivity-type semiconductor layer are connected together such that the semiconductor substrate and the first-conductivity-type semiconductor layer are electrically isolated from each other, and
• the fourth second-conductivity-type semiconductor layer electrically connects together the first second-conductivity-type semiconductor layer and the third second-conductivity-type semiconductor layer.