Photonic device formed using self-aligned processes

A structure, comprising:

• a substrate;
• a P-type contact disposed over the substrate in a vertical direction, wherein the P-type contact contains silicon;
• an N-type contact disposed over the substrate in the vertical direction, wherein the N-type contact contains silicon;
• an optical absorption layer disposed over the substrate in the vertical direction and between the P-type contact and the N-type contact in a horizontal direction, wherein the optical absorption layer contains germanium;
• and
• a charging layer disposed over the substrate in the vertical direction and between the optical absorption layer and the N-type contact in the horizontal direction, wherein the charging layer contains silicon that is doped with a P-type dopant, and wherein an interface between the optical absorption layer and the charging layer extends substantially in the vertical direction.

A method, comprising:

• forming a semiconductor layer over a substrate;
• etching an opening in the semiconductor layer;
• forming, using a selective growth process, an optical absorption layer on a portion of the semiconductor layer exposed by the opening;
• forming a charging layer that is abutting the optical absorption layer, the charging layer forming a substantially straight interface with the optical absorption layer and a portion of the semiconductor layer;
• and
• forming a passivation layer over the optical absorption layer and the charging layer.