Photodetector structures including cross-sectional waveguide boundaries

A photodetector structure comprising:

• a first silicon layer having a trench filled with a cladding material;
• a second silicon layer formed on the cladding material;
• and
• a germanium layer formed in a trench, which is formed by etching the cladding material, to contact a side of the second silicon layer, at which the second silicon layer is etched.

A photodetector structure comprising:

• a silicon substrate;
• a silicon layer on the silicon substrate comprising a first portion of an optical transmission medium including a silicon cross-sectional transmission face;
• and
• a germanium layer on the silicon substrate comprising a second portion of the optical transmission medium, adjacent to the first portion, including a germanium cross-sectional transmission face butt-coupled to the silicon cross-sectional transmission face.