Germanium photodetector embedded in a multi-mode interferometer

A device comprising:

• a silicon region comprising:
• a silicon slab;
• an upper semiconductor region over and joining the silicon slab, wherein the upper semiconductor region is narrower than the silicon slab, and wherein the upper semiconductor region comprises:
• a front portion;
• a back portion;
• and
• a middle portion between, and connecting to, the front portion and the back portion, wherein the middle portion is wider than both of the front portion and the back portion;
• and
• an input port connecting to the front portion.

A device comprising:

• a dielectric layer;
• a semiconductor region over the dielectric layer, the semiconductor region comprising:
• a lower portion;
• and
• an upper portion narrower than the lower portion, wherein the upper portion is over and joined to the lower portion, and wherein the upper portion comprises:
• a first portion having a first width;
• a second portion having a second width greater than the first width, wherein parts of the second portion form a diode;
• and
• a third portion having a third width smaller than the second width;
• and
• an input port connecting to the first portion.