Germanium-based photodetector with reduced dark current and methods of making the same

A method of fabricating a semiconductor device, comprising:

• forming a hard mask layer over a semiconductor material layer;
• forming an opening through the hard mask layer;
• etching the semiconductor material layer through the opening in the hard mask layer to form a trench;
• forming a first-conductivity-type semiconductor material region in the semiconductor material layer along a sidewall and a bottom surface of the trench;
• forming a germanium-containing well within the trench;
• and
• performing an etching process around a periphery of the germanium-containing well to provide a gap between the germanium-containing well and the first-conductivity-type semiconductor material region of the semiconductor material layer.

A method of fabricating a semiconductor device, comprising:

• forming a germanium-based well that includes germanium at an atomic percentage greater than 50% surrounded by a semiconductor material layer that includes germanium at an atomic percentage between 0% and 50%;
• forming a gap between a lateral side surface of the germanium-based well and a sidewall of the surrounding semiconductor material layer;
• and
• forming a passivation layer comprising silicon over a top surface of the germanium-based well and a top portion of the gap between the lateral side surface of the germanium-based well and the sidewall of the surrounding semiconductor material layer, wherein the gap comprises an air gap having an upper surface formed by the passivation layer.