Germanium/silicon avalanche photodetector with separate absorption and multiplication regions

A method, comprising:

• illuminating with light a first type of semiconductor material of an absorption region;
• absorbing a first range of wavelengths of the light in the first type of semiconductor material;
• passing unabsorbed light from the first type of semiconductor material into a second type of semiconductor material of the absorption region;
• absorbing a second range of wavelengths of the unabsorbed light passed from the first type of semiconductor material into the second type of semiconductor material;
• and
• selectively multiplying electrons generated in the absorption region that drift into a multiplication region from the absorption region.

A system, comprising:

• an array of photodetectors, each of the photodetectors including:
• a first region including a first type of semiconductor material proximate to a second type of semiconductor material, the first type of semiconductor material to absorb light in a first range of wavelengths and the second type of semiconductor material to absorb light in a second range of wavelengths;
• and
• a second region proximate to and separate from the first region, the second region including an intrinsic semiconductor material to multiply electrons from the first region when there is an electric field;
• and
• an optical focusing element to focus an image onto the array of photodetectors.