Photo-detecting apparatus with low dark current

A time-of-flight system, comprising:

• a transmitter configured to transmit an optical signal having a peak wavelength in an invisible wavelength range equal to or greater than 800 nm;
• and
• a receiver comprising a photo-detecting device, the photo-detecting device comprising:
• a substrate comprising:
• a carrier conducting region,
• a first switch comprising a first control region and a first carrier collection region,
• a second switch comprising a second control region and a second carrier collection region, and
• a third carrier collection region;
• an absorption region at least partially embedded in the substrate, the absorption region comprising:
• a top surface,
• a bottom surface that is in physical contact with at least a portion of the carrier conducting region to form a heterointerface,
• a first side between the top surface and the bottom surface, and
• a second side that is opposite to the first side,
• wherein the absorption region is configured to receive a portion of the optical signal and to generate photo-carriers in response to the portion of the optical signal, and wherein the absorption region is formed using a first material, and the substrate is formed using a second material having a bandgap greater than a bandgap of the first material,
• wherein the absorption region is p-doped with a first peak doping concentration,
• wherein the carrier conducting region is n-doped with a second peak doping concentration,
• wherein the first carrier collection region and the second carrier collection region are n-doped with a third peak doping concentration higher than the second peak doping concentration,
• wherein the third carrier collection region is p-doped,
• wherein a ratio between the first peak doping concentration of the absorption region and the second peak doping concentration of the carrier conducting region is equal to or greater than 10,
• wherein the first switch and the second switch are disposed at the first side of the absorption region for collecting photo-carriers of a first type, and
• wherein the third carrier collection region is disposed at the second side of the absorption region for collecting photo-carriers of a second type.