Photo-detecting apparatus with low dark current

1. A photo-detecting apparatus, comprising:

a 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 having a first edge and a second edge that is opposite to the first edge,

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 an optical signal and to generate photo-carriers in response to 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 and closer to the first edge than to the second edge 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 and closer to the second edge than to the first edge for collecting photo-carriers of a second type.

2. The photo-detecting apparatus according to claim 1 , further comprising:

a first electrode formed over the first carrier collection region; and

a second electrode formed over the second carrier collection region,

wherein each of the first electrode and the second electrode is separated from the absorption region, and

wherein the first electrode is electrically coupled to the first carrier collection region and configured to collect a first portion of the photo-carriers, and the second electrode is electrically coupled to the second carrier collection region and configured to collect a second portion of the photo-carriers.

3. The photo-detecting apparatus according to claim 2 , wherein the carrier conducting region has a depth less than 5 μm, and

wherein the carrier conducting region is formed between the first carrier collection region and the absorption region to transport the first portion of the photo-carriers from the absorption region to the first carrier collection region, and

wherein the carrier conducting region is formed between the second carrier collection region and the absorption region to transport the second portion of the photo-carriers from the absorption region to the second carrier collection region.

4. The photo-detecting apparatus according to claim 1 , wherein at least a part of the top surface, the bottom surface, the first side, or the second side is in contact with the carrier conducting region.

5. The photo-detecting apparatus according to claim 1 , wherein the absorption region is doped with a graded doping profile.

6. The photo-detecting apparatus according to claim 1 , wherein at least 50% of the absorption region is p-doped with a doping concentration equal to or greater than 1×10 16 cm −3 .

7. The photo-detecting apparatus according to claim 1 , wherein the first material includes germanium, and the second material includes silicon.

8. The photo-detecting apparatus according to claim 1 , wherein a ratio of a doping concentration of the absorption region to a doping concentration of the carrier conducting region at the heterointerface is equal to or more than 10.

9. The photo-detecting apparatus according to claim 1 , wherein the third carrier collection region is p-doped with a fourth peak doping concentration higher than the first peak doping concentration, and

wherein the photo-detecting apparatus further comprises a second electrode formed over a top surface of the substrate, and wherein the second electrode is electrically coupled to the third carrier collection region.

10. The photo-detecting apparatus according to claim 9 , wherein a part of the third carrier collection region is covered by the absorption region, wherein the absorption region has a width, and wherein a width of the third carrier collection region covered by the absorption region is equal to or more than half of the width of the absorption region.

11. The photo-detecting apparatus according to claim 1 , wherein at least a part of the carrier conducting region is between one of the first carrier collection region and the second carrier collection region and the absorption region.

12. The photo-detecting apparatus according to claim 2 , wherein a nearest distance between one of the first electrode and the second electrode and one of the first side and the second side of the absorption region is between 0.1 μm and 20 μm.

13. The photo-detecting apparatus according to claim 1 , wherein the optical signal has a peak wavelength in an invisible wavelength range equal to or greater than 800 nm.

14. 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.