Method of operating an avalanche photodiode for reducing gain normalized dark current

1. A method of operating an avalanche photodiode in an avalanche gain mode for reducing dark current noise, wherein the photodiode has a gain normalized dark current, wherein the photodiode has sources of dark current that are dominant when a reverse bias below an avalanche gain threshold voltage is applied to the photodiode, wherein the gain normalized dark current of the photodiode attributable to the dominant sources of the dark current is not multiplied by gain of the photodiode, the method comprising: applying a selected reverse bias to the photodiode to cause the photodiode to operate in the avalanche gain mode and to have a gain that reduces the gain normalized dark current of the photodiode, wherein the selected reverse bias is beyond a range in which gain and dark current both increase or decrease simultaneously.

2. The method of claim 1 , wherein the photodiode includes a photon absorption region coupled to a carrier multiplication region, wherein the dominant sources of the dark current are substantially comprised of at least one of generation-recombination current and diffusion current generated in the carrier multiplication region.

3. The method of claim 1 , wherein the photodiode has an excess noise factor that is substantially gain independent.

4. The method of claim 2 , wherein the photodiode includes an intrinsic region interposed between and coupled to the absorption region and the carrier multiplication region.

5. The method of claim 4 , wherein the absorption and carrier multiplication regions have a homojunction semiconductor architecture.

6. The method of claim 4 , wherein the absorption and carrier multiplication regions have a heterojunction semiconductor architecture.

7. The method of claim 2 , wherein the absorption region is a p+ region, and the intrinsic region is an n− region.

8. The method of claim 2 , wherein the absorption region is a n+ region, and the intrinsic region is an p− region.

9. The method of claim 1 , wherein the photodiode is a HgCdTe avalanche photodiode.

10. The method of claim 1 , wherein the selected reverse bias corresponds to a minimized gain normalized dark current for the photodiode that achieves an optimized signal-to-noise level for the photodiode.

11. The method of claim 1 , wherein the photodiode has an excess noise factor that is gain dependent.

12. The method of claim 1 , wherein the step of applying a selected reverse bias comprises:

a) applying a plurality of increasing levels of reverse bias to the photodiode, where each reverse bias level causes an increase in gain for the photodiode;

b) observing the gain normalized dark current of the photodiode for at least the last two applied reverse bias levels to determine whether the gain normalized dark current has been reduced; and

c) increasing the level of reverse bias applied to the photodiode to obtain the selected reversed bias in response to determining that the gain normalized dark current has been reduced.

13. The method of claim 12 , further comprising repeating the observing step and the increasing step until the observed gain normalized dark current is no longer being reduced.

14. The method of claim 13 , wherein the selected reverse bias applied to the photodiode is greater than 8 volts.

15. The method of claim 1 , wherein the selected reverse bias applied to the photodiode is equal to or greater than 8 volts such that photodiode has a gain greater than 100 times an input voltage corresponding to a charge absorbed by the photodiode, while the gain normalized dark current is reduced to less than 100 nA/cm 2 or less.

16. The method of claim 1 , wherein the selected reverse bias applied to the photodiode is equal to or greater than 10 volts such that photodiode has a gain greater than 100 times an input voltage corresponding to a charge absorbed by the photodiode, while the gain normalized dark current is reduced to 3.4 nA/cm 2 or less.