Avalanche photodiodes

1 . An avalanche photodiode comprising:

a p-doped substrate;

a first n-doped region positioned above at least a portion of the p-doped substrate;

an n-doped epitaxial region positioned above at least a portion of the first n-doped region;

a plurality of n-doped wells positioned within the n-doped epitaxial region; and

a first p-doped region positioned above the n-doped epitaxial region and the plurality of n-doped wells;

wherein at least one of:

the first p-doped region has a higher doping concentration than the p-doped substrate;

the first p-doped region comprises SiGe; or

the p-doped substrate, the first n-doped region, the n-doped epitaxial region, and the plurality of n-doped wells each comprise silicon and the first p-doped region comprises SiGe.

2 . The avalanche photodiode of claim 1 , wherein at least one of:

the p-doped substrate is a p-doped silicon substrate;

the first p-doped region forms an anode of the avalanche photodiode;

the first n-doped region forms at least a portion of a cathode of the photodiode;

the first n-doped region has a higher doping concentration than a doping concentration of the n-doped epitaxial region; or

the first n-doped region has a higher doping concentration than a doping concentration of the plurality of n-doped wells.

3 . The avalanche photodiode of claim 1 , wherein at least one of:

the plurality of n-doped wells extend along a length of the n-doped epitaxial region; or

the avalanche photodiode achieves a maximum responsivity-bandwidth product of 25-35 A/W×MHz at wavelengths between 1000-1100 nm.

4 . The avalanche photodiode of claim 1 , wherein the first n-doped region, the n-doped epitaxial region, the plurality of n-doped wells, and the first p-doped region have a combined thickness of less than 2 microns.

5 . An avalanche photodiode comprising:

a p-doped substrate;

a first n-doped region positioned above at least a portion of the p-doped substrate;

an n-doped epitaxial region positioned above at least a portion of the first n-doped region;

a plurality of n-doped wells positioned within the n-doped epitaxial region;

a first p-doped region positioned above the n-doped epitaxial region and the plurality of n-doped wells; and

a plurality of shallow trench isolations positioned beneath the first p-doped region and extending into at least a portion of n-doped epitaxial region.

6 . The avalanche photodiode of claim 5 , wherein at least one of:

the p-doped substrate is a p-doped silicon substrate;

the first p-doped region forms an anode of the avalanche photodiode;

the first n-doped region forms at least a portion of a cathode of the photodiode;

the first n-doped region has a higher doping concentration than a doping concentration of the n-doped epitaxial region; or

the first n-doped region has a higher doping concentration than a doping concentration of the plurality of n-doped wells.

7 . The avalanche photodiode of claim 5 , wherein at least one of:

the first p-doped region has a higher doping concentration than the p-doped substrate;

the first p-doped region comprises SiGe; or

the first p-doped region forms an anode of the avalanche photodiode.

8 . The avalanche photodiode of claim 5 , wherein at least one of:

the plurality of n-doped wells extend along a length of the n-doped epitaxial region; or

the avalanche photodiode achieves a maximum responsivity-bandwidth product of 25-35 A/W×MHz at wavelengths between 1000-1100 nm.

9 . The avalanche photodiode of claim 5 , wherein the p-doped substrate, the first n-doped region, the n-doped epitaxial region, and the plurality of n-doped wells each comprise silicon and the first p-doped region comprises SiGe.

10 . The avalanche photodiode of claim 5 further comprising:

a second p-doped region positioned above at least a portion of the p-doped substrate;

wherein the second p-doped region extends around a perimeter of at least a portion of the n-doped region and the n-doped epitaxial region.

11 . The avalanche photodiode of claim 10 , wherein at least one of:

the second p-doped region has a higher doping concentration than a doping concentration of the p-doped substrate; or

the second p-doped region has a higher doping concentration than a doping concentration of the first p-doped region.

12 . The avalanche photodiode of claim 5 , wherein the n-doped region, the n-doped epitaxial region, the plurality of n-doped wells, and the first p-doped region have a combined thickness of less than 2 microns.

13 . An avalanche photodiode comprising:

a p-doped substrate;

a first n-doped region positioned above at least a portion of the p-doped substrate;

an n-doped epitaxial region positioned above at least a portion of the first n-doped region;

a plurality of n-doped wells positioned within the n-doped epitaxial region;

a first p-doped region positioned above the n-doped epitaxial region and the plurality of n-doped wells; and

a second p-doped region positioned above at least a portion of the p-doped substrate;

wherein the second p-doped region extends around a perimeter of at least a portion of the first n-doped region and the n-doped epitaxial region.

14 . The avalanche photodiode of claim 13 , wherein at least one of:

the second p-doped region has a higher doping concentration than a doping concentration of the p-doped substrate; or

the second p-doped region has a higher doping concentration than a doping concentration of the first p-doped region.

15 . The avalanche photodiode of claim 13 further comprising:

a second n-doped region positioned above at least a portion of the first n-doped region;

wherein:

the second n-doped region extends around a perimeter of at least a portion of the n-doped epitaxial region; and

the second p-doped region extends around a perimeter of at least a portion of the second n-doped region.

16 . The avalanche photodiode of claim 13 further comprising:

a third p-doped region positioned above at least a portion of the second p-doped region;

wherein the third p-doped region has a higher doping concentration than a doping concentration of the second p-doped region.

17 . An avalanche photodiode comprising:

a p-doped silicon substrate;

an n-doped silicon region positioned above at least a portion of the p-doped silicon substrate and forming at least a portion of a cathode of the avalanche photodiode;

an n-doped epitaxial silicon region positioned above at least a portion of the first n-doped silicon region;

a plurality of n-doped silicon wells positioned within the n-doped epitaxial silicon region;

a p-doped silicon region positioned above the n-doped epitaxial silicon region and the plurality of n-doped silicon wells;

a plurality of shallow trench isolations positioned beneath the p-doped silicon region and extending into at least a portion of the n-doped epitaxial silicon region; and

a p-doped SiGe region positioned above the n-doped epitaxial silicon region and the plurality of n-doped silicon wells and forming an anode of the avalanche photodiode;

wherein:

the n-doped silicon region has a higher doping concentration than a doping concentration of both the n-doped epitaxial silicon region and the plurality of n-doped silicon wells; and

the p-doped SiGe region has a higher doping concentration than the p-doped silicon substrate.

18 . The avalanche photodiode of claim 17 , wherein the avalanche photodiode achieves a maximum responsivity-bandwidth product of 25-35 A/W×MHz at wavelengths between 1000-1100 nm.

19 . The avalanche photodiode of claim 17 , wherein the n-doped silicon region, the n-doped epitaxial silicon region, the plurality of n-doped silicon wells, and the p-doped silicon region have a combined thickness of less than 2 microns.