Photodetector

1. A photodetector comprising:

a substrate;

a first doped region in an upper portion of the substrate;

a second doped region having a ring structure, wherein the second doped region is provided in the substrate, surrounds the first doped region, and is horizontally spaced apart from the first doped region;

an optical absorption layer on the first doped region, the optical absorption layer absorbing photons to generate an electrical signal;

a contact layer on the optical absorption layer;

a first electrode on the contact layer; and

a second electrode on the second doped region,

wherein the first doped region has a first conductive type and directly contacts the optical absorption layer, and the second doped region has a second conductive type,

wherein top surfaces of the first and second doped regions and the substrate are coplanar with each other, and

wherein a magnitude of the electrical signal is amplified under the first doped region.

2. The photodetector of claim 1 , further comprising a third doped region having a ring structure, wherein the third doped region is provided in the substrate, surrounds the first doped region, and is disposed between the first doped region and the second doped region, and

wherein the substrate is an intrinsic silicon substrate, and the third doped region has the first conductive type.

3. The photodetector of claim 2 , wherein the first conductive type is a p type and the second conductive type is an n type.

4. The photodetector of claim 1 , further comprising:

a third doped region having a ring structure and disposed in the substrate; and

a fourth doped region disposed under the first doped region and in the substrate; and

wherein the third doped region surrounds the first doped region and the fourth doped region, and

wherein the third doped region has the first conductive type, the substrate is a second conductive type silicon substrate, the fourth doped region has the second conductive type, and the doping concentration of the fourth doped region is higher than that of the substrate.

5. The photodetector of claim 4 , wherein the first conductive type is a p type and the second conductive type is an n type.

6. The photodetector of claim 1 , wherein the first doped region has a plurality of rings when viewed from a top.

7. The photodetector of claim 6 , wherein depths of lower surfaces of the plurality of rings are different from one another.

8. The photodetector of claim 6 , wherein the plurality of rings has different doping concentrations.

9. The photodetector of claim 1 , wherein the optical absorption layer comprises any one selected from among germanium (Ge), gallium arsenic (GaAs), indium phosphide (InP), and indium gallium arsenic (InGaAs).

10. The photodetector of claim 1 , further comprising an etched guard ring having a ring structure, wherein the etched guard ring protrudes from the substrate and surrounds the first doped region, and

wherein the substrate and the etched guard ring include intrinsic silicon.

11. A photodetector comprising:

a substrate;

an optical waveguide protruding from the substrate and extending in a first direction;

a first doped region in an upper portion of the optical waveguide;

second doped regions being spaced apart from the optical waveguide in a second direction intersecting the first direction;

an optical absorption layer on the first doped region, the optical absorption layer absorbing photons to generate an electrical signal; and

a contact layer on the optical absorption layer,

wherein the substrate comprises a buried oxide layer,

wherein a magnitude of the electrical signal is amplified under the first doped region, and

wherein the first doped region has a first conductive type and directly contacts the optical absorption layer, and the second doped regions have a second conductive type.

12. The photodetector of claim 11 , wherein the substrate and the optical waveguide include intrinsic silicon.

13. The photodetector of claim 11 , further comprising a third doped region provided in the substrate and under the first doped region,

wherein the third doped region has the second conductive type, and the substrate and the optical waveguide include second conductive type silicon.

14. The photodetector of claim 13 , wherein the first conductive type is a p type and the second conductive type is an n type.

15. The photodetector of claim 4 , wherein the third doped region directly contacts the first and fourth doped regions.

16. The photodetector of claim 4 , wherein the doping concentration of the fourth doped region is in a range from 10 14 cm −3 to 10 21 cm −3 .

17. The photodetector of claim 16 , wherein the doping concentration of the fourth doped region is in a range from 10 16 cm −3 to 10 21 cm −3 .

18. The photodetector of claim 11 , wherein a top surface of the first doped region is substantially coplanar with a top surface of the optical waveguide.

19. The photodetector of claim 1 , wherein the optical absorption layer and the contact layer have a vertically uniform sidewall.

20. The photodetector of claim 11 , wherein the optical absorption layer and the contact layer have a vertically uniform sidewall.