Photodetector with reflector with air gap adjacent photodetecting region

1. A photodetector, comprising:

a photodetecting region in a semiconductor substrate; and

a reflector extending at least partially along a sidewall of the photodetecting region in the semiconductor substrate, the reflector including an air gap defined in the semiconductor substrate, wherein the air gap includes a pinch off closure including a semiconductor.

2. The photodetector of claim 1 , wherein the air gap is oriented parallel to a path of incident electromagnetic radiation.

3. The photodetector of claim 1 , wherein the air gap extends vertically along substantially all of the sidewall of the photodetecting region.

4. The photodetector of claim 1 , wherein the air gap extends vertically along a portion of the sidewall of the photodetecting region.

5. The photodetector of claim 1 , wherein the air gap includes a plurality of interconnected voids in the semiconductor substrate.

6. The photodetector of claim 1 , wherein the air gap includes a concave inner surface.

7. The photodetector of claim 1 , wherein the air gap includes a plurality of interconnected internal surfaces creating a polygonal cross-section.

8. The photodetector of claim 1 , wherein the air gap surrounds the photodetecting region.

9. The photodetector of claim 1 , wherein the air gap includes a plurality of spaced air gaps surrounding the photodetecting region.

10. The photodetector of claim 1 , further comprising a liner along at least a portion of an inner surface of the air gap.

11. The photodetector of claim 10 , wherein the liner includes at least one of: a dielectric and an anti-reflective layer.

12. The photodetector of claim 1 , wherein the air gap is defined in a dielectric within a deep trench.

13. The photodetector of claim 1 , wherein the semiconductor substrate includes an n-type semiconductor, and the photodetecting region includes one of: intrinsic germanium, and intrinsic germanium in a p-type semiconductor liner, and

wherein the photodetecting region further includes a p-type semiconductor layer over the one of: intrinsic germanium, and intrinsic germanium in the p-type semiconductor liner.

14. A method, comprising:

forming a photodetecting region in a semiconductor substrate; and

forming a reflector extending at least partially along a sidewall of the photodetecting region in the semiconductor substrate, the reflector including an air gap defined in the semiconductor substrate, and

wherein forming the reflector includes forming an opening in the semiconductor substrate using a crystallographic etch, and sealing the opening to form the air gap with a pinch off closure including semiconductor.

15. The method of claim 14 , wherein forming the photodetecting region occurs prior to forming the reflector.

16. The method of claim 14 , wherein forming the reflector includes forming an opening in the semiconductor substrate, forming a liner on at least a portion of an inner surface of the opening, and sealing the opening to form the air gap.

17. The method of claim 14 , wherein forming the reflector includes forming a plurality of air gaps surrounding the photodetecting region.

18. The method of claim 14 , wherein forming the reflector includes forming an opening in the semiconductor substrate using a crystallographic etch, and sealing the opening to form the air gap.

19. A photodetector, comprising:

a photodetecting region in a semiconductor substrate wherein the semiconductor substrate includes an n-type semiconductor, and wherein the photodetecting region includes one of: intrinsic germanium and intrinsic germanium in a p-type semiconductor liner, and further includes a p-type semiconductor layer over the one of: intrinsic germanium and intrinsic germanium in the p-type semiconductor liner; and

a reflector extending at least partially along a sidewall of the photodetecting region in the semiconductor substrate, the reflector including an air gap defined in the semiconductor substrate.