Semiconductor device with nanostructures and methods of forming the same

1. A semiconductor device, comprising:

a photo sensing region having a first dopant; and

a semiconductor substrate laterally surrounding the photo sensing region and having a second dopant that is of a different conductivity type than the first dopant; and

a plurality of nanostructures embedded in the photo sensing region and having top surfaces level with a top surface of the photo sensing region.

2. The semiconductor device of claim 1 , wherein the top surfaces of the plurality of nanostructures are also level with a top surface of the semiconductor substrate.

3. The semiconductor device of claim 1 , wherein the plurality of nanostructures each have a bottom surface higher than a bottommost position of the photo sensing region.

4. The semiconductor device of claim 1 , wherein the plurality of nanostructures are spaced apart from each other by the photo sensing region.

5. The semiconductor device of claim 1 , wherein the plurality of nanostructures each have a triangular cross section.

6. The semiconductor device of claim 1 , further comprising a dielectric layer over the plurality of nanostructures and laterally extending across an interface between the semiconductor substrate and the photo sensing region.

7. A semiconductor device, comprising:

a semiconductor substrate;

a photo sensing region in the semiconductor substrate, the photo sensing region having a plurality of recesses; and

a plurality of nanostructures filling up the plurality of recesses of the photo sensing region, respectively, wherein the plurality of nanostructures are made of a semiconductor material.

8. The semiconductor device of claim 7 , wherein a top surface of each of the plurality of nanostructures is level with a top surface of the photo sensing region.

9. The semiconductor device of claim 7 , wherein a top surface of each of the plurality of nanostructures is level with a top surface of the semiconductor substrate.

10. The semiconductor device of claim 7 , wherein the semiconductor material of the plurality of nanostructures is different from the semiconductor substrate.

11. The semiconductor device of claim 7 , wherein the plurality of nanostructures are made of silicon germanium.

12. The semiconductor device of claim 7 , wherein the plurality of nanostructures each have a lateral dimension in a range from 400 nm to 700 nm.

13. The semiconductor device of claim 7 , wherein each of the plurality of nanostructures has a circular top-view profile.

14. The semiconductor device of claim 7 , wherein each of the plurality of nanostructures has a rectangular cross-sectional profile.

15. The semiconductor device of claim 7 , further comprising a dielectric layer over the plurality of nanostructures, the dielectric layer extending laterally across an interface between the semiconductor substrate and the photo sensing region.

16. A semiconductor device, comprising:

a semiconductor substrate of a first conductivity type;

a photo sensing region in the semiconductor substrate, the photo sensing region being of a second conductivity type different than the first conductivity type; and

a plurality of nanopillars inlaid in the photo sensing region, wherein the plurality of nanopillars are made of a different material than the photo sensing region.

17. The semiconductor device of claim 16 , wherein a top surface of each of the plurality of nanopillars is level with a top surface of the photo sensing region.

18. The semiconductor device of claim 16 , wherein a height of each of the plurality of nanopillars is smaller than a height of the photo sensing region.

19. The semiconductor device of claim 16 , wherein the plurality of nanopillars are made of a semiconductor material.

20. The semiconductor device of claim 16 , wherein the plurality of nanopillars are made of silicon germanium.