Photo sensing device and method of fabricating the photo sensing device

1. A photo sensing device, comprising:

a substrate, comprising a silicon layer at a front surface;

a photosensitive member extending into and at least partially surrounded by the silicon layer, wherein the silicon layer comprises:

a first doped region adjacent to a first side of the photosensitive member, wherein the first doped region has a first conductivity type; and

a second doped region adjacent to a second side of the photosensitive member opposite to the first side, wherein the second doped region has a second conductivity type different from the first conductivity type, and the first doped region is apart from the second doped region; and

a composite layer disposed between the photosensitive member and the silicon layer and surrounding the photosensitive member,

wherein the composite layer includes a first material and a second material different from the first material.

2. The photo sensing device of claim 1 , wherein the composite layer includes a first semiconductor layer contacting the silicon layer, and a second semiconductor layer between the first semiconductor layer and the photosensitive member.

3. The photo sensing device of claim 2 , wherein the first semiconductor layer includes the first material, and the second semiconductor layer includes the second material.

4. The photo sensing device of claim 2 , wherein the composite layer includes a third semiconductor layer disposed between the second semiconductor layer and the photosensitive member and including the first material.

5. The photo sensing device of claim 4 , wherein the composite layer includes a fourth semiconductor layer disposed between the third semiconductor layer and the photosensitive member and including the second material.

6. The photo sensing device of claim 1 , wherein the first material is silicon and the second material is germanium.

7. The photo sensing device of claim 1 , wherein a portion of the photosensitive member is protruded from the silicon layer.

8. The photo sensing device of claim 1 , wherein a portion of the composite layer proximal to the first doped region is doped with a dopant having the first conductivity type.

9. The photo sensing device of claim 1 , wherein a portion of the photosensitive member proximal to the first doped region is doped with a dopant having the first conductivity type.

10. A photo sensing device, comprising:

a substrate, comprising a silicon layer at a front surface, wherein the silicon layer comprises:

a first portion; and

a second portion surrounding the first portion, wherein a thickness of the second portion of the silicon layer is greater than a thickness of the first portion of the silicon layer;

a photosensitive member over the first portion of the silicon layer, wherein the silicon layer comprises:

a first doped region adjacent to a first side of the photosensitive member, wherein the first doped region has a first conductivity type; and

a second doped region adjacent to a second side of the photosensitive member opposite to the first side, wherein the second doped region has a second conductivity type different from the first conductivity type, and the first doped region is apart from the second doped region; and

a semiconductor stack between the photosensitive member and the first portion of the silicon layer, wherein the semiconductor stack comprises:

a first semiconductor layer between the first portion of the silicon layer and the photosensitive member; and

a second semiconductor layer between the first semiconductor layer and the photosensitive member.

11. The photo sensing device of claim 10 , further comprising a third semiconductor layer between the second semiconductor layer and the photosensitive member, wherein the third semiconductor layer has a material identical with the first semiconductor layer.

12. The photo sensing device of claim 10 , wherein a first portion of the semiconductor stack is doped with a p-type dopant, and a second portion of the semiconductor stack is doped with an n-type dopant.

13. The photo sensing device of claim 10 , wherein the first semiconductor layer comprises intrinsic silicon, and the second semiconductor layer comprises germanium.

14. A method for forming a photo sensing device, comprising:

forming a recess in a substrate;

forming a first doped region having a first conductivity type in the substrate proximal to a first side of the recess;

forming a second doped region having a second conductivity type in the substrate proximal to a second side of the recess opposite to the first side, wherein the first doped region is apart from the second doped region;

forming a first semiconductor layer conformal to the recess;

forming a second semiconductor layer over the first semiconductor layer; and

forming a photosensitive member within the recess and surrounded by the first semiconductor layer and the second semiconductor layer.

15. The method of claim 14 , further comprising, prior to the formation of the first semiconductor layer and the second semiconductor layer:

forming an oxide layer conformal the recess by oxidizing the substrate; and

removing the oxide layer.

16. The method of claim 15 , wherein forming the first semiconductor layer comprises:

performing a selective epitaxial growth (SEG) operation after removing the oxide layer.

17. The method of claim 15 , wherein the first doped region and the second doped region are formed after oxidizing the substrate.

18. The method of claim 14 , further comprising:

forming a first mask layer over the photosensitive member;

implanting a first dopant having the first conductivity type into the photosensitive member proximal to the first doped region; and

forming a second mask layer over the photosensitive member; and

implanting a second dopant having the second conductivity type into the photosensitive member proximal to the second doped region.

19. The photo sensing device of claim 11 , wherein a thickness of the first semiconductor layer is greater than a thickness of the third semiconductor layer.

20. The photo sensing device of claim 10 , wherein the first doped region comprises a first region and a second region, wherein a dopant concentration in the first region is greater than a dopant concentration in the second region, and a portion of the second region is between the first region and the photosensitive member.