Apparatus and methods for sensing long wavelength light

1. A semiconductor device, comprising:

a carrier;

a device layer on the carrier;

a semiconductor layer on the device layer, wherein

the semiconductor layer comprises a plurality of isolation regions and a plurality of pixel regions,

each of the plurality of isolation regions comprises a trench isolation and an implanted well surrounding the trench isolation,

the trench isolation comprises a dielectric material,

the implanted well comprises a first semiconductor material, and

the plurality of pixel regions comprises a second semiconductor material that is different from the first semiconductor material; and

an insulation layer on the semiconductor layer.

2. The semiconductor device of claim 1 , wherein the second semiconductor material has a band gap smaller than that of the first semiconductor material.

3. The semiconductor device of claim 1 , wherein:

the plurality of pixel regions are evenly distributed in the semiconductor layer based on a predetermined design; and

each of the plurality of isolation regions is located between two adjacent pixel regions.

4. The semiconductor device of claim 1 , wherein the semiconductor layer comprises a light sensing sublayer including a plurality of light sensing regions, wherein each of the plurality of pixel regions comprises a corresponding one of the plurality of light sensing regions.

5. The semiconductor device of claim 4 , wherein:

each of the plurality of light sensing regions comprises the second semiconductor material and a doping material; and

doping concentrations of the plurality of light sensing regions are different from each other based on a predetermined design.

6. The semiconductor device of claim 4 , wherein:

the semiconductor layer has a first thickness between 2 micrometers and 10 micrometers; and

each of the plurality of light sensing regions in the light sensing sublayer has a second thickness that is equal to or smaller than the first thickness.

7. The semiconductor device of claim 1 , wherein:

the trench isolation is one of: a shallow trench isolation, or a deep trench isolation.

8. The semiconductor device of claim 1 , wherein:

the semiconductor layer has a first surface and a second surface opposite to the first surface that is adjacent to the device layer; and

the second surface has a non-flat and periodic surface structure.

9. An image sensor, comprising:

a device layer including a plurality of devices;

a semiconductor layer on the device layer, wherein the semiconductor layer comprises a silicon region and a plurality of light sensing regions surrounded by the silicon region, wherein

each of the plurality of light sensing regions comprises a same semiconductor material and a same doping material,

doping concentrations of the plurality of light sensing regions are different from each other based on a predetermined design,

the same semiconductor material has a band gap smaller than that of silicon; and

an insulation layer on the semiconductor layer.

10. The image sensor of claim 9 , wherein the same semiconductor material is germanium.

11. The image sensor of claim 9 , wherein the plurality of devices are located below the silicon region without contacting the same semiconductor material in the plurality of light sensing regions.

12. The image sensor of claim 9 , wherein:

the insulation layer comprises silicon oxide to serve as a passivation layer for the semiconductor layer.

13. The image sensor of claim 9 , wherein:

the silicon region is thicker than the plurality of light sensing regions.

14. A method for forming an image sensor, comprising:

forming an insulation layer on a semiconductor substrate;

forming a patterned structure on a first surface of the insulation layer;

epitaxially growing a first semiconductor material on the insulation layer to form a semiconductor layer on and in contact with the first surface of the insulation layer;

etching the semiconductor layer to determine a plurality of etched regions in the semiconductor layer;

epitaxially growing a second semiconductor material in the plurality of etched regions to form a plurality of light sensing regions in the semiconductor layer, wherein the second semiconductor material is different from the first semiconductor material;

forming a dielectric layer over the semiconductor layer to generate a first wafer; and

bonding the first wafer onto a second wafer via the dielectric layer.

15. The method of claim 14 ,

wherein the patterned structure of the first surface increases a quantum efficiency of the image sensor compared to a flat surface structure.

16. The method of claim 14 , further comprising:

doping each of the plurality of light sensing regions such that a doping concentration varies from one light sensing region to another based on a predetermined design.

17. The method of claim 14 , further comprising:

determining, in the semiconductor layer, a plurality of isolation regions each of which is between two adjacent light sensing regions; and

doping each of the plurality of isolation regions to generate an implanted well in the isolation region.

18. The method of claim 17 , further comprising forming a device layer including a plurality of devices on the semiconductor layer, wherein:

the dielectric layer is formed on the device layer; and

each of the plurality of devices is located on one of the plurality of isolation regions.

19. The method of claim 18 , further comprising removing the semiconductor substrate on the insulation layer after the bonding, wherein at least part of the insulation layer is kept to serve as a passivation layer for the semiconductor layer.

20. The method of claim 19 , further comprising:

forming a deep trench in each of the plurality of isolation regions after the bonding, wherein

the at least part of the insulation layer has a top surface and a bottom surface that is opposite to the top surface and is in contact with the semiconductor layer after the bonding, and

the deep trench extends from the top surface of the insulation layer into a corresponding one of the plurality of isolation regions; and

forming an isolation structure in the deep trench in each of the plurality of isolation regions.