Semiconductor device for light detection

1. A semiconductor device for light detection comprising:

a photodiode comprising an optical active region; and

a resistor connected to said photodiode and overlapping at least a part of said optical active region, wherein the resistor comprises an anti-reflective coating for reducing reflection loss,

wherein the resistor comprises a patterned polysilicon layer comprising a plurality of holes, wherein said holes are filed with silicon oxide (SiO2).

2. A semiconductor device according to claim 1 , wherein said resistor comprises an effective medium having a refractive index between 1.4 and 3.5 for light in the visible spectrum.

3. A semiconductor device according to claim 1 , wherein said resistor has a resistance in the range of 30 kΩ to 150 kΩ.

4. A semiconductor device according to claim 1 , wherein said holes have a width in the range of 200 nm to 700 nm, and wherein a spacing between neighbouring holes is in the range of 90 nm and 300 nm.

5. A semiconductor device according to claim 1 , wherein said polysilicon layer has a thickness in the range of 100 nm and 350 nm.

6. A semiconductor device according to claim 1 , wherein said holes are one of square, round and hexagonal.

7. A semiconductor device according to claim 1 further comprising a contact stop layer comprising silicon nitride (Si3N4) or silicon oxynitride (SIGN) located on said resistor, and a silicon oxide layer located on said contact stop layer.

8. A silicon photomultiplier (SiPM) comprising an array of a plurality of the semiconductor device of claim 1 .

9. A semiconductor device according to claim 1 , wherein the semiconductor device is a Single Photon Avalanche Diode (SPAD).

10. A semiconductor device according to claim 1 , wherein the resistor is configured to quench an avalanche current in the photodiode when in use.

11. A method of forming a semiconductor device for light detection, the method comprising:

providing a silicon layer;

doping said silicon layer so as to form a photodiode comprising an optical active region;

forming a resistor overlapping at least a part of said optical active region, wherein the resistor is formed from an anti-reflective coating for reducing reflection loss; and

connecting said resistor to said photodiode,

wherein forming said resistor comprises:

depositing a polysilicon layer;

patterning said polysilicon layer to form a plurality of holes extending through said polysilicon layer; and

filling said holes with silicon oxide (SiO2) so that the resistor comprises an effective medium having a refractive index between 1.4 and 3.5 for light in the visible spectrum.

12. A method according to claim 11 , wherein said method is performed as part of a standard Complementary Metal Oxide Semiconductor (CMOS) process, and wherein said step of patterning said polysilicon layer comprises using the “POLY” mask of the CMOS process.

13. A method according to claim 11 , further comprising designing said resistor to have a target resistance and a target refractive index.