Reflector for a double-pass photodetector

1. An apparatus, comprising:

a substrate;

a photodetector formed on an area of a surface of the substrate;

an electrical contact formed on a portion of the photodetector; and

a reflector formed over a portion of the photodetector distinct from the portion of the photodetector having the electrical contact formed thereon,

wherein:

the substrate, the photodetector, and the reflector are arranged so that an optical signal to be detected is incident on the photodetector from within the substrate, and at least a portion of the optical signal incident on the photodetector and transmitted thereby on a first pass is reflected by the reflector to propagate through the photodetector for a second pass; and

the reflector comprises at least one metal layer electrically insulated from the electrical contact.

2. The apparatus of claim 1 , wherein the substrate includes a reflecting face formed thereon and arranged for directing by internal reflection the optical signal onto the photodetector for the first pass.

3. The apparatus of claim 2 , wherein the reflecting face is arranged for directing by total internal reflection the optical signal onto the photodetector for the first pass.

4. The apparatus of claim 1 , wherein the electrical contact is formed on only a peripheral portion of the photodetector.

5. The apparatus of claim 1 , wherein the reflector comprises a single dielectric layer formed directly on the photodiode, and at least one metal layer formed directly on the dielectric layer.

6. The apparatus of claim 1 , wherein the reflector comprises a dielectric multilayer reflector stack formed directly on the photodetector.

7. The apparatus of claim 6 , wherein the dielectric multilayer reflector stack comprises alternating layers of silicon nitride and silicon.

8. The apparatus of claim 6 , wherein the dielectric multilayer reflector stack comprises alternating layers of two dielectric materials chosen from a group consisting of silicon, silicon oxide, silicon nitride, and silicon oxynitride.

9. The apparatus of claim 6 , wherein the reflector further comprises at least one metal layer formed directly on the dielectric multilayer reflector stack.

10. The apparatus of claim 9 , wherein the metal layer comprises a titanium layer formed directly on the dielectric multilayer reflector stack, a platinum layer formed directly on the titanium layer, and a gold layer formed directly on the platinum layer.

11. The apparatus of claim 9 , wherein the metal layer comprises a titanium layer formed directly on the dielectric multilayer reflector stack, and a gold layer formed directly on the titanium layer.

12. An apparatus, comprising:

a substrate;

a photodetector formed on an area of a surface of the substrate;

an electrical contact formed on a portion of the photodetector; and

a reflector formed over a portion of the photodetector distinct from the portion of the photodetector having the electrical contact formed thereon,

wherein:

the substrate, the photodetector, and the reflector are arranged so that an optical signal to be detected is incident on the photodetector from within the substrate, and at least a portion of the optical signal incident on the photodetector and transmitted thereby on a first pass is reflected by the reflector to propagate through the photodetector for a second pass; and

the reflector comprises a metal layer formed directly on the photodiode.

13. The apparatus of claim 12 , wherein the reflector comprises a titanium layer formed directly on the photodiode, and a gold layer formed directly on the titanium layer.

14. The apparatus of claim 5 , wherein the dielectric layer comprises silicon nitride, silicon oxide, or silicon oxynitride.

15. The apparatus of claim 5 , wherein the metal layer comprises a titanium layer formed directly on the dielectric layer and a gold layer formed directly on the titanium layer.

16. The apparatus of claim 5 , wherein the metal layer comprises an aluminum layer formed directly on the dielectric layer.