Sidewall photodetector

1. A photonic device, comprising:

a substrate semiconductor film with first and second trench sidewalls formed therein;

a first photodetector including a first p-i-n film stack disposed over the first trench sidewall, wherein the first p-i-n film stack comprises a first i-layer semiconductor film having a band gap to absorb at least a portion of light incident to the first trench sidewall having a first wavelength and to pass at least a portion of the incident light having a second wavelength;

a second photodetector including a second p-i-n film stack disposed over the second trench sidewall, wherein the second p-i-n film stack comprises a second i-layer semiconductor film having a band gap different than that of the first i-layer semiconductor film to absorb at least a portion of light having the second wavelength; and

an optical waveguide formed in the substrate semiconductor film and spanning at least a portion of a distance between the first and the second photodetectors to optically couple to the second sidewall photodetector at least a portion of the incident light including the second wavelength passed by the first sidewall photodetector.

2. The photonic device as in claim 1 , wherein the first i-layer semiconductor has a different lattice constant than that of the substrate semiconductor film.

3. The photonic device as in claim 2 , wherein the first i-layer semiconductor film has a narrower band gap than the substrate semiconductor film and wherein second light wavelength is greater than the first.

4. The photonic device as in claim 3 , wherein the substrate semiconductor film comprises predominantly silicon lattice atoms and wherein the first i-layer semiconductor film comprises a silicon germanium alloy with at least 10 at. % silicon.

5. The photonic device as in claim 2 , wherein the photodetector area on the trench sidewall is at least 300 μm 2 and film thickness of the first i-layer semiconductor film is between approximately 1.5 μm and approximately 3.0 μm.

6. The photonic device as in claim 1 , wherein the substrate semiconductor film is substantially silicon, the first i-layer semiconductor film comprises a silicon germanium alloy having a greater silicon content than does the second i-layer semiconductor film, and wherein the first i-layer semiconductor film has substantially the same film thickness as the second i-layer semiconductor film.

7. The photonic device as in claim 6 , wherein the silicon concentration profile in the first i-layer semiconductor is a non-linear function of the first i-layer semiconductor film thickness and wherein the second i-layer semiconductor is substantially pure germanium.

8. The photonic device as in claim 1 , further comprising a reflector layer over the second p-i-n film stack to reflect the second light wavelength back to the second p-i-n film stack.

9. A system comprising:

the photonic device as in claim 1 ; and

an optical demux optically coupled downstream of the first sidewall photodetector.

10. A method of forming a photonic device, the method comprising:

etching a substrate semiconductor film to form an optical waveguide in the substrate semiconductor film having a substantially vertical first trench sidewall optically coupled by the waveguide to a second trench sidewall;

forming a first p-i-n film stack over the first trench sidewall, wherein the first p-i-n film stack comprises a first i-layer semiconductor film having a band gap to absorb at least a portion of light having a first wavelength incident to the first trench sidewall and to pass at least a portion of the incident light having a second wavelength into the optical waveguide;

forming a first pair of electrodes coupled to a p-type and a n-type layer of the first p-i-n film stack to form a first photodetector having a majority of a detector area on the first trench sidewall;

forming a second p-i-n film stack over the second trench sidewall and forming a second pair of electrodes coupled to the second p-i-n film stack to form a second photodetector on the second trench sidewall, wherein the second p-i-n film stack comprises a second i-layer semiconductor film having a band gap different than that of the first i-layer semiconductor film to absorb at least a portion of light having the second wavelength transmitted from the first p-i-n film stack by the optical waveguide.

11. The method as in claim 10 , wherein forming the first p-i-n film stack further comprises:

forming a first doped semiconductor layer of a first conductivity type over the first trench sidewall;

epitaxially growing a first i-layer semiconductor film on the doped semiconductor layer, the first i-layer semiconductor film having a different lattice constant than that of the substrate semiconductor film; and

forming a second doped semiconductor layer of a second conductivity type, complementary to the first, over the first i-layer semiconductor film.

12. The method as in claim 10 ,

wherein the forming of the second p-i-n film stack includes epitaxially growing a second i-layer semiconductor over the second trench sidewall.

13. The method as in claim 12 wherein forming the second p-i-n stack further comprises:

forming the first doped semiconductor layer over the second trench sidewall at substantially the same time the first doped semiconductor layer is formed on the first trench sidewall; and

epitaxially growing the second i-layer semiconductor on the first doped semiconductor layer at substantially the same time the first i-layer semiconductor film is epitaxially grown.

14. The method as in claim 12 , wherein forming the first p-i-n stack further comprises:

performing a high angle implant with the first trench sidewall exposed to the implant species flux to implant a species into the first i-layer semiconductor film while the second trench sidewall is shadowed from the implant species flux to prevent implantation of the species into the second i-layer semiconductor film.

15. The method as in claim 14 , further comprising performing a thermal anneal activating the implant species to modify the band gap of the first i-layer semiconductor film relative to the second i-layer semiconductor film.

16. The method as in claim 13 , wherein forming the first doped layer further comprises:

epitaxially growing a silicon germanium alloy having a graded or constant silicon concentration that is at least 60 at. %.

17. A photonic device, comprising:

an optical waveguide comprising a crystalline semiconductor;

a first photodetector disposed at a first end of the optical waveguide, wherein the first photodetector includes a first p-i-n film stack disposed over a first sidewall the waveguide, wherein the first p-i-n film stack comprises a first i-layer semiconductor film having a band gap to absorb at least a portion of light incident to the first sidewall having a first wavelength and to pass at least a portion of the incident light having a second wavelength into the waveguide; and

a second sidewall photodetector disposed at a second end of the waveguide, wherein the second photodetector includes a second p-i-n film stack disposed over a second sidewall of the waveguide, wherein the second p-i-n film stack comprises a second i-layer semiconductor film having a band gap different than that of the first i-layer semiconductor film to absorb at least a portion of light having the second wavelength transmitted from the first photodetector by the waveguide.

18. The photonic device of claim 17 , wherein the semiconductor is substantially silicon, the first i-layer semiconductor film comprises a silicon germanium alloy having a greater silicon content than does the second i-layer semiconductor film.

19. The photonic device as in claim 18 , wherein a silicon concentration profile in the first i-layer semiconductor is a non-linear function of the first i-layer semiconductor film thickness and wherein the second i-layer semiconductor is substantially pure germanium.