Avalanche photodiode structure

1. A germanium based avalanche photodiode device, the germanium based avalanche photodiode device including:

a silicon substrate;

a buried oxide layer, above the silicon substrate;

a lower doped silicon region, above the buried oxide layer;

a silicon multiplication region, above the lower doped silicon region;

an intermediate doped silicon region, above the silicon multiplication region;

a doped germanium interface layer, above the intermediate doped silicon region;

an un-doped germanium absorption region, above the intermediate doped silicon region;

an upper doped germanium region, above the un-doped germanium absorption region;

an input silicon waveguide; a first electrode; and a second electrode,

wherein: the un-doped germanium absorption region and the upper doped germanium region form a germanium waveguide which is coupled to the input silicon waveguide,

the first electrode extends laterally to contact the lower doped silicon region, and

the second electrode extends laterally to contact the upper doped germanium region.

2. The germanium based avalanche photodiode device of claim 1 , wherein the doped germanium interface layer has a thickness between 30 nm and 200 nm.

3. The germanium based avalanche photodiode device of claim 1 , wherein the lower doped silicon region includes a part which extends away from the buried oxide layer so as to contact the first electrode.

4. The germanium based avalanche photodiode device of claim 1 , wherein the input silicon waveguide and germanium waveguide are rib waveguides.

5. The germanium based avalanche photodiode device of claim 1 , wherein the germanium waveguide has a first lateral edge, and the lower doped silicon region is coterminous in lateral extension with the first lateral edge of the germanium waveguide.

6. The germanium based avalanche photodiode device of claim 1 , wherein the germanium waveguide has a first lateral edge, and the lower doped silicon region extends laterally beyond the first lateral edge of the germanium waveguide.

7. The germanium based avalanche photodiode device of claim 1 , wherein the multiplication silicon region, the germanium waveguide, and the intermediate doped silicon region are within a cavity of a silicon-on-insulator layer.

8. The germanium based avalanche photodiode device of claim 1 , wherein the multiplication silicon region is between 50 nm and 150 nm thick.

9. The germanium based avalanche photodiode device of claim 1 , wherein the upper doped germanium region and the lower doped silicon region are heavily doped as compared to the intermediate doped silicon region.

10. The germanium based avalanche photodiode device of claim 1 , wherein the intermediate doped silicon region is doped with dopants of a same species as the upper doped germanium region.

11. The germanium based avalanche photodiode device of claim 1 , wherein a top surface of the input silicon waveguide is substantially aligned with a top surface of the germanium waveguide.

12. A method of fabricating a germanium based avalanche photodiode device, comprising:

providing a silicon substrate and an insulator layer, above which is a silicon-on-insulator layer;

etching the silicon-on-insulator layer, to form a cavity of the silicon-on-insulator layer, the bottom of which includes a first silicon layer on the insulator layer;

doping the first silicon layer to form a lower doped silicon region;

growing a second silicon layer from an upper surface of the lower doped silicon region;

doping a first part of the second silicon layer to form an intermediate doped silicon region;

epitaxially growing a germanium layer from an upper surface of the second silicon layer to form a germanium waveguide,

the growing comprising using in-situ doping to form a doped germanium interface layer on the intermediate doped silicon region;

doping a part of the germanium layer to form an upper doped germanium region; and

providing a first electrode and a second electrode, the first electrode contacting the lower doped silicon region and the second electrode contacting the upper doped germanium region.

13. The method of claim 12 , further including a step of:

after etching the silicon-on-insulator layer and before epitaxially growing the first silicon layer: disposing an insulating layer along sidewalls and the bed of the cavity.

14. The method of claim 13 , including the step of:

etching the insulating layer which is along the bed of the cavity, thereby leaving an insulating layer along the sidewalls of the cavity.

15. The method of claim 12 , including the step of doping a region of the first silicon layer.

16. The method of claim 12 , wherein the doped germanium interface layer has a thickness between 30 nm and 200 nm.

17. The method of claim 12 , including the step of:

etching a part of the germanium layer, to thereby provide a rib waveguide having one or more slab regions.

18. The method of claim 12 , including the step of:

before the doping of the part of the germanium layer:

disposing a photoresist over a part of an upper most surface of the partially fabricated germanium based avalanche photodiode device;

and after doping the part of the germanium layer:

removing the photoresist.

19. The method of claim 13 , further including a step of:

annealing the partially fabricated germanium based avalanche photodiode device.

20. The method of claim 13 , further including a step of:

disposing a cladding layer over the partially fabricated germanium based avalanche photodiode device.