Co-integration of photonic devices on a silicon photonics platform

1. A method comprising:

providing a planarized silicon-based photonics substrate comprising a silicon waveguide structure;

depositing a dielectric layer over the planarized silicon-based photonics substrate;

selectively etching the dielectric layer, thereby exposing at least a portion of the silicon waveguide structure;

selectively etching the exposed portion of the silicon waveguide structure to form a step-like template;

using the silicon waveguide structure as a seed layer to selectively grow in the step-like template a germanium layer that extends above the dielectric layer; and

planarizing the germanium layer to form a planarized germanium layer, wherein the planarized germanium layer does not extend above the dielectric layer and, as a result of the step-like template, has an inverted rib shape,

wherein the inverted rib shape comprises a lower portion and an upper portion that is wider than the lower portion, wherein the lower portion comprises an optically-active region, and wherein the upper portion comprises laterally-overhanging portions that extend laterally above and beyond either side of the optically active region lower portion.

2. The method of claim 1 , wherein the dielectric layer comprises an oxide layer.

3. The method of claim 2 , wherein the oxide layer comprises a SiO 2 layer.

4. The method of claim 1 , further comprising, before planarizing the germanium layer, annealing the germanium layer.

5. The method of claim 1 , wherein the planarized germanium layer has a thickness between about 100 nm and about 500 nm.

6. The method of claim 1 , wherein planarizing the germanium layer comprises using a chemical mechanical polish to planarize the germanium layer.

7. The method of claim 1 , further comprising:

forming a germanium photodetector structure comprising the planarized germanium layer.

8. The method of claim 1 , wherein the optically-active region has a thickness between about 250 nm and about 300 nm.

9. The method of claim 1 , further comprising providing metal contacts in electrical contact with the laterally-overhanging portions, wherein the metal contacts and the optically-active region are separated by a lateral distance of at least 50 nm.

10. A method comprising:

providing a planarized silicon-based photonics substrate comprising a first silicon waveguide structure and a second silicon waveguide structure;

depositing a dielectric layer over the planarized silicon-based photonics substrate;

selectively etching the dielectric layer, thereby exposing at least a portion of the first silicon waveguide structure;

selectively etching the exposed portion of the first silicon waveguide structure to form a template;

using the first silicon waveguide structure as a seed layer to selectively grow in the template a germanium layer that extends above the dielectric layer;

planarizing the germanium layer to form a planarized germanium layer, wherein the planarized germanium layer does not extend above the dielectric layer;

forming a germanium photodetector structure comprising the first planarized germanium layer;

bonding a III-V layer to the dielectric layer at a distance of less than about 100 nm from the second silicon waveguide structure; and

integrating a hybrid laser structure with the planarized silicon-based photonics substrate, wherein the hybrid laser structure comprises the III-V layer.

11. The method of claim 10 , wherein as a result of the first template, the first planarized germanium layer has an inverted rib shape.

12. The method of claim 10 , further comprising, in a single processing step, forming contacts to the first silicon waveguide structure, the second silicon waveguide structure, the germanium photodetector structure, and the hybrid laser structure.

13. The method of claim 1 , wherein a bottom surface of each of the laterally-overhanging portions is in contact with the dielectric layer.