Stepped optical bridge for connecting semiconductor waveguides

1. A photonic device comprising:

a semiconductor wafer comprising:

a base layer;

a first insulating layer disposed over a surface of the base layer;

a device layer disposed over the first insulating layer; and

a waveguide formed in the device layer;

wherein the semiconductor wafer comprises walls defining a recess in the device layer and the first insulating layer, the recess exposing a portion of the surface of the base layer and an end of the waveguide; and

wherein the end of the waveguide comprises a first step having a first length and a first height, the first height being less than a thickness of the waveguide;

a semiconductor chip bonded to the surface of the base layer of the semiconductor wafer, wherein:

the semiconductor chip comprises an active region;

a facet of the active region is exposed at a sidewall of the semiconductor chip; and

there is a gap between the sidewall of the semiconductor chip and one of the walls of the semiconductor wafer defining the recess; and

a waveguide coupler disposed in the gap, the waveguide coupler comprising:

a second insulating layer disposed over the surface of the base layer of the semiconductor wafer; and

an optical bridge disposed over the second insulating layer, wherein:

the optical bridge has a first end and a second end opposing the first end;

the first end of the optical bridge is interfaced with the facet of the active region; and

the second end of the optical bridge has a second step having a second length and a second height, the second height being less than a thickness of the optical bridge, and the second step is disposed over the first step of the waveguide.

2. The photonic device of claim 1 , wherein the first height of the first step ranges from about 5% to about 95% of the thickness of the waveguide.

3. The photonic device of claim 2 , wherein the first height of the first step ranges from about 10% to about 85%, or from about 20% to about 75%, or from about 30% to about 65%, or from about 40% to about 55%, of the thickness of the waveguide.

4. The photonic device of claim 1 , wherein the first length of the first step ranges from about 0.1 μm to about 50 μm.

5. The photonic device of claim 4 , wherein the first length of the first step ranges from about 0.5 μm to about 50 μm, or from about 1 μm to about 50 μm, or from about 5 μm to about 50 μm.

6. The photonic device of claim 1 , wherein the base layer of the semiconductor wafer comprises silicon.

7. The photonic device of claim 6 , wherein the semiconductor chip comprises a III-V material.

8. The photonic device of claim 7 , wherein the active region comprises a multiple-quantum-well (MQW) structure.

9. The photonic device of claim 1 , further comprising:

a third insulating layer disposed over the waveguide.

10. The photonic device of claim 9 , wherein:

the base layer of the semiconductor wafer comprises silicon;

the waveguide comprises crystalline silicon; and

the first insulating layer, the second insulating layer, and the third insulating layer comprise silicon oxide.

11. The photonic device of claim 10 , wherein the optical bridge comprises amorphous silicon.

12. The photonic device of claim 1 , wherein the waveguide has a first refractive index, and the optical bridge has a second refractive index different from the first refractive index.

13. A method for fabricating a photonic device, the method comprising:

providing a semiconductor wafer, the semiconductor wafer comprising:

a base layer;

a first insulating layer disposed over a surface of the base layer;

a device layer disposed over the first insulating layer; and

a waveguide formed in the device layer;

performing etching to form a recess in the device layer and the first insulating layer, wherein:

the recess exposes a portion of the surface of the base layer; and

the recess has a sidewall exposing an end of the waveguide;

bonding a semiconductor chip to the exposed portion of the surface of the base layer, wherein:

the semiconductor chip comprises an active region;

a facet of the active region is exposed at a sidewall of the semiconductor chip; and

there is a gap between the sidewall of the semiconductor chip and the sidewall of the recess;

forming a second insulating layer in the gap;

performing etching to remove a portion of the waveguide to form a first step at the end of the waveguide; and

forming an optical bridge over the second insulating layer, wherein:

the optical bridge has a first end and a second end opposing the first end;

the first end of the optical bridge is interfaced with the facet of the active region; and

the second end of the optical bridge has a second step disposed over the first step at the end of the waveguide.

14. The method of claim 13 , wherein the first step has a height ranging from about 5% to about 95% of the thickness of the waveguide.

15. The method of claim 14 , wherein the first step has a height ranging from about 10% to about 85%, or from about 20% to about 75%, or from about 30% to about 65%, or from about 40% to about 55%, of the thickness of the waveguide.

16. The method of claim 13 , wherein the first step has a length ranging from about 0.1 μm to about 50 μm.

17. The method of claim 16 , wherein the first step has a length ranging from about 0.5 μm to about 50 μm, or from about 1 μm to about 50 μm, or from about 5 μm to about 50 μm.

18. The method of claim 13 , wherein the base layer of the semiconductor wafer comprises silicon.

19. The method of claim 18 , wherein the semiconductor chip comprises a III-V material.

20. The method of claim 19 , wherein the active region comprises a multiple-quantum-well (MQW) structure.