Germanium-on-silicon laser in CMOS technology

Patent metadata

Field	Value
Publication number	US-11329455-B2
Application number	US-202016867666-A
Country	US
Kind code	B2
Filing date	May 6, 2020
Priority date	Mar 6, 2015
Publication date	May 10, 2022
Grant date	May 10, 2022

Abstract

A germanium waveguide is formed from a P-type silicon substrate that is coated with a heavily-doped N-type germanium layer and a first N-type doped silicon layer. Trenches are etched into the silicon substrate to form a stack of a substrate strip, a germanium strip, and a first silicon strip. This structure is then coated with a silicon nitride layer.

First claim

The invention claimed is:

1. A method of forming a germanium waveguide, comprising:
forming a N-type doped germanium strip in a silicon substrate;
forming a P-type doped silicon strip on a first side of the N-type doped germanium strip;
forming an N-type doped silicon strip on a second side of the N-type doped germanium strip opposite said first side;
etching so that the N-type doped germanium strip and adjacent portions of the P-type and N-type doped silicon strips are raised with respect to a substrate surface; and
coating the N-type doped germanium strip and the adjacent portions as well as a structure adjacent thereto with a silicon nitride layer.

2. The method of claim 1 , wherein etching comprises performing an etch which:
selectively removes a portion of the P-type doped silicon strip and an adjacent portion of the silicon substrate to leave the adjacent portion of the P-type doped silicon strip raised above the substrate surface and leave a recessed portion of the P-type doped silicon strip coplanar with the substrate surface; and
selectively removes a portion of the N-type doped silicon strip and an adjacent portion of the silicon substrate to leave the adjacent portion of the N-type doped silicon strip raised above the substrate surface and leave a recessed portion of the N-type doped silicon strip coplanar with the substrate surface.

3. The method of claim 2 , wherein a bottom of the N-type doped germanium strip is coplanar with the substrate surface.

4. The method of claim 2 , wherein coating comprises depositing the silicon nitride layer on the substrate surface, the recessed portion of the P-type doped silicon strip and the recessed portion of the N-type doped silicon strip.

5. The method of claim 4 , further comprising:
forming a first opening extending through the silicon nitride layer to expose an upper surface of the recessed portion of the P-type doped silicon strip; and
forming a second opening extending through the silicon nitride layer to expose an upper surface of the recessed portion of the N-type doped silicon strip.

6. The method of claim 5 , further comprising:
forming a first metal contact in said first opening to electrically connect to the recessed portion of the P-type doped silicon strip; and
forming a second metal contact in said second opening to electrically connect to the recessed portion of the N-type doped silicon strip.

7. The method of claim 6 , wherein the first metal contact and second metal contact each extend partially on a top surface of the silicon nitride layer outside of the first opening and second opening, respectively.

8. The method of claim 6 , wherein forming the first and second metal contacts comprises leaving portions of the first legs of the P-type and N-type doped silicon strips in said first and second openings, respectively, uncovered by the first and second metal contacts, respectively.

9. A germanium waveguide, comprising:
a silicon substrate,
a N-type doped germanium strip on said silicon substrate;
a P-type doped silicon strip on the silicon substrate adjacent a first side of the N-type doped germanium strip;
an N-type doped silicon strip on the silicon substrate adjacent a second side of the N-type doped germanium strip opposite said first side; and
a silicon nitride layer coating the N-type doped germanium strip and the silicon strips.

10. The waveguide of claim 9 :
wherein the P-type doped silicon strip has a shape in a cross-section extending perpendicularly through the silicon substrate of an L with a first leg extending parallel to and coplanar with a top surface of the silicon substrate and a second leg extending perpendicular to the coplanar top surface of the silicon substrate and positioned in contact with the first side of the N-type doped germanium strip; and
wherein the N-type doped silicon strip has a shape in the cross-section extending perpendicularly through the silicon substrate of an L with a first leg extending parallel to and coplanar with the top surface of the silicon substrate and a second leg extending perpendicular to the coplanar top surface of the silicon substrate and positioned in contact with the second side of the N-type doped germanium strip.

11. The waveguide of claim 10 , wherein a top surface of each first leg is coplanar with the top surface of the silicon substrate.

12. The waveguide of claim 10 , wherein the silicon nitride layer coats a top surface of each first leg.

13. The waveguide of claim 12 , further comprising:
a first opening extending through the silicon nitride layer to an upper surface of the first leg of the P-type doped silicon strip; and
a second opening extending through the silicon nitride layer to an upper surface of the first leg of the N-type doped silicon strip.

14. The waveguide of claim 13 , further comprising:
a first metal contact in said first opening to electrically connect to the first leg of the P-type doped silicon strip; and
a second metal contact in said second opening to electrically connect to the first leg of the N-type doped silicon strip.

15. The waveguide of claim 14 , wherein the first metal contact and second metal contact each extend partially on a top surface of the silicon nitride layer outside of the first opening and second opening, respectively.

16. The waveguide of claim 14 , wherein portions of the first legs of the P-type and N-type doped silicon strips in said first and second openings, respectively, are not covered by the first and second metal contacts, respectively.

Assignees

• St Microelectronics Crolles 2 Sas

Inventors

• Prost Mathias
• El Kurdi Moustafa
• Boucaud Philippe
• Boeuf Frederic

Classifications

• H01S5/3086

  doping of the active layer · CPC title

• G02B2006/12121

  Laser · CPC title

• H01S5/0424

  lateral current injection · CPC title

• H01S5/1003

  Waveguide having a modified shape along the axis, e.g. branched, curved, tapered, voids · CPC title

• G02B6/136

  by etching · CPC title