Photonics device and CMOS device having a common gate

1. A semiconductor chip having a photonics device and a CMOS device on the same semiconductor chip comprising:

a photonics device portion and a CMOS device portion on a semiconductor chip;

a metal or polysilicon gate on the CMOS device portion, the metal or polysilicon gate having a gate extension that extends away from the CMOS device portion and toward the photonics device portion;

a germanium gate on the photonics device portion such that the germanium gate is coplanar with the metal or polysilicon gate, the germanium gate having a gate extension that extends away from the photonics device portion and toward the CMOS device portion, the germanium gate extension and metal or polysilicon gate extension joined together at a juncture to form a common gate wherein the juncture is not in contact with the photonics device portion and the juncture is not in contact with the CMOS device portion;

spacers formed on the germanium gate and the metal or polysilicon gate; and

nitride encapsulation formed on the germanium gate.

2. The semiconductor chip of claim 1 wherein the respective joined gate extensions that form a common gate between the photonics device portion and CMOS device portion are coplanar.

3. The semiconductor chip of claim 1 where the semiconductor chip comprises a semiconductor on insulator structure.

4. The semiconductor chip of claim 1 wherein the nitride encapsulation is only formed on the germanium gate.

5. The semiconductor chip of claim 1 wherein the spacers comprise first and second spacers formed on the germanium gate and the metal or polysilicon gate.

6. The semiconductor chip of claim 1 further comprising an isolation region between the photonics device portion and the CMOS device portion such that the common gate is on the isolation region.

7. A semiconductor chip having a photonics device and a CMOS device on the same semiconductor chip comprising:

a photonics device portion and a CMOS device portion on a semiconductor chip;

a metal or polysilicon gate on the CMOS device portion, the metal or polysilicon gate having a gate extension that extends toward the photonics device portion;

a germanium gate on the photonics device portion such that the germanium gate is coplanar with the metal or polysilicon gate, the germanium gate having a gate extension that extends toward the CMOS device portion, the germanium gate extension and metal or polysilicon gate extension joined together to form a common gate;

a bonding layer between the germanium gate extension and metal or polysilicon gate extension;

spacers formed on the germanium gate and the metal or polysilicon gate; and

nitride encapsulation formed on the germanium gate.

8. The semiconductor chip of claim 7 wherein the bonding layer is an oxynitride.

9. The semiconductor chip of claim 7 wherein the bonding layer has a thickness of about 10 angstroms.

10. A semiconductor chip having a photonics device and a CMOS device on the same semiconductor chip comprising:

a photonics device portion and a CMOS device portion on a semiconductor chip;

a metal or polysilicon gate on the CMOS device portion, the metal or polysilicon gate having a gate extension that extends toward the photonics device portion;

a germanium gate on the photonics device portion such that the germanium gate is coplanar with the metal or polysilicon gate, the germanium gate having a gate extension that extends toward the CMOS device portion, the germanium gate extension and metal or polysilicon gate extension joined together at a juncture to form a common gate;

nitride encapsulation formed only on the germanium gate; and

an isolation region between the photonics device portion and the CMOS device portion such that the juncture of the common gate is on the isolation region.

11. The semiconductor chip of claim 10 wherein the respective joined gate extensions that form a common gate between the photonics device portion and CMOS device portion are coplanar.

12. The semiconductor chip of claim 10 where the semiconductor chip comprises a semiconductor on insulator structure.

13. The semiconductor chip of claim 10 further comprising first and second spacers formed on the germanium gate and the metal or polysilicon gate.

14. A semiconductor chip having a photonics device and a CMOS device on the same semiconductor chip comprising:

a photonics device portion and a CMOS device portion on a semiconductor chip;

a metal or polysilicon gate on the CMOS device portion, the metal or polysilicon gate having a gate extension that extends toward the photonics device portion;

a germanium gate on the photonics device portion such that the germanium gate is coplanar with the metal or polysilicon gate, the germanium gate having a gate extension that extends toward the CMOS device portion, the germanium gate extension and metal or polysilicon gate extension joined together to form a common gate;

a bonding layer between the germanium gate extension and metal or polysilicon gate extension;

nitride encapsulation formed only on the germanium gate; and

an isolation region between the photonics device portion and the CMOS device portion such that the common gate is on the isolation region.

15. The semiconductor chip of claim 14 wherein the bonding layer is an oxynitride.

16. The semiconductor chip of claim 14 wherein the bonding layer has a thickness of about 10 angstroms.