Method and apparatus for fabricating a thin-film solar cell utilizing a hot wire chemical vapor deposition technique

1. A method for fabricating a thin film solar cell, the method comprising: forming an n-type semiconductor layer; forming a p-type semiconductor layer; forming two or more hydrogenated amorphous silicon-germanium (a-SIGe:H) intrinsic layers between the n-type semiconductor layer and the p-type semiconductor layer wherein at least one of the hydrogenated amorphous silicon-germanium (a-SiGe:H) intrinsic layers is formed using hot wire chemical vapor deposition with a filament positioned in a chamber parallel to the at least one formed layer and wherein two adjacent amorphous silicon-germanium (a-SiGe:H) intrinsic layers, each having a constant germanium to silicon percentage ratio (Ge/Si), form a step in germanium to silicon percentage ratio (Ge/Si).

2. A method as defined in claim 1 , wherein the hot wire chemical vapor deposition comprises use of a filament comprising tungsten.

3. A method as defined in claim 1 , wherein the two or more a-SiGe:H intrinsic layers comprise three intrinsic layers formed using hot wire chemical vapor deposition.

4. A method as defined in claim 1 , wherein the two or more a-SiGe:H intrinsic layers are formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of from 30 to 50 sccm, H 2 flowed at a rate of from 0 to 190 sccm, and GeH 4 flowed at rate of up to 12.5 sccm.

5. A method as defined in claim 1 , wherein the two or more a-SiGe:H intrinsic layers are formed in a chamber having a pressure from 20 to 50 mT using hot wire chemical vapor deposition including SiH 4 flowed at a rate of from 30 to 50 sccm, H 2 flowed at a rate of from 0 to 190 sccm, and GeH 4 flowed at a rate up to 12.5 sccm.

6. A method as defined in claim 1 wherein the two or more a-SiGe:H intrinsic layers comprise a second intrinsic layer and a third intrinsic layer, and the solar cell further comprises a first intrinsic layer.

7. A method as defined in claim 6 wherein the first intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm and H 2 flowed at a rate of approximately 150 sccm.

8. A method as defined in claim 6 wherein the first intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

9. A method as defined in claim 6 wherein the first intrinsic layer is formed in a chamber having a pressure of approximately 42 mT using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

10. A method as defined in claim 6 wherein the second intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 4.3 sccm, and H 2 flowed at a rate of approximately 150 sccm.

11. A method as defined in claim 6 wherein the second intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 4.3 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

12. A method as defined in claim 6 wherein the second intrinsic layer is formed in a chamber having a pressure of approximately 43 mT using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 4.3 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

13. A method as defined in claim 6 wherein the second intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 8%.

14. A method as defined in claim 6 wherein the third intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 9.5 sccm, and H 2 flowed at a rate of approximately 150 sccm.

15. A method as defined in claim 6 wherein the third intrinsic layer is formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 9.5 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

16. A method as defined in claim 6 wherein the third intrinsic layer is formed in a chamber having a pressure of approximately 45 mT using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, GeH 4 flowed at a rate of approximately 9.5 sccm, H 2 flowed at a rate of approximately 150 sccm, and a deposition time of approximately 90 seconds.

17. A method as defined in claim 6 wherein the third intrinsic layer has germanium to silicon ratio (Ge/Si) of approximately 16%.

18. A method as defined in claim 6 wherein the first, second, and third intrinsic layers are formed using hot wire chemical vapor deposition including SiH 4 flowed at a rate of approximately 50 sccm, and H 2 flowed at a rate of approximately 150 sccm.

19. A method as defined in claim 18 wherein the step in germanium to silicon percentage ratio (Ge/Si) exists between the second intrinsic layer and the third intrinsic layer where the second intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 8%, and the third intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 16%.

20. A method as defined in claim 18 wherein the first intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 0%, and wherein the step in germanium to silicon percentage ratio (Ge/Si) exists between the second intrinsic layer and the third intrinsic layer where the second intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 8%, and the third intrinsic layer has a germanium to silicon ratio (Ge/Si) of approximately 16%.

21. A method as defined in claim 18 wherein the second intrinsic layer is formed using GeH 4 flowed at a rate of approximately 4.3 sccm.

22. A method as defined in claim 18 wherein the third intrinsic layer is formed using GeH 4 flowed at a rate of approximately 9.5 sccm.

23. A method as defined in claim 18 wherein the second intrinsic layer is formed using GeH 4 flowed at a rate of approximately 4.3 sccm and the third intrinsic layer is formed using GeH 4 flowed at a rate of approximately 9.5 sccm.