Method of fabrication of a support structure for a semiconductor device
View Patent ↗A method of fabricating a semiconductor device is described. In this method, a starting substrate of sufficient thickness is selected that has the required defect density levels, which may result in an undesirable doping level. Then a semiconductor layer having a desired doping level is formed on the starting substrate. The resulting semiconductor layer has the required defect density and doping levels for the final product application. After active components, electrical conductors, and any other needed structures are formed on the semiconductor layer, the starting substrate is removed leaving a desired thickness of the semiconductor layer. In a VECSEL application, the active components can be a gain cavity, where the semiconductor layer has the necessary defect density and doping levels to maximize wall plug efficiency (WPE). In one embodiment, the doping of the semiconductor layer is not uniform. For example, a majority of the layer is doped at a low level and the remainder is doped at a much higher level. This can result in improved WPE at particular thicknesses for the higher doped material.
1. A method of fabricating a semiconductor device comprising:
selecting a starting semiconductor substrate having a first defect density and a first doping level;
forming a semiconductor layer on said starting semiconductor substrate to have a second defect density that is equal to or less than the first defect density, the semiconductor layer being doped during formation to have a second doping level that is less than the first doping level at a first surface closest to the starting semiconductor substrate;
forming active components on a second surface of said semiconductor layer, opposite to the first surface; and
removing said starting semiconductor substrate.
2. The method of claim 1 further comprising:
controlling a doping level for said semiconductor layer during formation.
3. The method of claim 2 wherein the doping level is controlled to uniformly dope the semiconductor layer at the second doping level.
4. The method of claim 2 wherein the doping level is controlled to dope a majority of the thickness of said semiconductor layer at the second doping level and dope a region of said semiconductor layer adjacent to the second surface at a third, higher doping level.
5. The method of claim 1 wherein said starting semiconductor substrate and said semiconductor layer are made from GaAs.
6. The method of claim 1 wherein said starting semiconductor substrate is made from GaAs and said semiconductor layer is made from epitaxial growth of a single crystal material.
7. The method of claim 6 wherein said semiconductor layer is made from AlGaAsP.
8. The method of claim 1 wherein said starting semiconductor substrate has a low defect density.
9. The method of claim 8 further comprising:
controlling a doping level for said semiconductor layer during formation.
10. The method of claim 9 wherein the semiconductor layer is uniformly doped at the second doping level.
11. The method of claim 8 wherein said starting semiconductor substrate and said semiconductor layer are made from GaAs.
12. The method of claim 8 wherein said starting semiconductor substrate is made from GaAs and said semiconductor layer is made from epitaxial growth of a single crystal material.
13. The method of claim 12 wherein said semiconductor layer is made from AlGaAsP.
14. The method of claim 1 wherein said forming active components includes forming an optical gain cavity on the second surface of said semiconductor layer, the optical gain cavity arranged to emit light through the semiconductor layer.
15. The method of claim 14 further comprising:
controlling a doping level for said semiconductor layer during formation.
16. The method of claim 15 wherein the doping level is controlled to uniformly dope the semiconductor layer at the second doping level.
17. The method of claim 14 wherein said starting semiconductor substrate and said semiconductor layer are made from GaAs.
18. The method of claim 14 wherein said starting semiconductor substrate is made from GaAs and said semiconductor layer is made from epitaxial growth of a single crystal material.
19. The method of claim 18 wherein said semiconductor layer is made from AlGaAsP.
20. The method of claim 14 , further comprising:
forming an optical aperture on the first surface of said semiconductor layer after removing said starting semiconductor substrate; and
disposing an external mirror/lens relative to the first surface of said semiconductor layer to create an extended optical cavity.
21. The method of claim 20 further comprising:
controlling a doping level for said semiconductor layer during formation.
22. The method of claim 21 wherein the semiconductor layer is uniformly doped at the second doping level.
23. The method of claim 22 wherein the second doping level is between 5×10 16 cm −3 and 5×10 17 cm −3 .
24. The method of claim 21 wherein the doping level is controlled to dope a majority of the thickness of said semiconductor layer at the second doping level, and dope a region of said semiconductor layer adjacent to the second surface at a third, higher doping level.
25. The method of claim 20 wherein said starting semiconductor substrate and said semiconductor layer are made from GaAs.
26. The method of claim 20 wherein said starting semiconductor substrate is made from GaAs and said semiconductor layer is are made from epitaxial growth of a single crystal material.
27. The method of claim 26 wherein said semiconductor layer is made from AlGaAsP.
28. The method of claim 20 further comprising:
forming an anti-reflecting layer on the first surface of said semiconductor layer after removing said starting semiconductor substrate, the optical aperture to be formed on the anti-reflecting layer.
29. The method of claim 14 wherein said forming active components further includes:
forming a first electrical contact on the optical gain cavity; and
forming a second electrical contact to electrically contact the second surface of the semiconductor substrate, the first and second electrical contacts being formed on a same side of the semiconductor layer.
30. The method of claim 29 further comprising:
controlling a doping level for said semiconductor layer during formation, the doping level being controlled to dope a majority of the thickness of said semiconductor layer at the second doping level and dope a region of said semiconductor layer adjacent to the second surface at a third, higher doping level.
31. The method of claim 14 further comprising:
controlling a doping level for said semiconductor layer during formation, the doping level being controlled to dope a majority of the thickness of said semiconductor layer at the second doping level and dope a region of said semiconductor layer adjacent to the second surface at a third, higher doping level.
32. The method of claim 1 further comprising:
forming an etch-stop layer on the starting semiconductor substrate prior to forming the semiconductor layer, wherein the etch-stop layer is composed of a different material than the starting semiconductor substrate and the semiconductor layer.
33. The method of claim 32 further comprising:
removing the etch-stop layer after removing the starting semiconductor substrate.
34. The method of claim 1 further comprising:
forming a first electrical contact over the active components; and
forming a second electrical contact to electrically contact the second surface of the semiconductor substrate, the first and second electrical contacts being formed on a same side of the semiconductor layer.
35. The method of claim 34 further comprising:
controlling a doping level for said semiconductor layer during formation, the doping level being controlled to uniformly dope the semiconductor layer at the second doping level.
36. The method of claim 34 further comprising:
controlling a doping level for said semiconductor layer during formation, the doping level being controlled to dope a majority of the thickness of said semiconductor layer at the second doping level and dope a region of said semiconductor layer adjacent to the second surface at a third, higher doping level.