Betavoltaic cell

• US 20070080605A1
• Filed: 08/24/2006
• Published: 04/12/2007
• Est. Priority Date: 08/25/2005
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Spencer, Michael, Chandrashekhar, MVS, Thomas, Christopher
• Granted Patent: US 7,663,288 B2
• Time in Patent Office: Days
• US Class Current: 310/303
• CPC Class Codes: G21H 1/02 Cells charged directly by beta radiation

Abstract

High aspect ratio micromachined structures in semiconductors are used to improve power density in Betavoltaic cells by providing large surface areas in a small volume. A radioactive beta-emitting material may be placed within gaps between the structures to provide fuel for a cell. The pillars may be formed of SiC. In one embodiment, SiC pillars are formed of n-type SiC. P type dopant, such as boron is obtained by annealing a borosilicate glass boron source formed on the SiC. The glass is then removed. In further embodiments, a dopant may be implanted, coated by glass, and then annealed. The doping results in shallow planar junctions in SiC.

Claims

1. A Betavoltaic cell comprising:

a substrate;

structures formed of semiconductor having voids, wherein the structures comprise shallow p-n junctions; and

electrical contacts coupled to the p-n junctions.

2. The Betavoltaic cell of claim 1 and further comprising a beta radiation source in the voids.

3. The Betavoltaic cell of claim 2 wherein the beta radiation source comprises Ni-63 or tritium (H-3).

4. The Betavoltaic cell of claim 1 wherein the structures are formed of high aspect ratio SiC or SiC⁴.

5. The Betavoltaic cell of claim 1 wherein the aspect ratio of the structures is at least approximately 10:

1.

6. The Betavoltaic cell of claim 1 wherein the structures comprise pillars.

7. The Betavoltaic cell of claim 6 wherein the pillars are formed of n doped semiconductor with a p doped exterior portion.

8. The Betavoltaic cell of claim 1 wherein the structures comprise pores.

9. A Betavoltaic cell comprising:

a SiC substrate;

high aspect ratio pillars supported by the substrate having voids between the pillars;

shallow pn junctions formed on the pillars;

cathode contacts formed on the pillars;

an anode contact formed on a back side of the substrate; and

a beta radiation fuel disposed in the voids.

10. A method of doping SiC comprising:

forming a layer of dopant containing glass on an SiC surface;

annealing the dopant containing glass to diffuse boron into the SiC; and

removing the dopant containing glass.

11. The method of claim 10 wherein the glass comprises borosilicate glass.

12. The method of claim 11 wherein the layer of borosilicate glass is formed by deposition or is spun onto the SiC.

13. The method of claim 11 wherein the layer of borosilicate glass is formed by plasma enhanced chemical vapor deposition.

14. The method of claim 10 wherein the annealing temperature is between approximately greater than 1300°

C. to approximately 1800°

C.

15. The method of claim 10 wherein the annealing is performed in a vacuum.

16. The method of claim 10 wherein the borosilicate glass is removed by immersion in hydrofluoric acid or plasma etch.

17. The method of claim 10 wherein the boron containing material comprises a boron containing ceramic.

18. The method of claim 10 wherein the SiC surface comprises high aspect ratio n-doped structures.

19. A method of doping SiC, the method comprising:

implanting a dopant into the SiC;

depositing a glass protective layer onto the SiC;

annealing to activate the dopant; and

removing the glass.