Patent Number: 
Section: claims

1. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed of semiconductor; andelectrical contacts coupled to the p-n junctions, wherein the contacts are adapted to minimize beta radiation backscatter losses. 2. The Betavoltaic cell of claim 1 and further comprising a beta radiation source. 3. The Betavoltaic cell of claim 2 wherein the beta radiation source comprises Ni-63 or tritium (H-3) or both. 4. The Betavoltaic cell of claim 1 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 5. The Betavoltaic cell of claim 2 wherein the radiation source comprises beta radiation producing particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 6. The Betavoltaic cell of claim 1 wherein the surface of the semiconductor is passivated. 7. The Betavoltaic cell of claim 1 wherein the p-n junctions are formed from n doped semiconductor disposed underneath p doped semiconductor or a p doped semiconductor disposed underneath n doped semiconductor. 8. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed from semiconductor;cathode or anode contacts coupled to the p-n junctions wherein contact areas are adapted to minimize beta radiation backscatter losses;an anode or cathode contact formed on a back side of the substrate; anda beta radiation fuel. 9. The Betavoltaic cell of claim 8 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 10. The Betavoltaic cell of claim 8 wherein the radiation fuel comprises beta radiation particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 11. The Betavoltaic cell of claim 8, wherein the surface of the semiconductor is passivated. 12. The Betavoltaic cell of claim 8 wherein the beta radiation fuel comprises Ni-63, tritium (H-3) or both. 13. The Betavoltaic cell of claim 8 wherein the p-n junction is formed from n doped semiconductor disposed underneath p doped semiconductor or p doped semiconductor disposed underneath n doped semiconductor. 14. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed of semiconductor,a void proximal to the p-n junctions;cathode or anode contacts coupled to the p-n junctions, wherein the contacts have an area adapted to minimize beta radiation backscatter losses;an anode or cathode contact formed on a back side of the substrate; anda cap formed of semiconductor. 15. The Betavoltaic cell of claim 14 and further comprising a beta radiation source. 16. The Betavoltaic cell of claim 15 wherein the beta radiation source comprises Ni-63 or tritium (H-3) or both. 17. The Betavoltaic cell of claim 14 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 18. The Betavoltaic cell of claim 14 wherein the radiation source comprises beta radiation producing particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 19. The Betavoltaic cell of claim 14 wherein the surface of the semiconductor is passivated. 20. The Betavoltaic cell of claim 14 wherein the p-n junction is formed from n doped semiconductor disposed underneath p doped semiconductor or p doped semiconductor disposed underneath n doped semiconductor. 21. A Betavoltaic cell comprising:a semiconductor substrate having a passivated surface;p-n junctions formed of semiconductor supported by the semiconductor substrate, wherein an upper layer of the junctions comprise a passivated surface;a void proximal to the p-n junctions adapted to hold beta radiation particles;first contacts coupled to the p-n junctions, wherein the first contacts occupy less than about 1% of the area of the p-n junctions to minimize beta radiation backscatter losses;a second contact formed on a back side of the substrate; anda cap formed of semiconductor positioned to cover the void. 22. The Betavoltaic cell of claim 21 wherein the first contacts comprise an annealed metal.