Lapped substrate for enhanced backsurface reflectivity in a thermophotovoltaic energy conversion system

Abstract

A method for fabricating a thermophotovoltaic energy conversion cell including a thin semiconductor wafer substrate (10) having a thickness (β) calculated to decrease the free carrier absorption on a heavily doped substrate; wherein the top surface of the semiconductor wafer substrate is provided with a thermophotovoltaic device (11), a metallized grid (12) and optionally an antireflective (AR) overcoating; and, the bottom surface (10') of the semiconductor wafer substrate (10) is provided with a highly reflecting coating which may comprise a metal coating (14) or a combined dielectric/metal coating (17).

What is claimed is: 
     
       1. A method of fabricating a thermophotovoltaic energy conversion cell in order to provide spectral control and improve efficiency, wherein the method comprises the following steps: a) forming a thermophotovoltaic device on the top surface of a doped semiconductor wafer substrate followed by the formation of a metallized grid on top of said thermophotovoltaic device; wherein said thermophotovoltaic device comprises material selected from InGaAsSb, InGaAs, InGaSb, and InAsPSb, and   wherein said doped semiconductor wafer substrate comprises material selected from GaSb, InP, and InAs,     b) subjecting said doped semiconductor wafer substrate, having an initial thickness "Δ", to a lapping operation to remove an excess thickness "β" so that said substrate has a finished thickness "α", wherein "β" is 3 to 5 mils, and   c) forming a reflecting coating on the bottom surface of said substrate.   
     
     
       2. The method as in claim 1 wherein step b) precedes step a). 
     
     
       3. The method as in claim 1; wherein, said lapping operation involves a mechanical lapping process. 
     
     
       4. The method as in claim 3; wherein, said mechanical lapping process is followed by a chemical etching process. 
     
     
       5. The method as in claim 1; wherein, said lapping operation involves a chemical etching process. 
     
     
       6. The method as in claim 1; wherein, step c) includes the vapor deposition of a reflecting metal coating on the bottom surface of said semiconductor wafer substrate. 
     
     
       7. The method as in claim 1; wherein, the reflecting coating comprises a combination dielectric/metal reflector. 
     
     
       8. The method as in claim 1 further including the step of: d) depositing an antireflective coating on top of both the thermophotovoltaic device and the metallized grid.   
     
     
       9. The method as in claim 7; wherein, the combination dielectric/metal reflector is formed by the chemical vapor deposition of a dielectric layer on the bottom surface of the semiconductor wafer substrate, followed by utilizing photolithography to pattern a photoresist film on the dielectric, then the chemical etching of the dielectric layer and the vapor deposition of a metal contact reflector onto the etched dielectric layer. 
     
     
       10. The method as in claim 6 further comprising the step of: e) operatively engaging the bottom surface of the reflecting coating to a module substrate.   
     
     
       11. The method as in claim 2; wherein, said lapping operation involves a mechanical lapping process. 
     
     
       12. The method as in claim 2; wherein, said lapping operation involves a chemical etching process. 
     
     
       13. The method as in claim 2; wherein, step c) includes the vapor deposition of a reflecting metal coating on the bottom surface of said semiconductor wafer substrate. 
     
     
       14. The method as in claim 2; wherein, the reflecting coating comprises a combination dielectric/metal reflector. 
     
     
       15. The method as in claim 7 further comprising the step of: e) operatively engaging the bottom surface of the reflecting coating to a module substrate.   
     
     
       16. A thermophotovoltaic energy cell comprising: a thin semiconductor wafer substrate having a top surface, a bottom surface, and a selected thickness "β"; wherein "β" is 3 to 5 mils, said thickness being optimized to decrease the free carrier absorption on a doped substrate;   a thermophotovoltaic device on the top surface of said semiconductor wafer substrate, a metallized grid on said thermophotovoltaic layer; and,   a reflecting layer on the bottom of said semiconductor wafer substrate.   
     
     
       17. The thermophotovoltaic energy cell as in claim 16; wherein, said reflecting layer comprises a highly reflective metal. 
     
     
       18. The thermophotovoltaic energy cell as in claim 16; wherein, said reflecting layer comprises a combination dielectric/metal reflector. 
     
     
       19. The thermophotovoltaic energy cell as in claim 16 further including: f) an antireflective overcoating layer on both said metallized grid and on said thermophotovoltaic device.   
     
     
       20. The thermophotovoltaic energy cell as in claim 16; wherein, said reflective metal is chosen from a class including silver, gold, copper and platinum. 
     
     
       21. The thermophotovoltaic energy cell as in claim 16; wherein the substrate is fabricated from a class of materials which includes GaSb, InP and InAs. 
     
     
       22. The thermophotovoltaic energy cell as in claim 16; wherein the thermophotovoltaic device is fabricated from a class of materials which includes InGaAsSb InGaAs, InGaSb, InAsPSb. 
     
     
       23. The thermophotovoltaic energy cell as in claim 18; wherein, the combination dielectric/metal reflector is fabricated from a class of dielectric materials which includes silicon dioxide, silicon nitride, silicon monoxide. 
     
     
       24. The thermophotovoltaic energy cell as in claim 23; wherein, the combination dielectric/metal reflector is fabricated from a class of metals which includes gold, silver, copper, platinum. 
     
     
       25. The method as in claim 11; wherein, said mechanical lapping process is followed by a chemical etching process. 
     
     
       26. A thermophotovoltaic energy cell made by the process of claim 1, said cell comprising: a thin heavily doped semiconductor wafer substrate having a top surface, a bottom surface, and a selected finished thickness "β"; wherein "β" is 3 to 5 mils;   a thermophotovoltaic device on the top surface of said semiconductor wafer substrate,   a metallized grid on top of said thermophotovoltaic device; and,   a reflecting coating on the bottom surface of said semiconductor wafer substrate.