Compound solar and manufacturing method thereof

Abstract

On a surface of a GaAs substrate, layers to be a top cell are formed by epitaxial growth. On the top cell, layers to be a bottom cell are formed. Thereafter, on a surface of the bottom cell, a back surface electrode is formed. Thereafter, a glass plate is adhered to the back surface electrode by wax. Then, the GaAs substrate supported by the glass plate is dipped in an alkali solution, whereby the GaAs substrate is removed. Thereafter, a surface electrode is formed on the top cell. Finally the glass plate is separated from the back surface electrode. In this manner, a compound solar battery that improves efficiency of conversion to electric energy can be obtained.

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         21 . A method of manufacturing a compound solar battery, comprising the steps of:
 forming a layer to be a first cell having a first band gap on a surface of a semiconductor substrate by epitaxial growth,   forming a layer to be a tunnel junction on said layer to be the first cell by epitaxial growth,   forming a layer to be a second cell having a second band gap lower than said first band gap, on said layer to be the tunnel junction,   forming a first electrode portion having a prescribed thickness to support said layer to be the first cell and said layer to be the second cell, directly on said layer to be the second cell,   separating said layer to be the first cell from said semiconductor substrate, and   forming a second electrode portion on a surface of said layer to be the first cell, exposed by separation from said semiconductor substrate.   
     
     
         22 . The method of manufacturing a compound solar battery according to  claim 21 , further comprising the steps of:
 between said step of forming a layer to be a tunnel junction and said step of forming a layer to be a second cell,   forming a layer to be a third cell having a third band gap lower than said first band gap and higher than said second band gap, on said layer to be the tunnel junction, and   forming a layer to be another tunnel junction on said layer to be the third cell by epitaxial growth,   wherein, in said step of forming a layer to be a second cell, said layer to be the second cell is formed on said layer to be another tunnel junction.   
     
     
         23 . The method of manufacturing a compound solar battery according to  claim 22 , wherein
 a compound semiconductor substrate is employed as said semiconductor substrate,   said layer to be the first cell, said layer to be the second cell, and said layer to be the third cell are compound semiconductors.   
     
     
         24 . The method of manufacturing a compound solar battery according to  claim 22 , wherein a lattice constant of each of said layer to be the first cell and said layer to be the third cell takes a value identical to the lattice constant of said semiconductor substrate. 
     
     
         25 . The method of manufacturing a compound solar battery according to  claim 21 , wherein
 a compound semiconductor substrate is employed as said semiconductor substrate, and   said layer to be the first cell and said layer to be the second cell are compound semiconductors.   
     
     
         26 . The method of manufacturing a compound solar battery according to  claim 21 , wherein a lattice constant of each of said layer to be the first cell and said layer to be the second cell takes a value identical to the lattice constant of said semiconductor substrate. 
     
     
         27 . The method of manufacturing a compound solar battery according to  claim 21 , further comprising the step of forming a prescribed intermediate layer by epitaxial growth between said layer to be the first cell and said semiconductor substrate,
 wherein said step of separating said layer to be the first cell from said semiconductor substrate includes the step of removing said semiconductor substrate by etching and further removing said intermediate layer.   
     
     
         28 . The method of manufacturing a compound solar battery according to  claim 21 , further comprising the step of forming a prescribed intermediate layer by epitaxial growth between said layer to be the first cell and said semiconductor substrate,
 wherein said step of separating said layer to be the first cell from said semiconductor substrate includes the step of removing said intermediate layer by etching to detach said semiconductor substrate.