Germanium enriched silicon material for making solar cells

Abstract

Techniques for the formation of silicon ingots and crystals using silicon feedstock of various grades are described. A common feature is adding a predetermined amount of germanium to the melt and performing a crystallization to incorporate germanium into the silicon lattice of respective crystalline silicon materials. Such incorporated germanium results in improvements of respective silicon material characteristics, including increased material strength and improved electrical properties. This leads to positive effects at applying such materials in solar cell manufacturing and at making modules from those solar cells.

What is claimed is: 
     
         1 . A method for forming crystalline silicon having improved mechanical and electrical characteristics, comprising the steps of:
 initiating a silicon crystallization process using a predetermined amount of a silicon feedstock material;   adding to said silicon feedstock material a predetermined quantity of germanium, wherein the quantity of germanium ranges from 5 to 50 ppmw;   generating a melt from respective silicon feedstock material and said quantity of germanium; and   performing a crystallization of said melt.   
     
     
         2 . The method of  claim 1 , further comprising the step of initiating a directional solidification silicon crystallization process using a predetermined amount of silicon feedstock material. 
     
     
         3 . The method of  claim 1 , further comprising the step of initiating a directional solidification silicon crystallization process using a predetermined amount of UMG silicon feedstock material. 
     
     
         4 . The method of  claim 1 , further comprising the step of initiating a CZ silicon crystal pulling process using an EG silicon feedstock material. 
     
     
         5 . The method of  claim 1 , further comprising the step of initiating a CZ silicon crystal pulling process using an SOG silicon feedstock material. 
     
     
         6 . The method of  claim 1 , further comprising the step of initiating an FZ silicon crystallization process using an EG silicon supply rod. 
     
     
         7 . The method of  claim 1 , wherein adding to said silicon feedstock material the quantity of germanium includes adding germanium with a minimum purity level of 99.999 percent purity. 
     
     
         8 . The method of  claim 1 , wherein adding to said silicon feedstock material the quantity of germanium includes adding germanium in a silicon-germanium alloy of the form Si x Ge (1-x)  with 0<x<1. 
     
     
         9 . The method of  claim 1 , wherein adding to said silicon feedstock material the quantity of germanium includes adding germanium in a concentration ranging from 10 to 40 ppmw. 
     
     
         10 . The method of  claim 1 , further comprising the step of adding to said silicon feedstock material the quantity of germanium ranging from 30 to 40 ppmw. 
     
     
         11 . The method of  claim 1 , further comprising the step of adding to said silicon feedstock material a combination of germanium and gallium. 
     
     
         12 . The method of  claim 11 , wherein adding to said silicon feedstock material a combination of germanium and gallium includes adding gallium in a concentration between 0 and 10 ppmw gallium.