High purity gallium for producing compound semiconductor, refining process and apparatus for the same

Abstract

In a process for separating impurities from a raw gallium material containing impurities, a process for refining gallium comprising progressively solidifying a raw gallium material provided in a liquid state inside a vessel while applying stirring, such that the diameter of the tubular solidification boundary gradually advances from the inner wall plane of the vessel towards the center of the vessel to reduce the diameter of the tubular solidification boundary, and separating the liquid phase remaining in the central portion of the vessel from the solidified phase before the entire raw material inside the vessel is solidified. The process above is repeated as required by using, as the raw gallium material, the solidified phase from which the liquid phase is separated. A metallic gallium favorably used for the preparation of a compound semiconductor can be obtained by analyzing the impurity concentration of the impurity-concentrated Ga separated from the solidified layer.

1 . In a process for separating impurities from a raw gallium material containing impurities, a process for refining gallium comprising progressively solidifying a raw gallium material provided in a liquid state inside a vessel while applying stirring, such that the diameter of the tubular solidification boundary gradually advances from the inner wall plane of the vessel towards the center of the vessel to reduce the diameter of the tubular solidification boundary, and separating the liquid phase remaining in the central portion of the vessel from the solidified phase before the entire raw material inside the vessel is solidified.  
     
     
         2 . A process for refining gallium as claimed in  claim 1 , wherein stirring is applied by a magnetic field.  
     
     
         3 . A process for refining gallium as claimed in  claim 1  or  2 , wherein stirring is applied by a magnetic field in such a manner that a circular flow is generated in the liquid phase in the circumferential direction.  
     
     
         4 . In a process for separating impurities from a raw gallium material containing impurities, a process for refining gallium comprising progressively solidifying a raw gallium material provided in a liquid state inside a vessel while applying stirring, such that the diameter of the tubular solidification boundary gradually advances from the inner wall plane of the vessel towards the center of the vessel to reduce the diameter of the tubular solidification boundary, separating the liquid phase remaining in the central portion of the vessel from the solidified phase before the entire raw material inside the vessel is solidified, and after melting the solidified phase inside the vessel, repeating the same process steps above.  
     
     
         5 . A process for refining gallium as claimed in  claim 4 , wherein a solid phase is reserved as a seed crystal on the inner wall plane of the vessel on melting the solidified phase.  
     
     
         6 . An apparatus for refining gallium comprising a vessel having a cylindrical inner wall, a cooling zone attached to the outer peripheral plane of the vessel, a heating zone provided on the inner side of the inner wall of the vessel, a suction pipe installed at the central portion of the vessel, and a magnetic rotator placed on the lower side of the vessel.  
     
     
         7 . An apparatus for refining gallium comprising a vessel having a cylindrical inner wall, a cooling and heating zone attached to the outer peripheral plane of the vessel, a suction pipe installed at the central portion of the vessel, and a magnetic rotator placed on the lower side of the vessel.  
     
     
         8 . An apparatus for refining gallium as claimed in  claim 7 , wherein the cooling and heating zone is operated by switching cold water and hot water to pass therethrough.  
     
     
         9 . An apparatus for refining gallium as claimed in  claim 6 ,  7 , or  8 , wherein a heating zone is provided at the bottom portion of the vessel and to the outer periphery of the suction pipe.  
     
     
         10 . An apparatus for refining gallium as claimed in  claim 6 ,  7 ,  8 , or  9 , wherein a means for reserving a seed crystal is provided to the inner wall of the vessel or in the vicinity of said inner wall.  
     
     
         11 . In a high purity raw Ga material for use in the preparation of a compound semiconductor, a raw Ga material used for preparing a compound semiconductor which has a difference ΔC=|ΣAn−ΣBn| of 5 ppm by atomic or lower when subjected to a “test method for impurity-concentrated Ga” as defined below, where ΣAn represents the total quantity of the components contained in the sample of an impurity-concentrated Ga, which is at least one element of group A components selected from the group consisting of B, Na, Mg, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Au, Hg, Pb, and Bi; and ΣBn represents the total quantity of the components contained in the sample of impurity-concentrated Ga, which is at least one element of group B components selected from the group consisting of F, Si, S, Cl, Ge, Se, Sn, and Te. 
 “Test method for impurity-concentrated Ga” is defined as a test method comprising:  
 using an apparatus for refining gallium comprising a vessel, having a cylindrical inner wall made of a 3 mm thick SUS304 steel sheet provided with a 0.3 mm thick fluororesin coated inner wall plane, said vessel having an inner radius of 60 mm and a height of 40 mm, a cooling zone attached to the outer peripheral plane of said vessel, a suction pipe installed at the central portion of said vessel, and a magnetic rotator provided to the lower portion of said vessel;  
 filling said vessel with a raw Ga material in liquid state at a quantity as such that it amounts to 30 mm in height inside the vessel while purging the space inside the vessel with an inert gas; and  
 obtaining a sample of impurity-concentrated Ga as follows: 
 while applying a circular flow of 100±10 rpm to the liquid raw Ga material by using the rotator, maintaining the liquid raw Ga material at a temperature of 29.6±0.5° C., and passing a cooling water at a temperature of 5° C. through the cooling zone, thereby allowing progressive solidification of the liquid to proceed from the inner wall of the vessel towards the central portion of the vessel at a solidification rate as such that the entire liquid may solidify in 60±5 minutes, then sampling the liquid phase through the suction pipe when the radius of the remaining liquid phase becomes 20 mm.  
 
 
     
     
         12 . A raw Ga material used for preparing a compound semiconductor as claimed in  claim 11 , wherein said compound semiconductor is a single crystal of GaAs.  
     
     
         13 . A raw Ga material used for preparing a compound semiconductor as claimed in  claim 11 , wherein said compound semiconductor is a crystal of GaP.  
     
     
         14 . A raw Ga material used for preparing a compound semiconductor as claimed in  claim 11 ,  12 , or  13 , wherein ΣAn is 1 ppm by atomic or lower.  
     
     
         15 . A raw Ga material used for preparing a compound semiconductor as claimed in  claim 11 ,  12 , or  13 , wherein ΣBn is 1 ppm by atomic or lower.  
     
     
         16 . A raw Ga material used f or preparing a compound semiconductor, having a refined purity of 6N as refined by the process of refining gallium as claimed in  claim 1 .  
     
     
         17 . A raw Ga material used for preparing a compound semiconductor, having a refined purity of 7N or higher as refined by the process of refining gallium as claimed in  claim 1.