Method of preparing group III-V compound semiconductor crystal

Abstract

A method is provided for preparing, with high reproducibility, a carbon-doped group III-V compound semiconductor crystal having favorable electrical characteristics and having impurities removed therefrom, and in which the amount of doped carbon can be adjusted easily during crystal growth. This method includes the steps of: filling a crucible with compound raw material, solid carbon, and boron oxide; sealing the filled crucible gas impermeable material; heating and melting the compound raw material under the sealed state in the airtight vessel; and solidifying the melted compound raw material to grow a carbon-doped compound semiconductor crystal.

1. A method of preparing a carbon-doped group III-V compound semiconductor crystal, comprising the steps of:
 placing a compound raw material, solid carbon, and a boron oxide substance into a crucible or a boat,    scaling said crucible or boat containing said compound Law material, said solid carbon, and said boron oxide substance within an airtight vessel formed of a gas impermeable material,    heating and melting said compound raw material in said crucible or said boat sealed within said airtight vessel, and    solidifying said melted compound raw material to grow a carbon-doped component semiconductor crystal,    wherein an amount of said solid carbon placed into said crucible or said boat is larger than an amount of carbon doped into said compound semiconductor crystal.    
     
     
       2. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , further comprising a step of heating and melting said boron oxide substance and having said melted boron oxide substance in contact with at least a portion of said solid carbon, during said step of heating and melting said compound raw material. 
     
     
       3. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said gas impermeable material comprises a material selected from the group consisting of quartz and pBN. 
     
     
       4. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said boron oxide substance comprises boron oxide and water. 
     
     
       5. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 4 , wherein said boron oxide substance contains 10-500 wt ppm of said water. 
     
     
       6. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said amount of said solid carbon placed into said crucible or said boat is at least 10 times larger than said amount of carbon doped into said compound semiconductor crystal. 
     
     
       7. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , further comprising a step of subjecting said solid carbon to a heat treatment under reduced pressure before placing said solid carbon into said crucible or said boat. 
     
     
       8. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 7 , comprising carrying out said heat treatment for 1 hour to 12 hours at a temperature of 500° C.-2000° C. under a pressure of 1 Torr −1×10 −8  Torr. 
     
     
       9. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , further comprising a step of maintaining said melted compound raw material in a melted state for a certain time period before said step solidifying said melted raw material to grow said crystal. 
     
     
       10. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 9 , wherein said step of maintaining said melted compound raw material in a melted state is carried out for 3-72 hours. 
     
     
       11. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said solid carbon comprises powder carbon. 
     
     
       12. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 11 , wherein said powder solid carbon has a grain size of not more than 100 μm. 
     
     
       13. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said solid carbon comprises fiber carbon. 
     
     
       14. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 13 , wherein said fiber solid carbon has an average diameter of not more than 50 μm. 
     
     
       15. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said solid carbon comprises bulk carbon. 
     
     
       16. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 15 , wherein said bulk carbon has a disk shape with a disk diameter smaller than an inner diameter of said crucible. 
     
     
       17. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 15 , wherein said bulk carbon comprises a sintered compact of carbon powder. 
     
     
       18. A method of preparing a carbon-doped III-V compound semiconductor crystal according to  claim 1 , wherein said crucible or said boat comprises pBN. 
     
     
       19. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , wherein said compound raw material comprises GaAs, and wherein said compound semiconductor crystal comprises a GaAs crystal. 
     
     
       20. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 2 , further comprising having said melted boron oxide substance in contact with at least a portion of said melted compound raw material, during said step of heating and melting said compound raw material. 
     
     
       21. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , further comprising selecting a target amount of said carbon to be doped into said compound semiconductor crystal, and adjusting said amount of said solid carbon placed into said crucible or said boat so as to responsively achieve said target amount of said carbon to be doped into said semiconductor crystal. 
     
     
       22. The method of preparing a carbon-doped group III-V compound semiconductor crystal according to  claim 1 , carried out such that said carbon-doped compound semiconductor crystal has a variation of carbon concentration of not more than 8⅓% between a lowest carbon concentration and a highest carbon concentration, relative to said lowest carbon concentration. 
     
     
       23. A method for making a cylindrical section of a carbon doped, GaAs semiconductor crystal, said crystal section comprising:
   a concentration of doped carbon not less than  0 . 8 × 10     15    cm   −3   ,        a dislocation density of not more than  4000  cm   −2   , and        a diameter of not less than about  100  mm;      
       
         said method comprising the steps of:  
           filling a vertical crucible or boat with pre - synthesized GaAs raw material and boron oxide,    
         
           melting the GaAs raw material and boron oxide in the presence of a carbon source, and  
         
         
           growing a single crystal by control of the temperature of the melted material to solidify the melted material in the vertical crucible or boat.  
         
       
     
     
       24. The method for making a GaAs semiconductor crystal section according to  claim 23 , wherein said melting step a molten boron oxide layer covers the upper surface of the melted raw material.  
     
     
       25. The method for making a GaAs semiconductor crystal section according to  claim 24 , wherein the thickness of said molten boron oxide layer is not less than  5  mm.  
     
     
       26. The method for making a GaAs semiconductor crystal section according to any of claims  23 - 25 , wherein said crystal is grown within an airtight vessel formed of a gas impermeable material.  
     
     
       27. The method for making a GaAs semiconductor crystal section according to  claim 26 , wherein the carbon source is put in an airtight vessel formed of a gas impermeable material.  
     
     
       28. The method for making a GaAs semiconductor crystal section according to  claim 27 , wherein said carbon source is solid carbon.  
     
     
       29. The method for making a GaAs semiconductor crystal section according to  claim 28 , wherein said carbon source is put in said crucible or boat with said raw material and boron oxide.  
     
     
       30. The method for making a GaAs semiconductor crystal section according to  claim 23 , wherein the concentration of doped carbon in said crystal section is not less than  2 . 3 × 10   15    cm   −3   .    
     
     
       31. The method for making a GaAs semiconductor crystal section according to  claim 23 , wherein the concentration of doped carbon in said crystal section is not less than  6 . 5 × 10   15    cm   −3   .    
     
     
       32. The method for making a GaAs semiconductor crystal section according to  claim 23 , wherein said crystal section has dislocation density of not more than  2000  cm −2   .    
     
     
       33. The method for making a GaAs semiconductor crystal section according to  claim 23 , wherein the length of said crystal section is not less than  100  mm.  
     
     
       34. The method for making a GaAs semiconductor crystal section according to  claim 33 , wherein said crystal section has a variation of carbon concentration of not more than  8   1 / 3 %  between a lowest carbon concentration and highest carbon concentration, relative to said lowest carbon concentration.    
     
     
       35. A carbon doped GaAs semiconductor crystal with a diameter not less than about  100  mm, wherein the concentration of doped carbon is not less than  0 . 8 × 10   15    cm   −3    and the dislocation density is not more than  4000  cm   −2   .    
     
     
       36. The GaAs semiconductor crystal according to  claim 35 , wherein the concentration of doped carbon is not less than  2 . 3 × 10   15    cm   −3   .    
     
     
       37. The GaAs semiconductor crystal according to  claim 35 , wherein the concentration of doped carbon is not less than  6 . 5 × 10   15    cm   −3   .    
     
     
       38. The GaAs semiconductor crystal according to  claim 35 , wherein said crystal has dislocation density of not more than  2000  cm −2   .    
     
     
       39. The GaAs semiconductor crystal according to  claim 35 , wherein the length of said crystal is not less than  100  mm.  
     
     
       40. The GaAs semiconductor crystal according to  claim 39 , wherein said crystal has a variation of carbon concentration of not more than  8   1 / 3 %  between a lowest carbon concentration and highest carbon concentration, relative to said lowest carbon concentration.    
     
     
       41. The GaAs semiconductor crystal according to  claim 35 , wherein the length of said crystal is not less than  200  mm.