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 within an airtight vessel formed of a 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,  
 sealing said crucible or boat containing said compound raw 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 compound 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 of 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 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 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. The method of preparing a carbon-doped group 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. Vertical boat growth of single crystal, semi- insulating GaAs ingots having controlled planned target levels of Carbon therein comprising:  ( a )  loading a crucible with a charge of poly - crystal GaAs material; a source of carbon; and Boron Oxide over a selectively oriented seed crystal;  ( b )  placing said crucible in a closed quartz tube;  ( c )  applying a controlled pattern of heating to melt the charge and a portion of the seed crystal to sequentially freeze the melt starting at the interface with the seed crystal to form a single crystal; wherein said source of carbon is carbon powder in a selected quantity having a defined large nominal doping potential compared to the planned target level of Carbon in an as grown ingot; and said Boron Oxide is provided in an amount for providing spacer material between an as grown ingot and a crucible wall, and between a seed crystal and the bottom of said crucible.   
     
     
       24. Vertical boat growth of single crystal, semi- insulating GaAs ingots in accordance with    claim 23    wherein said pattern of heating comprises: heating said charge to the melting point temperature of GaAs; holding that temperature for a period of time.   
     
     
       25. Vertical boat growth of single crystal, semi- insulating GaAs ingots in accordance with    claim 23    wherein the nominal doping potential of said carbon powder included in the charge is the order of  100  times the planned target level of carbon dopant in an as grown ingot.   
     
     
       26. Vertical boat growth of single crystal, semi- insulating GaAs ingots in accordance with    claim 23    wherein the nominal doping potential of said carbon powder included in the charge is at least several times the planned target level of carbon dopant in an as grown ingot.   
     
     
       27. The method of any of claims  1 -   22  wherein sufficient boron oxide substance is placed in said crucible or boat so that the boron oxide substance surrounds the melted semiconductor compound.   
     
     
       28. The method of  claim 27  wherein said melting and solidifying is conducted in a vertical furnace. 
     
     
       29. The method of any of claims  1 -   22  wherein said melting and solidifying is conducted in a vertical furnace.   
     
     
       30. The method of any of claims  2 -   10  or  18   -   22  wherein said solid carbon is powdered carbon.   
     
     
       31. The method of  claim 30  wherein sufficient boron oxide substance is placed in said crucible or boat so that the boron oxide substance surrounds the melted semiconductor compound. 
     
     
       32. The method of  claim 30  wherein said melting and solidifying is conducted in a vertical furnace. 
     
     
       33. The method of any of claims  2 -   10  or  18   -   22  wherein said solid carbon is carbon fibers.   
     
     
       34. The method of  claim 33  wherein sufficient boron oxide substance is placed in said crucible or boat so that the boron oxide substance surrounds the melted semiconductor compound. 
     
     
       35. The method of  claim 33  wherein said melting and solidifying is conducted in a vertical furnace. 
     
     
       36. A method of preparing a carbon- doped group III - V compound semiconductor comprising the steps of:      melting a boron oxide substance in contact with carbon, thereby forming a boron oxide - carbon mixture,        heating and melting a III - V compound semiconductor raw material together with said boron oxide - carbon mixture in a boat,        maintaining said compound raw material in melted form in said boat for a period to permit carbon to migrate from said boron oxide - carbon mixture into said compound raw material, and        solidifying said melted compound raw material in said boat to form a crystalline carbon - doped compound semiconductor,        wherein the amount of carbon in the initial boron oxide - carbon mixture is larger than the amount of carbon doped into said compound semiconductor.     
     
     
       37. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 36   , wherein said boron oxide substance comprises boron oxide and water.   
     
     
       38. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 37   , wherein said boron oxide substance contains  10   -   500  wt ppm of said water.   
     
     
       39. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 36   , wherein said amount of said carbon in contact with said melted boron oxide substance is at least  10  times larger than said amount of carbon doped into said crystalline semiconductor.   
     
     
       40. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 36   , further comprising a step of subjecting solid carbon to a heat treatment under reduced pressure before melting said boron oxide substance in contact with said carbon.   
     
     
       41. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 40   , 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.   
     
     
       42. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 41   , further comprising a step of maintaining said melted compound raw material in a melted state for a certain time period before said step of solidifying said melted raw material.   
     
     
       43. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 42   , wherein said step of maintaining said melted compound raw material in a melted state is carried out for  3   -   72  hours.   
     
     
       44. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 36   , further comprising selecting a target amount of said carbon to be doped into said compound semiconductor crystal, and adjusting said amount of said carbon in contact with said melted boron oxide substance so as to responsively achieve said target amount of said carbon to be doped into said semiconductor crystal.   
     
     
       45. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 36   , wherein said carbon comprises powder carbon.   
     
     
       46. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 38   , wherein said carbon comprises powder carbon.   
     
     
       47. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 36   , wherein said carbon comprises fiber carbon.   
     
     
       48. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 38   , wherein said carbon comprises fiber carbon.   
     
     
       49. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 36   , wherein said compound raw material comprises GaAs, and wherein said compound semiconductor crystal comprises a single crystal of GaAs.   
     
     
       50. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , carried out such that said carbon - doped compound semiconductor crystal has a variation of carbon concentration of not more than  8   1 / 3   %  between a lowest carbon concentration and a highest carbon concentration, relative to said lowest carbon concentration.   
     
     
       51. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , wherein said boron oxide substance comprises boron oxide and water.   
     
     
       52. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 51   , wherein said boron oxide substance contains  10   -   500  wt ppm of said water.   
     
     
       53. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , wherein said amount of said carbon in contact with said melted boron oxide substance is at least  10  times larger than said amount of carbon doped into said compound semiconductor crystal.   
     
     
       54. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , further comprising a step of subjecting solid carbon to a heat treatment under reduced pressure before melting said boron oxide substance in contact with said carbon.   
     
     
       55. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 54   , 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.   
     
     
       56. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , further comprising a step of maintaining said melted compound raw material in a melted state for a certain time period before said step of solidifying said melted raw material to grow said crystal.   
     
     
       57. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 51   , wherein said step of maintaining said melted compound raw material in a melted state is carried out for  3   -   72  hours.   
     
     
       58. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , further comprising selecting a target amount of said carbon to be doped into said compound semiconductor crystal, and adjusting said amount of said carbon in contact with said melted boron oxide substance so as to responsively achieve said target amount of said carbon to be doped into said semiconductor crystal.   
     
     
       59. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , wherein said carbon comprises powder carbon.   
     
     
       60. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 52   , wherein said carbon comprises powder carbon.   
     
     
       61. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 49   , wherein said carbon comprises fiber carbon.   
     
     
       62. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 52   , wherein said carbon comprises fiber carbon.   
     
     
       63. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 36   , further comprising a step of maintaining said melted compound raw material in a melted state for a certain time period before said step of solidifying said melted raw material.   
     
     
       64. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 39   , wherein said carbon comprises powder carbon.   
     
     
       65. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 39   , wherein said carbon comprises fiber carbon.   
     
     
       66. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 53   , wherein said carbon comprises powder carbon.   
     
     
       67. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 53   , wherein said carbon comprises fiber carbon.   
     
     
       68. A method of preparing a carbon- doped group III - V compound semiconductor comprising the steps of:      melting a boron oxide substance in contact with carbon, thereby forming a boron oxide - carbon mixture,        heating and melting a III - V compound semiconductor raw material together with said boron oxide - carbon mixture,        maintaining said compound raw material in melted form for a period to permit carbon to migrate from said boron oxide - carbon mixture into said compound raw material, and        solidifying said melted compound raw material to form a crystalline carbon - doped compound semiconductor,        wherein the amount of carbon in the initial boron oxide - carbon mixture is larger than the amount of carbon doped into said compound semiconductor,        further comprising a step of subjecting said carbon to a heat treatment under reduced pressure before melting said boron oxide substance in contact with said carbon.     
     
     
       69. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 68   , 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.   
     
     
       70. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 69   , further comprising a step of maintaining said melted compound raw material in a melted state for a certain time period before said step of solidifying said melted raw material.   
     
     
       71. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 70   , wherein said step of maintaining said melted compound raw material in a melted state is carried out for  3   -   72  hours.   
     
     
       72. A method of preparing a carbon- doped group III - V compound semiconductor comprising the steps of:      melting a boron oxide substance in contact with fiber carbon, thereby forming a boron oxide - carbon mixture,        heating and melting a III - V compound semiconductor raw material together with said boron oxide - carbon mixture,        maintaining said compound raw material in melted form for a period to permit carbon to migrate from said boron oxide - carbon mixture into said compound raw material, and        solidifying said melted compound raw material to form a crystalline carbon - doped compound semiconductor,        wherein the amount of carbon in the initial boron oxide - carbon mixture is larger than the amount of carbon doped into said compound semiconductor.     
     
     
       73. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 72   , wherein said boron oxide substance contains  10   -   500  wt ppm of said water.   
     
     
       74. The method of preparing a carbon- doped group III - V compound semiconductor according to    claim 72   , wherein said amount of said fiber carbon in contact with said melted boron oxide substance is at least  10  times larger than said amount of carbon doped into said crystalline semiconductor.   
     
     
       75. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 72   , wherein said compound raw material comprises GaAs, and wherein said compound semiconductor crystal comprises a single crystal of GaAs.   
     
     
       76. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 75   , wherein said boron oxide substance contains  10   -   500  wt ppm of said water.   
     
     
       77. The method of preparing a carbon- doped group III - V compound semiconductor crystal according to    claim 75   , wherein said amount of said fiber carbon in contact with said melted boron oxide substance is at least  10  times larger than said amount of carbon doped into said compound semiconductor crystal.