Crystal preparing device, crystal preparing method, and crystal

Abstract

In a crystal preparing device, a crucible holds a mixed molten metal containing alkali metal and group III metal. A container has a container space contacting the mixed molten metal and holds a molten alkali metal between the container space and an outside of the container, the molten alkali metal contacting the container space. A gas supply device supplies nitrogen gas to the container space. A heating device heats the crucible to a crystal growth temperature. The crystal preparing device is provided so that a vapor pressure of the alkali metal which evaporates from the molten alkali metal is substantially equal to a vapor pressure of the alkali metal which evaporates from the mixed molten metal.

1 . A crystal preparing device comprising:
 a crucible holding a mixed molten metal containing alkali metal and group III metal;   a reaction container having a container space which contacts the mixed molten metal and holding a molten alkali metal between the container space and an outside of the container, the molten alkali metal contacting the container space;   a gas supply device supplying a nitrogen gas to the container space; and   a heating device heating the crucible to a crystal growth temperature,   wherein the crystal preparing device is provided so that a vapor pressure of the alkali metal which evaporates from the molten alkali metal is substantially equal to a vapor pressure of the alkali metal which evaporates from the mixed molten metal.   
   
   
       2 . The crystal preparing device according to  claim 1 , further comprising a heater/condenser controlling a temperature of the molten alkali metal to a specific temperature at which a vapor pressure of the alkali metal which evaporates from the molten alkali metal is substantially balanced with a vapor pressure of the alkali metal which evaporates from the mixed molten metal. 
   
   
       3 . The crystal preparing device according to  claim 1 , wherein a temperature of the molten alkali metal is lower than a temperature of the mixed molten metal. 
   
   
       4 . The crystal preparing device according to  claim 1 , further comprising a piping disposed below the crucible and connected with the reaction container, wherein the crucible is contained in the reaction container and the molten alkali metal is held at least in the piping. 
   
   
       5 . The crystal preparing device according to  claim 4 , wherein the molten alkali metal is held only in the piping. 
   
   
       6 . The crystal preparing device according to  claim 1 , wherein the gas supply device supplies nitrogen gas to the container space of the reaction container through the alkali molten metal. 
   
   
       7 . A crystal preparing method which produces a group III nitride crystal using a crystal preparing device, the crystal preparing device including a crucible holding a mixed molten metal containing alkali metal and group III metal, a reaction container having a container space which contacts the mixed molten metal and holding a molten alkali metal between the container space and an outside of the container, the molten alkali metal contacting the container space, and a piping disposed below the crucible and connected with the reaction container, the crystal preparing method comprising:
 a first step of placing the alkali metal and the group III metal into the crucible in an inert gas or nitrogen gas atmosphere;   a second step of placing the alkali metal into the piping in the inert gas or nitrogen gas atmosphere;   a third step of filling the container space of the reaction container with nitrogen gas;   a fourth step of heating the crucible to a crystal growth temperature;   a fifth step of heating the molten alkali metal at a specific temperature at which a vapor pressure of the alkali metal which evaporates from the molten alkali metal is substantially equal to a second vapor pressure of the alkali metal which evaporates from the mixed molten metal; and   a sixth step of holding a temperature of the crucible to the crystal growth temperature, and holding a temperature of the molten alkali metal to the specific temperature for a predetermined time.   
   
   
       8 . The crystal preparing method according to  claim 7 , wherein the specific temperature is lower than the crystal growth temperature. 
   
   
       9 . The crystal preparing method according to  claim 7 , wherein the crystal preparing device further includes a molten metal holding member provided in the piping to hold the molten alkali metal by a surface tension of the alkali molten metal, and wherein the second step is provided to place the alkali metal between the crucible and the reaction container so that the molten alkali metal containing the alkali metal is held at least in the piping. 
   
   
       10 . The crystal preparing method according to  claim 9 , wherein the second step is provided to place the alkali metal between the crucible and the reaction container so that the molten alkali metal containing the alkali metal is held only in the piping. 
   
   
       11 . The crystal preparing method according to  claim 7  further comprising a seventh step of supplying nitrogen gas to the container space through the molten alkali metal after the fifth step is performed. 
   
   
       12 . A crystal preparing method which produces a group III nitride crystal using a crystal preparing device including a reaction container holding a mixed molten metal containing alkali metal and group III metal, the crystal preparing method comprising:
 a first step of placing the alkali metal and the group III metal in a reaction container in an inert gas or nitrogen gas atmosphere containing a predetermined amount of impurities;   a second step of filling a container space of the reaction container with nitrogen gas;   a third step of heating the reaction container to a crystal growth temperature;   a fourth step of holding a temperature of the reaction container at the crystal growth temperature for a predetermined time; and   a fifth step of supplying nitrogen gas to the reaction container to hold a pressure in the container space of the reaction container at a predetermined pressure.   
   
   
       13 . The crystal preparing method according to  claim 12 , wherein the predetermined amount of impurities contains oxygen gas of 10 ppm or less. 
   
   
       14 . The crystal preparing method according to  claim 13 , wherein the predetermined amount of impurities contains oxygen gas of 0.1-10 ppm. 
   
   
       15 . The crystal preparing method according to  claim 13 , wherein the predetermined amount of impurities contains oxygen gas below 0.1 ppm. 
   
   
       16 . The crystal preparing method according to  claim 12 , wherein the predetermined amount of impurities contains oxygen gas of 10 ppm or less and moisture of 10 ppm or less. 
   
   
       17 . The crystal preparing method according to  claim 16 , wherein the predetermined amount of impurities contains oxygen gas of 0.1-10 ppm and moisture of 0.1-10 ppm. 
   
   
       18 . The crystal preparing method according to  claim 16 , wherein the predetermined amount of impurities contains oxygen gas below 0.1 ppm and moisture of 0.1-10 ppm. 
   
   
       19 . The crystal preparing method according to  claim 16 , wherein the predetermined amount of impurities contains oxygen gas of 0.1-10 ppm and moisture below 0.1 ppm. 
   
   
       20 . The crystal preparing methods according to  claim 12 , wherein the predetermined amount of impurities contains moisture of 10 ppm or less. 
   
   
       21 . The crystal preparing method according to  claim 20 , wherein the predetermined amount of impurities contains moisture of 0.1-10 ppm. 
   
   
       22 . The crystal preparing method according to  claim 20 , wherein the predetermined amount of impurities contains moisture below 0.1 ppm. 
   
   
       23 . The crystal preparing method according to  claim 12 , further comprising a sixth step of heating the reaction container holding an intermetallic compound of the alkali metal and the group III metal under a predetermined reduced pressure, wherein the intermetallic compound is placed, in the first step, in the reaction container in the inert gas or nitrogen gas atmosphere, and the second to fifth steps are performed after the sixth step is performed. 
   
   
       24 . A group III nitride crystal containing group III metal and nitrogen, wherein the group III nitride crystal has a dislocation density of 10 3 cm −2  or less and contains oxygen in a concentration of 10 20 cm −3  or less. 
   
   
       25 . The group III nitride crystal according to  claim 24 , wherein the concentration of oxygen is in a range of 10 18 - 10   20 cm −3 . 
   
   
       26 . The group III nitride crystal according to  claim 24 , wherein the concentration of oxygen is lower than 10 18 cm −3 . 
   
   
       27 . The group III nitride crystal according to  claim 24 , wherein the group III nitride crystal further contains hydrogen in a concentration of 10 20 cm −3  or less. 
   
   
       28 . The group III nitride crystal according to  claim 27 , wherein the concentration of hydrogen is in a range of 10 19 -10 20 cm −3 . 
   
   
       29 . The group III nitride crystal according to  claim 27 , wherein the concentration of hydrogen is lower than 10 19 cm −3 . 
   
   
       30 . The group III nitride crystal according to  claim 24 , wherein the group III nitride crystal further contains alkali metal.