JP2011207676A - Method for producing group iii nitride semiconductor crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a GaN crystal by an Na flux method that increases a crystal growth rate and a growth amount as well as improves uniformity in the thickness of a crystal.SOLUTION: While a GaN crystal is grown by an Na flux method, the distance from the GaN crystal surface in a mixture melt to a gas-liquid interface is kept to 10 mm or less, and a crucible and a seed crystal are independently rotated in the following rotation mode. That is, the rotation direction of the crucible is periodically inverted, so that the rotation direction of the seed crystal is completely opposite to the rotation direction of the crucible. By growing the GaN crystal while rotating the crucible and the seed crystal under the above conditions, the growth rate of the GaN crystal can be raised to increase the growth amount and the GaN crystal can be formed into a uniform thickness.

Description

  The present invention relates to a method for producing a group III nitride semiconductor crystal on a seed crystal by a flux method, which shortens the growth time of the crystal, increases the growth amount, and improves the in-plane uniformity of the crystal. The present invention relates to a method for producing a group III nitride semiconductor crystal.

  A so-called Na flux method is known as a method for producing a group III nitride semiconductor crystal such as GaN. In this Na flux method, a mixed melt of Na (sodium) and Ga (gallium) and a seed crystal are held in a crucible, and dissolved and diffused by dissolving nitrogen in the mixed melt at about 800 ° C. and several tens of atmospheres. In this method, nitrogen in the melt is brought into a supersaturated state, and Ga and nitrogen are reacted to grow GaN on the seed crystal.

  In manufacturing a GaN crystal by the Na flux method, there are methods described in Patent Documents 1 and 2 as a method for making the thickness of the GaN crystal uniform.

  In Patent Document 1, by setting the distance from the gas-liquid interface to the seed crystal surface to be 5 mm or more, nitrogen is sufficiently diffused into the melt so that a GaN crystal having a uniform thickness can be grown in the plane. Yes.

  In Patent Document 2, as the crystal growth progresses, the distance between the gas-liquid interface and the seed crystal is increased to slow the growth rate, so that nitrogen is sufficiently diffused into the melt, and the uniform thickness is increased. A GaN crystal is obtained.

JP2007-254161 JP2009-203132A

  In the Na flux method, nitrogen dissolves from the gas-liquid interface into the mixed melt, but if the distance from the gas-liquid interface to the seed crystal surface in the mixed melt is long, nitrogen diffuses to the seed crystal surface. It takes a long time to start the growth of the GaN crystal, and it takes time to grow the crystal. Therefore, even if the amount of the mixed melt is increased in order to increase the growth amount of GaN, the liquid level (the height from the bottom of the crucible to the gas-liquid interface) increases and the time for diffusion of nitrogen into the mixed melt increases. Therefore, the start of GaN growth is delayed, and it takes time to form a thick GaN crystal.

  It is conceivable to increase the crystal growth rate by bringing the seed crystal closer to the gas-liquid interface, but if the distance from the gas-liquid interface to the seed crystal is too short, nitrogen will not be uniformly diffused into the mixed melt and mixing will occur. Since the concentration of nitrogen in the melt varies, irregularities occur on the surface of the GaN crystal, and the thickness is not uniform.

  In the methods of Patent Literatures 1 and 2, there is a trade-off relationship between obtaining a uniform GaN crystal and increasing the growth rate of the GaN crystal, and the problem is that both cannot be satisfied simultaneously. Further, the method of Patent Document 2 is described as a method for producing a thin GaN crystal having a thickness of about several tens of μm by reducing the amount of the mixed melt to improve the crystal speed. This technique cannot be applied to a method of manufacturing a thick GaN crystal of about 100 μm to several mm.

  Therefore, an object of the present invention is to increase the growth rate by increasing the rate of crystal growth and to make the crystal thickness uniform in a method for producing a group III nitride semiconductor crystal by a flux method. is there.

  According to a first aspect of the present invention, a mixed melt containing at least a group III metal and an alkali metal and a seed crystal are held in a crucible, and the mixed melt and a gas containing at least nitrogen are reacted to form III on the seed crystal. In the method for producing a group III nitride semiconductor crystal for growing a group nitride semiconductor crystal, the mixed melt is obtained from the surface of the group III nitride semiconductor crystal in the mixed melt during the step of growing the group III nitride semiconductor crystal. The distance to the gas-liquid interface between the gas and the gas is maintained at 10 mm or less, the seed crystal and the crucible are rotated independently, and the rotation direction of the seed crystal is opposite to the rotation direction of the crucible. This is a method for producing a group III nitride semiconductor crystal.

Here, the group III nitride semiconductor is a semiconductor represented by the general formula Al _x Ga _y In _z N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), and a part of Al, Ga, and In Is replaced with other group 13 elements (group 3B elements) B or Tl, and part of N is replaced with other group 15 elements (group 5B elements) P, As, Sb, Bi. Including replacements. More generally, GaN, InGaN, AlGaN, or AlGaInN containing at least Ga is shown.

  The group III metal is at least one of Ga, Al, and In. In particular, it is desirable to manufacture a GaN crystal using only Ga.

  As the alkali metal, Na (sodium) is usually used, but K (potassium) may be used, or a mixture of Na and K may be used. Furthermore, Li (lithium) or an alkaline earth metal may be mixed. In addition, dopants are added to the mixed melt for purposes such as controlling the physical properties of III-nitride semiconductors for crystal growth, properties such as magnetism, promoting crystal growth, suppressing miscellaneous crystals, and controlling the growth direction. May be. For example, when C (carbon) is added, effects of suppressing miscellaneous crystals and promoting crystal growth can be obtained. Further, Ge (germanium) or the like can be used as the n-type dopant, and Zn (zinc) or the like can be used as the p-type dopant.

  The gas containing nitrogen is a gas of a compound containing nitrogen as a constituent element, such as nitrogen molecules or ammonia, and may be a mixed gas thereof, or may further contain an inert gas such as a rare gas. .

  The distance from the surface of the group III nitride semiconductor crystal to the gas-liquid interface may be 10 mm or less, and the distance may vary within a range of 10 mm or less. However, it is desirable to maintain a certain distance as much as possible within a range of 10 mm or less. The distance to the gas-liquid interface is preferably 1 mm or more. This is because the nitrogen concentration of the mixed melt on the surface of the group III nitride semiconductor crystal is more uniform. More desirable is 2 to 10 mm. The distance to the gas-liquid interface may be controlled by moving either the seed crystal or the crucible, or may be controlled by moving both.

  The rotation speed of the seed crystal and the crucible is desirably 1 to 30 rpm. If it is slower than 1 rpm, the mixed melt can hardly be agitated, resulting in variations in the thickness and crystallinity of the Group III nitride semiconductor crystal, which is undesirable. If it is faster than 30 rpm, the Group III metal in the mixed melt is not desirable. This is not desirable because there is a bias in the concentration of the material, and miscellaneous crystals are generated and adhered to the side wall of the crucible. A more desirable rotation speed is 1 to 25 rpm. The rotation speed of the seed crystal and the rotation speed of the crucible may be different or the same.

  It is desirable to periodically reverse the rotation direction of the crucible and the seed crystal. Only in one direction of rotation, the mixed melt near the rotation axis stops, so the crystal growth near the rotation axis becomes slow or ungrown, and the group III nitride semiconductor crystal with a recessed central part Will grow. The inversion period is desirably 8 seconds to 8 minutes. Within this range, the mixed melt can be efficiently stirred to obtain a uniform concentration distribution, and the crystallinity and thickness of the group III nitride semiconductor crystal can be made more uniform. More preferably, the inversion is performed at a period of 15 seconds to 7 minutes. Moreover, when reversing the rotation direction, a time during which one or both of the crucible and the seed crystal are not rotated may be provided. If the direction of rotation is suddenly reversed, turbulent flow may occur in the mixed melt, and the crystallinity and thickness uniformity of the group III nitride semiconductor crystal will deteriorate. Similarly, in order to prevent deterioration in crystallinity and thickness uniformity, it is preferable to gradually decrease the rotational speed when reversing and then gradually increase the rotational speed in the reverse direction. Further, the rotation speed in one rotation direction may be different from the rotation speed in the reversed rotation direction.

  The rotation axis of the crucible and the rotation axis of the seed crystal are not necessarily the same axis, and need not be in the same direction. Furthermore, the rotation axis of the crucible and the rotation axis of the seed crystal may form an angle. Moreover, it is not a simple rotation but may be a motion such as a precession motion in which the rotation axis fluctuates.

  The molar ratio of the group III metal to the entire mixed melt at the start of crystal growth is preferably 15 to 30%. Outside this range, the growth rate of the group III nitride semiconductor crystal is slow, and the growth amount of the group III nitride semiconductor crystal is reduced to deteriorate productivity. More desirable is 18 to 30%. The entire mixed melt is the total of alkali metal and group III metal, and may be the total of all of alkali metal, group III metal, other dopants, and the like.

  The pressure for crystal growth is desirably 2.5 to 4.0 MPa. When the pressure is lower than 2.5 MPa, the group III nitride semiconductor crystal does not grow, and when the pressure is higher than 4.0 MPa, many miscellaneous crystals are generated. A more desirable pressure is 2.7-4 MPa.

  A second invention is a method for producing a group III nitride semiconductor crystal according to the first invention, wherein the rotation speed of the seed crystal and the crucible is 1 to 30 rpm.

  A third invention is a method for producing a group III nitride semiconductor crystal according to the first invention or the second invention, wherein the rotation directions of the seed crystal and the crucible are alternately reversed at a constant period. .

  A fourth invention is the method for producing a group III nitride semiconductor crystal according to the third invention, wherein the period for switching the rotation direction is 8 seconds to 8 minutes.

  The fifth invention is the group III nitride according to the first to fourth inventions, wherein the molar ratio of the group III metal to the entire mixed melt at the start of crystal growth is 15 to 30%. It is a manufacturing method of a semiconductor crystal.

  A sixth invention is a method for producing a Group III nitride semiconductor crystal according to any one of the first to fifth inventions, wherein the pressure for crystal growth is 2.5 to 4.0 MPa.

  A seventh invention is a method for producing a group III nitride semiconductor crystal according to the first to sixth inventions, wherein the group III nitride semiconductor crystal is grown to a thickness of 1 mm or more. is there.

  According to an eighth invention, in the first to seventh inventions, the distance from the bottom of the crucible to the gas-liquid interface at the start of crystal growth is 20 mm or more. It is a manufacturing method.

  However, the distance from the bottom of the crucible to the gas-liquid interface is preferably 150 mm or less. This is because if the distance is longer than this, the amount of the mixed melt is large and it becomes difficult to stir efficiently.

  According to the first invention, since the distance from the group III nitride semiconductor crystal surface to the gas-liquid interface in the mixed melt is 10 mm or less, the nitrogen in the mixed melt is supersaturated on the group III nitride semiconductor crystal surface. Thus, the time required for the growth of the group III nitride semiconductor crystal can be accelerated, and the growth amount of the crystal can be improved. In addition, since the crucible and the seed crystal are rotated independently so that the rotation direction of the crucible and the rotation direction of the seed crystal are reversed, the mixed melt can be efficiently stirred, and the group III nitride The concentration of the mixed melt on the semiconductor crystal surface can be made uniform. Therefore, the thickness and crystallinity of the group III nitride semiconductor crystal can be made uniform. In particular, the present invention can grow a thick group III nitride semiconductor crystal in a short time even when the amount of mixed melt is increased in order to increase the amount of group III nitride semiconductor crystal grown. In addition, the thickness can be made uniform.

  Further, according to the second to fourth inventions, the mixed melt can be more efficiently stirred, and the elements constituting the mixed melt are more uniformly dispersed and the concentration distribution becomes uniform. The thickness and crystallinity of the nitride semiconductor crystal can be made more uniform.

  Further, according to the fifth invention, the growth rate of the group III nitride semiconductor crystal can be increased and the growth amount can be further improved.

  Moreover, according to the sixth invention, the crystallinity of the group III nitride semiconductor crystal can be further improved.

  Further, as in the seventh invention, the present invention is particularly effective when a group III nitride semiconductor crystal is grown to 1 mm or more by the flux method, and the crystal growth time can be shortened as compared with the conventional manufacturing method. And the thickness can be made uniform.

  In addition, as in the eighth aspect of the present invention, the liquid level (height from the bottom of the crucible to the gas-liquid interface) is set to 20 mm or more, the amount of the mixed melt is increased, and the growth amount of the group III nitride semiconductor crystal is increased. It is effective when you want to do more.

The figure which showed the structure of the manufacturing apparatus 1 used for the manufacturing method of the GaN crystal of Example 1. FIG. The graph which showed the rotation mode of the crucible 12 and the seed crystal 18. FIG.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram showing a configuration of a manufacturing apparatus 1 used in the GaN crystal manufacturing method of Example 1. The production apparatus 1 includes a pressure vessel 10, a reaction vessel 11, a crucible 12, a heating device 13, supply pipes 14 and 16, exhaust pipes 15 and 17, a rotation device 19 that rotates the crucible, and a seed crystal. The holding tool 20 to hold | maintain is comprised.

  The pressure vessel 10 is made of cylindrical stainless steel and has pressure resistance. A supply pipe 16 and an exhaust pipe 17 are connected to the pressure vessel 10. A reaction vessel 11 and a heating device 13 are disposed inside the pressure vessel 10. The reaction vessel 11 has heat resistance. A crucible 12 is disposed in the reaction vessel 11. The crucible 12 is, for example, W (tungsten), Mo (molybdenum), BN (boron nitride), alumina, YAG (yttrium aluminum garnet), or the like. The crucible 12 holds a mixed melt 21 containing Ga and Na, and a seed crystal 18 is held in the mixed melt 21. A supply pipe 14 and an exhaust pipe 15 are connected to the reaction container 11, and ventilation in the reaction container 11, supply of nitrogen, and reaction container 11 are performed by valves (not shown) provided in the supply pipe 14 and the exhaust pipe 15. Control the pressure inside. Further, nitrogen is also supplied from the supply pipe 16 to the pressure vessel 10, and the pressure in the pressure vessel 10 is adjusted by adjusting the supply amount of nitrogen and the exhaust amount by valves (not shown) of the supply pipe 16 and the exhaust pipe 17. The pressure in the reaction vessel 11 is controlled to be substantially the same. Further, the temperature in the reaction vessel 11 is controlled by the heating device 13.

  The rotating device 19 includes a pedestal 191 that holds the crucible 12, a rotating shaft 192 that is connected to the pedestal 191 and extends vertically downward, and a driving device 193. The drive device 193 moves the rotary shaft 192 up and down in the axial direction (vertical direction) to control the position of the pedestal 191 and the crucible 12 in the vertical direction, and rotates the rotary shaft 192 around the axis to rotate the pedestal 191 and The crucible 12 held on the base 191 is rotated. The rotation direction and rotation speed of the crucible 12 can be controlled to an arbitrary rotation direction and speed by the rotation of the rotation shaft 192 by the driving device 193, and the rotation direction can be reversed.

  The holder 20 includes a pedestal 201 that holds the seed crystal 18, a rotating shaft 202 that is connected to the pedestal 201 and extends vertically upward, and a driving device 203. The drive device 203 moves the rotary shaft 202 up and down in the axial direction (vertical direction) to control the position of the base 201 and the seed crystal 18 in the vertical direction. When the GaN crystal is grown, the seed crystal 18 is mixed with the mixed melt 21. The position of the seed crystal 18 is controlled so that the distance from the surface of the GaN crystal growing on the seed crystal 18 to the gas-liquid interface (interface between the mixed melt 21 and nitrogen) is 10 mm or less. Control the position. Further, the driving device 203 can rotate the rotating shaft 202 around the axis to rotate the pedestal 201 and rotate the seed crystal 18 held on the pedestal 201. The rotation direction and rotation speed of the seed crystal 18 can be controlled to any rotation direction and speed by rotation of the rotation shaft 202 by the driving device 203, and the rotation direction can be reversed.

In addition, a lid 22 that covers the crucible 12 is provided in order to prevent evaporation of Na during GaN crystal growth. The lid 22 has a cylindrical shape, and the upper part is opened so that the rotating shaft 202 of the holder 20 passes therethrough.

  In addition, if the thing with pressure resistance is used as the reaction vessel 11, the pressure vessel 10 is not necessarily required.

  Next, the manufacturing method of the GaN crystal of Example 1 using the manufacturing apparatus 1 will be described.

  First, a GaN template substrate having a diameter of 2 inches was prepared as the seed crystal 18. The GaN template substrate is a substrate in which a GaN layer is formed on a sapphire substrate by HVPE method, MOCVD method or the like.

  Next, Na, Ga, and C were placed in the crucible 12, the crucible 12 was placed in the reaction vessel 11 and placed on the pedestal 191, and the crucible 12 was covered with the lid 22. Further, the reaction vessel 11 was placed in the pressure vessel 10, the seed crystal 18 was placed on the base 201 of the holder 20, and the pressure vessel 10 was sealed. Na or Ga may be placed in the crucible 12 in a solid state, or liquid Na and Ga may be placed in the crucible 12, or liquid Na and Ga may be mixed and then placed in the crucible 12. Also good. The molar ratio of Ga to the total of Na, Ga and C was 18%. C was added to suppress generation of miscellaneous crystals and promote crystal growth.

  Next, the crucible 12 was heated to 860 ° C. by the heating device 13, and the crucible 12 was rotated by the rotating device 19 to generate a mixed melt 21 having a uniform concentration in the crucible 12. Liquid level (height from the bottom of the crucible 12 to the gas-liquid interface) Further, nitrogen is supplied into the reaction vessel 11 through the supply pipe 14 and the exhaust pipe 15 to set the pressure in the reaction vessel 11 to 3 MPa, and the pressure vessel 10 was also supplied with nitrogen from the supply pipe 16 and the exhaust pipe 17 so that the pressure in the pressure vessel 10 was approximately the same as the pressure in the reaction vessel 11.

  Next, the holder 20 is moved vertically downward to hold the seed crystal 18 in the mixed melt 21, and a GaN crystal is grown on the seed crystal 18 while maintaining a temperature of 860 ° C. and a pressure of 3 MPa for 200 hours. did.

  Due to the crystal growth of the GaN crystal, Ga in the mixed melt 21 is consumed, and the position of the gas-liquid interface moves vertically downward over time. Following the change in the position of the gas-liquid interface, the seed crystal 18 is also moved vertically downward, and the distance from the GaN crystal surface growing on the seed crystal 18 to the gas-liquid interface during the growth of the GaN crystal is always 10 mm or less. Controlled to become.

  When the position of the seed crystal 18 is controlled in this way, the distance from the GaN crystal surface to the gas-liquid interface is short, so the time until the nitrogen in the mixed melt 21 on the GaN crystal surface reaches supersaturation is shortened. As a result, the growth start of the GaN crystal is accelerated and the growth amount of the GaN crystal can be improved.

  In addition, it is desirable to maintain a certain distance as much as possible within a range where the distance from the GaN crystal surface to the gas-liquid interface is 10 mm or less. The crystallinity of the GaN crystal can be made more uniform. The distance from the GaN crystal surface to the gas-liquid interface is preferably 1 mm or more. If the distance is shorter than this, the distance in which nitrogen diffuses is too short, so that the nitrogen concentration in the mixed melt 21 is biased on the surface of the GaN crystal, and the thickness and crystallinity uniformity of the GaN crystal are impaired. . More desirable is 2 to 10 mm.

  Further, during the growth of the GaN crystal, the rotation of the seed crystal 18 and the crucible 12 was controlled as shown in FIG. FIG. 2A shows the rotation mode of the crucible 12, and FIG. 2B shows the rotation mode of the seed crystal 18. As shown in FIG. 2A, the rotation mode of the crucible 12 is a positive gradually increasing section A in which the rotational speed increases linearly in the positive direction, a positive rotational section B in which the rotational speed is constant in the positive direction, and the rotational speed in the positive direction is linear. Decreasing positive gradually decreasing section C, stopping section D for stopping rotation, negative gradually increasing section E in which the rotational speed increases linearly in the negative direction, negative rotating section F in which the rotational speed is constant in the negative direction, and linearly decreasing the rotational speed in the negative direction This is a rotation mode in which a negative gradual decrease section G to be stopped and a stop section D to stop the rotation are set as one cycle. One cycle was 20 seconds, and the rotation speed in the positive rotation section B and the negative rotation section F was 10 rpm. Further, as shown in FIG. 2B, the rotation mode of the seed crystal 18 is a rotation mode in which the rotation mode of the crucible 12 is completely reversed. The negative increase period E, the negative rotation period F, the negative decrease period G, and the stop This is a rotation mode in which the section D, the positive gradual increase section A, the positive rotation section B, the positive gradual decrease section C, and the stop section D are set to 20 seconds per cycle.

  By rotating the crucible 12 and the seed crystal 18 in this way, the distribution of elements constituting the mixed melt 21 becomes uniform, and the concentration distribution of nitrogen dissolved in the mixed melt 21 becomes uniform. As a result, the thickness and crystallinity of the GaN crystal can be grown uniformly.

  The rotation speed (maximum rotation speed) of the crucible 12 and the seed crystal 18 is 10 rpm, and the rotation reversal period (one rotation mode period) is 20 seconds, but the rotation speed may be in the range of 1 to 30 rpm. It suffices that one period of the rotation mode is in the range of 8 seconds to 8 minutes. If it is this range, a mixed melt can be stirred efficiently. A more desirable rotation speed is 1 to 25 rpm, and one cycle of a more desirable rotation mode is 15 seconds to 7 minutes. Further, the stop section D and the sections where the rotational speed is gradually increased and decreased when the rotational speed is reversed (positive gradual increase section A, positive gradual decrease section C, negative gradual increase section E, negative gradual decrease section G) are necessarily provided. However, by providing these sections in the rotation mode, the turbulent flow in the mixed melt 21 can be prevented, but the crystal thickness and crystallinity can be made more uniform.

  As described above, the position of the seed crystal 18 is controlled by the holder 20 so that the distance from the GaN crystal surface to the gas-liquid interface is 10 mm or less, and the crucible 12 and the seed crystal 18 are rotated in the rotation mode shown in FIG. The GaN crystal was grown for 200 hours while controlling the temperature, and then the heating and pressurization were stopped to return to room temperature and normal pressure, the crystal growth of the GaN crystal was terminated, and the GaN grown on the seed crystal 18 and the seed crystal 18 The crystals were taken out and the adhered Na was removed with ethanol or the like. The thickness of the obtained GaN crystal was about 2.5 mm, and it was a good quality GaN crystal with uniform crystallinity and thickness.

  In Example 1, the distance from the GaN crystal surface to the gas-liquid interface is controlled to be 10 mm or less by moving the seed crystal in the vertical direction, but by moving the crucible in the vertical direction. Alternatively, the distance from the GaN crystal surface to the gas-liquid interface may be controlled to be 10 mm or less by moving both the crucible and the seed crystal in the vertical direction.

  In Example 1, a template substrate is used as a seed crystal, but a GaN free-standing substrate may be used.

  Moreover, although Example 1 was a manufacturing method of a GaN crystal, this invention is applicable also to manufacture of group III nitride semiconductors other than GaN, for example, AlGaN, InGaN, AlGaInN.

  The group III nitride semiconductor according to the present invention can be used as a growth substrate in the production of electronic devices made of group III nitride semiconductors (for example, light emitting devices such as LEDs and LDs, and field effect transistors such as HEMTs). . It can also be used as a material for photocatalysts and solar cells.

10: Pressure vessel 11: Reaction vessel 12: Crucible 13: Heating device 14, 16: Supply tube 15, 17: Exhaust tube 18: Seed crystal 19: Rotating device 20: Holder 191, 201: Base 192, 202: Rotating shaft 193, 203: Drive device

Claims (8)

A mixed melt containing at least a group III metal and an alkali metal and a seed crystal are held in a crucible, the mixed melt and a gas containing at least nitrogen are reacted, and a group III nitride semiconductor is added to the seed crystal. In the method for producing a group III nitride semiconductor crystal for crystal growth,
During the step of crystal growth of the group III nitride semiconductor crystal,
The distance from the surface of the group III nitride semiconductor crystal in the mixed melt to the gas-liquid interface between the mixed melt and the gas is maintained at 10 mm or less,
The seed crystal and the crucible are each independently rotated, and the rotation direction of the seed crystal is opposite to the rotation direction of the crucible.
A method for producing a group III nitride semiconductor crystal, characterized in that:   2. The method for producing a group III nitride semiconductor crystal according to claim 1, wherein a rotation speed of the seed crystal and the crucible is 1 to 30 rpm.   3. The method for producing a group III nitride semiconductor crystal according to claim 1, wherein the rotation directions of the seed crystal and the crucible are alternately reversed at a constant period.   4. The method for producing a group III nitride semiconductor crystal according to claim 3, wherein the period for switching the rotation direction is 8 seconds to 8 minutes.   The group III nitride semiconductor according to any one of claims 1 to 4, wherein a molar ratio of the group III metal to the entire mixed melt at the start of crystal growth is 15 to 30%. Crystal production method.   The method for producing a group III nitride semiconductor crystal according to any one of claims 1 to 5, wherein the pressure for crystal growth is 2.5 to 4.0 MPa.   The method for producing a group III nitride semiconductor crystal according to any one of claims 1 to 6, wherein the group III nitride semiconductor crystal is grown to a thickness of 1 mm or more.   The method for producing a group III nitride semiconductor crystal according to any one of claims 1 to 7, wherein a distance from the bottom of the crucible to the gas-liquid interface at the start of crystal growth is 20 mm or more. .

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