阅读说明：本技术 Iii族化合物基板的制造方法和iii族化合物基板 (Method for producing group III compound substrate, and group III compound substrate ) 是由 久保田芳宏 永田和寿 于 2020-05-01 设计创作，主要内容包括：本发明的III族化合物基板的制造方法,其特征在于：其是通过气相生长法使III族化合物的晶体(1)在载置并固定于基座(2)的晶种(3)上生长的III族化合物基板的制造方法,在基座(2)和晶种(3)的至少一者的构件中使用可剥离的具有劈开性的物质。III族化合物基板,其特征在于：其是通过本发明的III族化合物基板的制造方法制造的。根据本发明,可提供III族化合物基板的制造方法和通过该制造方法制造的基板,该制造方法可有效利用气相生长法的特长、即高成膜速度的特长,同时以低成本得到更高品质的大型GaN晶体基板。(The method for producing a group III compound substrate of the present invention is characterized in that: a method for producing a group III compound substrate by growing a crystal (1) of a group III compound on a seed crystal (3) placed on and fixed to a susceptor (2) by a vapor phase growth method, wherein a substance having a cleavage property which can be peeled off is used for at least one member of the susceptor (2) and the seed crystal (3). A group III compound substrate, characterized in that: which is produced by the method for producing a group III compound substrate of the present invention. According to the present invention, a method for producing a group III compound substrate, which can obtain a high-quality large GaN crystal substrate at low cost while effectively utilizing the characteristics of the vapor phase growth method, that is, the characteristics of a high film formation rate, and a substrate produced by the production method can be provided.)

A method for producing a group III compound substrate, characterized in that: which is a method for producing a group III compound substrate by growing a crystal of a group III compound on a seed crystal placed and fixed on a susceptor by a vapor phase growth method,

a substance having a cleavage property which can be peeled is used for at least one member of the base and the seed crystal.

2. The method for producing a group III compound substrate according to claim 1, wherein: at least the surface of the susceptor on which the seed crystal is placed is made of the peelable cleavage substance,

the strippable cleavage substance is Pyrolytic Boron Nitride (PBN).

3. The method for producing a group III compound substrate according to claim 1 or 2, wherein: the strippable cleavage substance is a composite of Pyrolytic Boron Nitride (PBN) and carbon.

4. The method for producing a group III compound substrate according to any one of claims 1 to 3, wherein: the seed crystal is composed of the peelable cleavage-promoting substance,

the peelable substance having cleavage property is SCAM, namely ScAlMgO₄And (4) crystals.

5. The method for producing a group III compound substrate according to any one of claims 1 to 4, comprising:

a 1 st crystal growth step of growing a crystal of a group III compound on the seed crystal at a 1 st crystallization rate; and

a 2 nd crystal growth step of, after the 1 st crystal growth step, growing a crystal of a group III compound on the seed crystal at a 2 nd crystallization rate lower than the 1 st crystallization rate.

6. The method of manufacturing a group III compound substrate according to claim 5, comprising: a 3 rd crystallization step of growing a crystal of a group III compound on the seed crystal at a 3 rd crystallization rate between the 1 st crystal growth step and the 2 nd crystallization step,

in the 3 rd crystallization step, the 3 rd crystallization rate is gradually and/or continuously changed from the 1 st crystallization rate to the 2 nd crystallization rate.

7. The method for producing a group III compound substrate according to any one of claims 1 to 6, wherein: the group III compound is gallium nitride, GaN.

A group III compound substrate, characterized in that: the group III compound substrate is produced by the method for producing a group III compound substrate according to any one of claims 1 to 7.

Technical Field

The present invention relates to high-quality AlN and Ga₂O₃A method for producing a group III compound substrate such as GaN, and a substrate therefor, particularly a GaN crystal substrate.

Background

Crystalline AlN and Ga₂O₃And a substrate of a group III compound such as GaN has a wide band gap, has a very short wavelength light emitting property, has a high withstand voltage, and has excellent high-frequency characteristics. Therefore, substrates of group III compounds are expected to be used in devices such as lasers, Schottky diodes (Schottky diodes), power devices, and high-frequency devices. However, it is difficult to grow high-quality and large-diameter crystals of these group III compounds, and the use of group III compound substrates is limited.

For example, although bulk GaN substrates obtained by growing GaN crystals in a liquid such as liquid ammonia or Na flux generally have high quality in vertical GaN substrates, it is difficult to increase the diameter of the substrates to a large size. On the other hand, in the Metal Organic Chemical Vapor Deposition (MOCVD) method or the hydride vapor deposition (HVPE, THVPE, etc.) method in which crystal growth is performed in a vapor phase, GaN thin films having a large diameter are obtained by heteroepitaxial growth of GaN on a substrate such as a sapphire substrate, a GaAs substrate, or an AlN substrate. However, in the heteroepitaxial growth method, if the film thickness is increased in order to obtain a high-quality substrate, lattice defects, warpage, and cracking are likely to occur.

For example, non-patent document 1 describes: a plurality of small-diameter GaN substrates prepared by the Na flux method were bonded to a Pyrolytic Graphite (PG) base in a honeycomb shape, and GaN was grown thereon by the HVPE method using this as a seed substrate, thereby obtaining a large-diameter GaN substrate.

Non-patent document 2 describes the following production method: with SCAM (ScAlMgO)₄) The (0001) substrate is a seed crystal on which epitaxial growth of GaN is performed by MOVPE (organometallic vapor phase epitaxy).

Patent document 1 describes the following method: GaN crystals are epitaxially grown on a sapphire substrate, the crystals are cut into a honeycomb shape, and the honeycomb shape is attached to a base such as PG with an adhesive containing a heat-resistant ceramic and an inorganic polymer as main components, and the GaN crystals are grown to a larger size and a thicker film by HVPE as seed crystals.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 6203460;

non-patent document

Non-patent document 1: phys. Status Solidi B254, No.8, 1600671 (2017);

non-patent document 2: phys. Status Solidi A214, No.9, 1600754 (2017).

Disclosure of Invention

Problems to be solved by the invention

In the above-mentioned prior art, there are also 2 common problems. That is, even if the GaN crystal grown is cooled after growth, and the produced GaN crystal is peeled off and recovered from the seed crystal, the both are strongly bonded, and it is difficult to obtain the target GaN crystal and recover the expensive seed crystal at high yield. When the grown GaN crystal is forcibly peeled off from the seed crystal of sapphire, GaN or the like and recovered, the GaN crystal itself produced at this time is discarded, or the produced GaN crystal is easily damaged by a subsequent step or an operation at the time of processing. Further, the seed crystal adheres not only to the produced GaN but also strongly to the susceptor, and applies strong thermal stress to the produced GaN crystal, which becomes a factor of warping or cracking of the produced GaN crystal.

The present invention has been made in view of the above circumstances, and an object thereof is to provide: a method for producing a group III compound substrate such as high-quality AlN or GaN crystal having a large diameter and a large thickness, and a group III compound substrate, particularly a GaN substrate, obtained by the method.

Means for solving the problems

In order to achieve the above object, the present invention provides a method for producing a group III compound substrate and a substrate produced by the method.

(1) A method for producing a group III compound substrate, comprising: the method for producing a group III compound substrate comprises growing a crystal of a group III compound on a seed crystal placed on and fixed to a susceptor by vapor phase growth, wherein a substance having a cleavage property which can be peeled off is used as at least one member of the susceptor and the seed crystal.

(2) The method for producing a group III compound substrate according to the item (1), wherein: at least the surface of the susceptor on which the seed crystal is placed is made of the peelable cleavage-promoting substance, and the peelable cleavage-promoting substance is Pyrolytic Boron Nitride (PBN).

(3) The method for producing a group III compound substrate according to the above (1) or (2), wherein: the strippable cleavage substance is a composite of Pyrolytic Boron Nitride (PBN) and carbon.

(4) The method for producing a group III compound substrate according to any one of the above (1) to (3), wherein: the seed crystal is composed of the peelable cleavage-promoting substance,

the peelable substance having cleavage property is SCAM (ScAlMgO)₄) And (4) crystals.

(5) The method for producing a group III compound substrate according to any one of the above (1) to (4), comprising: a 1 st crystal growth step of growing a crystal of a group III compound on the seed crystal at a 1 st crystallization rate; and a 2 nd crystal growth step of, after the 1 st crystal growth step, growing a crystal of a group III compound on the seed crystal at a 2 nd crystallization rate lower than the 1 st crystallization rate.

(6) The method for producing a group III compound substrate according to item (5) above, comprising: and a 3 rd crystallization step of growing a crystal of a group III compound on the seed crystal at a 3 rd crystallization rate between the 1 st crystal growth step and the 2 nd crystallization step, wherein in the 3 rd crystallization step, the 3 rd crystallization rate is gradually and/or continuously changed from the 1 st crystallization rate to the 2 nd crystallization rate.

(7) The method for producing a group III compound substrate according to any one of the above (1) to (6), wherein: the group III compound is gallium nitride (GaN).

(8) A group III compound substrate, characterized in that: the group III compound substrate is produced by the method for producing a group III compound substrate according to any one of the above (1) to (7).

Effects of the invention

According to the present invention, a large group III compound substrate of higher quality can be obtained at low cost while effectively utilizing the characteristic of the vapor phase growth method, i.e., the characteristic of high film formation rate. That is, since an extremely thick group III compound substrate having a large diameter and no variation can be produced, a group III compound substrate having a large diameter, which is excellent in crystal characteristics of the substrate and low in cost, can be easily obtained.

Drawings

Fig. 1 is a schematic view for explaining a method for producing a group III compound substrate according to an embodiment of the present invention.

Fig. 2 is a schematic view for explaining an example of a method for producing a group III compound substrate according to an embodiment of the present invention.

Detailed Description

The method for producing a group III compound substrate of the present invention is characterized in that: the method for producing a group III compound substrate comprises growing a crystal of a group III compound on a seed crystal placed on and fixed to a susceptor by a vapor phase growth method, wherein a substance having a cleavage property which can be peeled off is used as at least one member of the susceptor and the seed crystal. For example, a part or the whole of the base may be formed of a peelable substance having cleavage property. In addition, a part or the whole of the seed crystal may be composed of a substance having a cleavage property which can be peeled. Hereinafter, a method for manufacturing a group III compound substrate, particularly a GaN substrate, and a substrate thereof according to the present invention will be described.

The production method of the present invention is directed to AlN and Ga₂O₃Group III compounds such as GaN are effective, and are particularly suitable for GaN crystal growth, and among them, the group III compounds are used in vapor phase growth methods, particularly hydride vapor phase growth methods (HVPE method, THVPE method, etc.), which have a high crystal growth rate and are suitable for the production of large-diameter and thick articles.

In the conventional technique of the hydride vapor phase growth method (HVPE method, THVPE method, etc.) up to now, after growing a GaN crystal, the GaN crystal is cooled, and even if it is desired to peel off and recover the produced GaN crystal from a seed crystal such as sapphire or GaN, the both are strongly bonded, so that it is very difficult to obtain a target GaN crystal in a high yield or recover an expensive seed crystal without discarding the same. When the grown GaN crystal is forcibly peeled off from a seed crystal such as sapphire or GaN and recovered, an excessive force is applied, and the expensive GaN crystal is often damaged or damaged. Further, the seed crystal adheres not only to the produced GaN crystal but also strongly to the base structure, and exerts strong thermal stress on the GaN crystal after reaction and cooling, which becomes a significant cause of various characteristic deteriorations, warpage, and cracking. In particular, these phenomena become more remarkable when growing a large-diameter or thick crystal, and become a serious bottleneck for achieving high characteristics and low cost of the GaN substrate.

The present inventors have made extensive studies and as a result, have solved the above-mentioned problems by using a peelable cleavage substance for one or both of the seed crystal and the susceptor on which the seed crystal is placed. That is, if a releasable substance having cleavage property is used for the seed crystal, the seed crystal can be easily released from the cleavage plane of the seed crystal when the generated GaN crystal is released, and the generated GaN crystal and the seed crystal can be easily recovered. Further, by using a substance having a cleavage property which can be peeled in the susceptor, the susceptor can be easily peeled from the cleavage plane of the susceptor when the produced GaN crystal is peeled, and the produced GaN crystal and the seed crystal can be easily recovered.

Thus, the characteristic of the vapor phase growth method, i.e., the characteristic of a high film formation rate, can be effectively utilized, and a large-sized GaN crystal substrate of higher quality can be obtained at low cost. That is, since an extremely thick GaN crystal substrate having a large diameter and no variation can be produced, a GaN substrate having a large diameter, which is excellent in crystal characteristics of the substrate and low in cost, can be easily obtained.

At least the surface of the susceptor on which the seed crystal is placed may be made of the above-mentioned peelable cleavage-promoting substance. Therefore, the entire base does not need to be made of the peelable and cleavable substance described above.

The substance having cleavage properties for the base is preferably a layered substance. By using the layered material for the susceptor, the susceptor can be easily peeled between the mesh planes of the layer structure of the layered material when peeling the produced GaN crystal, and the produced GaN crystal and the seed crystal can be more easily recovered. Further, by using a substance having a layered substance in the susceptor, thermal stress generated by adhesion of the produced GaN crystal to the susceptor can be appropriately absorbed by the interlayer, or can be relieved by interlayer peeling.

By using a substance having a cleavage property which can be peeled in at least one member of the susceptor and the seed crystal, a GaN crystal can be obtained at a high yield without causing warpage, cracking, or the like even in a GaN crystal having a large diameter and a thick material which has been difficult so far, and the seed crystal can be repeatedly used because the recovery of an expensive seed crystal is easy.

The "peelable substance having cleavage property" means a substance cleaved by mechanical impact to the extent that the group III compound substrate and the seed crystal are not broken or damaged, or a substance cleaved by thermal stress generated by a difference in thermal expansion coefficient between the group III compound substrate and the seed crystal.

Further, it is preferable to first fabricate the GaN base (handle) substrate portion 11 at a relatively high crystal growth rate and then thicken the GaN crystal main body portion 12 at a low rate (see fig. 1). Thus, the GaN substrate (handle) portion 11 functions as the following (i) to (iv): (i) a barrier layer for impurity diffusion from the seed crystal 3 or the susceptor 2; and (ii) a "sacrificial layer" that reduces crystal defects of the target GaN crystal main body portion 12 due to the nature of crystal growth in which thicker the crystal growth build-up is, the more crystal defects are reduced in the upper layer portion thereof; further, (iii) a "protective layer" for preventing mechanical damage during peeling after crystal growth or in a subsequent processing step; or (iv) handling of the substrate during handling/transportation. In this way, the target GaN crystal main body portion is preferably grown at a lower rate, and deterioration of characteristics such as lattice defects and variation of other characteristics can be suppressed.

From the price, to the reaction gas (GaCl )₃、NH₃) From the viewpoint of corrosion resistance and contamination of impurities, the strippable and cleavable substance used for the base is preferably Pyrolytic Boron Nitride (PBN) which is a layered compound having high purity and is not attacked by reaction gases, and from the viewpoint of cost (large size and high strength), a PBN which is easily delaminated between layers and is produced by intentionally weakening the interlayer bonding strength of the PBN, or a composite of the PBN and carbon is more preferable. Among the boron nitrides, hexagonal boron nitride is a layered compound.

In the case of forming a PBN coating on the surface of a carbon substrate to produce a PBN/carbon composite, for example, the method described in Japanese examined patent publication (Kokoku) No. 4-79992 can be used. In this case, the PBN layer can be formed by increasing or decreasing the furnace internal pressure in a pulse manner during the formation of the PBN film in the chemical vapor deposition furnace, and the bonding force between the surfaces of the PBN layer that are bonded to each other in a planar layered structure becomes weak. By appropriately inserting such a layer having a weak bonding force during film formation, a PBN film which can be easily delaminated from the layer can be formed.

From the viewpoints of close lattice constant and thermal expansion coefficient to GaN crystal, resistance to raw material gas, relatively low cost, and easiness of separation/recovery from the produced GaN crystal, it is preferable to use SCAM (ScAlMgO) as the substance having cleavage property and capable of being separated from the seed crystal₄) The crystal is preferably cleaved SCAM (ScAlMgO)₄) Or a substrate obtained by laminating a plurality of such substrates in a crystal orientation. From counter reaction gases (GaCl )₃、NH₃) SiO can be used from the viewpoint of corrosion resistance, contamination of impurities, etc₂Or AlN coated on the surface of the substrate.

In the present invention, when the base on which the seed crystal is placed is a substance having a cleavage property which can be peeled, a substance having a cleavage property which can be peeled can be used for the seed crystal. In this case, a GaN substrate or the like selected from the manufacturing methods of MOCVD method, Na flux method, and liquid ammonia method may be used for the seed substrate.

In the present invention, when the seed crystal is a peelable substance having cleavage property, a peelable substance having cleavage property can be used for the base. In this case, a GaN substrate itself, ceramics such as Pyrolytic Graphite (PG) and corundum, or the like may be used as the susceptor. PG is a layered substance and has cleavage properties, but is not easily peeled off because the bonding between the web planes of the layer structure is strong.

In the present invention, for the above reasons, it is preferable to first fabricate the GaN base (handle) substrate portion 11 at a relatively high crystal growth rate and then thicken the GaN crystal main body portion 12 at a low rate. In view of more economical and efficient aspects and the suppression of stress generation in the produced GaN crystal, the improvement of characteristics, etc., it is particularly preferable to gradually and/or continuously decrease the rate a plurality of times when changing from a high rate to a low rate (see crystal growth rate transition portion 13 in fig. 1).

Examples

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[ example 1]

A mat-like heat insulator of alumina was placed in a stainless steel reactor (inner surface pre-sprayed with extremely thin zirconia) having a water-cooled jacket and an exhaust port and having an inner diameter of 1500mm × height 1800mm, and a cylindrical heating device (inner diameter 1000mm × height 1300mm) having a rod-like SiC heater and a gas supply pipe (see reference numeral 6 in FIG. 2) (the same material as the reactor, center tube 61; inner diameter: 6; see FIG. 2) were provided inside the reactorϕ30mm, 2 nd tube 62; inner diameterϕ40mm, outermost tube 63; inner diameterϕ50 mm). On the other hand, prepareϕ520mm PBN coatingGraphite susceptor revolution jig (see reference numeral 5 in fig. 2) which houses the jig at 120 ° intervalsϕA 3-piece base made of PBN (manufactured by changing the internal pressure of a furnace in a pulse manner during the manufacture of PBN) having interlayer peeling properties of 170mm (see reference numeral 2 in FIG. 2). The susceptor surface was processed into a brick shape from 2-inch SCAM crystals to be a seed substrate (see reference numeral 3 in fig. 2), an alumina-based adhesive material (see reference numeral 4 in fig. 1) was attached to the back surface, the substrate was bonded into a 6-inch disk shape, and then heated to 1380 ℃ by a heater, and while rotating at 10rpm, a susceptor 2 was revolved by a susceptor revolution jig 5, and each of 3 susceptors 2 was rotated at 30rpm by the force of its revolution gear, and after confirming that the temperature and the rotation were stable, GaCl was supplied to the inside of the reactor from a central tube 61 of a triple tube₃Gas, NH supplied from outermost pipe 63₃Gas, N from the pipe 62 between the central pipe and the outermost pipe₂Gas, the THVPE reaction starts.

Initially, as a high rate of crystal growth, at about 300AμAfter 1 hour of reaction at a rate of m/hr (refer to symbol 11 in FIG. 1), the raw material gas was gradually reduced for 2 hours, and the growth rate was adjusted to finally reach about 100μAfter m/hour (see reference numeral 13 in FIG. 1), a low-speed reaction was carried out for 45 hours (see reference numeral 12 in FIG. 1).

After cooling, the obtained GaN crystal is easily peeled off from the SCAM crystal by the cleavage property of the seed SCAM, and the seed SCAM is recovered and reused. The peeled GaN crystal was subjected to thermal stress absorption by interlayer peeling of the layered PBN base, and therefore, was not substantially warped, and thus, it was possible to process the crystal by barrel grinding without modification, and a GaN crystal composed of a high-speed reaction part, a speed transition part, and a low-speed reaction part was producedϕ6 inches by 5mm thick base substrate (original substrate).

The base material substrate was sliced and polished appropriately from the front surface side of the low-speed reaction part to obtain a thickness 625μm, a smooth GaN substrate. For the reaction analysis, the following analysis was performed on the GaN substrate including the high-speed portion (see reference numeral 11 in fig. 1) together with the GaN substrate of the low-speed reaction portion that has been produced. The high-speed reaction portion is used as a control substrate during processing, a "protective layer" for reducing mechanical damage, and a protection layer for preventing mechanical damageA "barrier layer" for preventing contamination with impurities from an adhesive or the like and a "sacrificial layer" for reducing crystal defects function.

In any 3 points of the Full Width at Half Maximum (FWHM: Full Width at Half Maximum) of the X-ray rocking curve of the (100) surface of the GaN substrate processed by the above-mentioned low-speed reaction portion (see reference numeral 12 in fig. 1), the average was 31 arcsec (arcsec) and the variation was 3 arcsec (arcsec), and the crystallinity was good. On the other hand, the GaN substrate including the high-speed portion (see reference numeral 11 in fig. 1) was 448 arc seconds (arcsec) and the variation was 84 arc seconds (arcsec). Incidentally, as a result of chemical analysis of the surface of each substrate, although metal contamination of the GaN substrate in the low-speed reaction part 12 was below the detection limit, it was considered that a very small amount of metals such as Mg, Al, Si, and Fe was mixed into the lower part side (seed crystal side and base side) of the GaN substrate including the high-speed reaction part 11, and the metals were derived from the seed crystal and the alumina-based adhesive material used.

Further, stacking faults were observed under a monochromatic cathodoluminescence image, and as a result, no stacking faults were observed in the surface layer of the produced GaN substrate. On the other hand, stacking faults were seen in the GaN substrate including the high-speed portion 11, and many stacking faults were observed particularly in the high-speed portion 11. This shows that: the high-speed portion 11 functions as a trap layer for impurities, or a sacrificial layer for defects. The above results show that: the produced GaN crystal substrate is a good, uniform GaN crystal substrate with no warpage and no deviation. The effect of this embodiment shows: (1) one or both of the seed crystal and the base structure on which the seed crystal is placed are made of a substance having a cleavage property and/or a layer property which can be peeled; further, (2) the synergistic effect of the substrate portion 11 and the main GaN crystal portion 12 is large, which is produced by making the substrate of GaN (handle) at a relatively high crystal growth rate first and then making the thick film of the main GaN crystal portion at a low rate.

[ comparative example ]

In example 1, crystal growth was performed under exactly the same conditions except that the seed crystal was changed from SCAM crystal to 2-inch GaN substrate made of removable Na flux having no cleavage property, and the susceptor was changed to ceramic having removable corundum having no cleavage property. As a result, after the THVPE reaction, although cooling was performed to take out the internal product, the GaN and the susceptor fused together, and the produced GaN and the expensive seed substrate were crushed into powder and could not be recovered.

[ example 2]

Except that the seed substrate of the SCAM of example 1 was changed to a 2-inch GaN substrate manufactured by using a strippable Na flux having no cleavage property, and the reaction gas was changed from GaCl₃The crystal growth reaction was carried out under the same conditions except that the gas was changed to GaCl so that the HVPE method was changed from THVPE. The reaction was carried out at the same linear speed as in example 1 in terms of Ga amount. After cooling, the obtained GaN crystal was integrated with the seed crystal, and the GaN crystal was easily peeled off from the layered PBN base. The thermal stress during cooling is absorbed by delamination, and cracks are not generated, and warpage is not substantially generated. In the same manner as in example 1, any 3 points in the Full Width at Half Maximum (FWHM) of the X-ray rocking curve of the (100) plane of the produced GaN substrate were 25 arc seconds (arcsec) on average and 3 arc seconds (arcsec) off set. The analytical value of the metal impurities is below the detection limit. In addition, lamination defects were observed by monochromatic cathodoluminescence images, with the results: substantially no stacking faults were observed in the surface layer of GaN. The above measurements and observations show that: the obtained GaN crystal was a very uniform and good crystal substrate without variation.

[ example 3]

In example 1, about 100 a from the beginningμThe crystal growth was carried out under exactly the same conditions except that the crystal growth was carried out at a low rate of m/hr for 50 hours and that a susceptor made of Pyrolytic Graphite (PG) which has cleavability but is difficult to be peeled was used as the susceptor. The obtained GaN crystal can be easily peeled off from the SCAM and PG bases of the seed crystal, and the SCAM can be recovered and reused. The peeled GaN crystal cannot sufficiently absorb the thermal stress of the GaN crystal because of the weak interlayer peeling property of the PG-made layered base, and a warp of several millimeters occurs. However, no cracking occurred. The edge is slightly corrected and is processed into the shape of a cylinder by cylinder grindingϕ6 inches.

Description of the symbols

1: a GaN substrate;

2: a base;

3: seed crystals;

4: an adhesive;

5: a base revolution fixture;

6: a gas supply pipe;

11: a substrate (handle) portion;

12: a GaN crystal body portion;

13: a crystal growth rate transition section.