JP2008297180A - METHOD FOR GROWING GaN CRYSTAL AND GaN CRYSTAL SUBSTRATE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a GaN crystal small in the size of a reversed-polarity crystalline region and low in its density and to provide a GaN crystal substrate. <P>SOLUTION: The method for growing a GaN crystal is one comprising the step of preparing a GaN substrate 10 containing a main crystalline region 11 and a plurality of reversed-polarity crystalline regions 12 reversed in polarity in the [0001] direction with respect to the main crystalline region and the step of growing a GaN crystal 20 by a vapor phase deposition method on the (0001) Ga main face 10g of the GaN substrate 10, wherein the GaN crystal 20 is grown so that it contains a first crystalline region 21 which grows on the main crystalline region 11 and a plurality of second crystalline regions 22 each of which grows on the reversed-polarity region 12, the second crystalline regions 22 are reversed in polarity in the [0001] direction with respect to the first crystalline region 21, and the first crystalline region 21 is higher in a crystal growth rate than the second crystalline regions 22 so as to allow the second crystalline regions 22 to be embedded therein. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a GaN crystal growth method and a GaN crystal substrate obtained by the method.

  GaN crystals are light-emitting elements such as light-emitting diodes and laser diodes, electronic elements such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (high electron mobility transistors), temperature sensors, pressure sensors, radiation sensors, and visible-ultraviolet light detection. Widely used for semiconductor sensors such as ceramics, SAW devices (surface acoustic wave elements), vibrators, resonators, MEMS (micro-electromechanical system) parts, and substrates of devices such as piezoelectric actuators.

  For such GaN crystals, it is difficult to obtain a large free-standing substrate. Therefore, a GaN-based crystal thin film is grown on a heterogeneous substrate having a chemical composition different from that of GaN such as a sapphire substrate or a SiC substrate, whereby a light emitting element such as a blue LED is manufactured. Specifically, an amorphous layer called a low-temperature buffer layer is grown on a heterogeneous substrate at a low temperature of about 500 ° C. Next, when the temperature is raised to 1000 ° C., the amorphous layer is crystallized, and crystals are grown on the crystallized low-temperature buffer layer. As the crystal growth method, a vapor phase method such as HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, MBE (molecular beam epitaxy) method or the like is preferably used from the viewpoint of easy epitaxial growth. From the viewpoint of rapid growth, the HVPE method is more preferably used.

In the case of growth of a GaN-based crystal thin film using such a heterogeneous substrate, dislocations having a density of 1 × 10 ⁸ cm ⁻² or more exist in the GaN-based crystal thin film. In a light emitting device having a relatively low current density such as a blue LED, the dislocation density of the GaN-based crystal thin film is not a problem. However, in devices that are strongly affected by dislocations such as light emitting elements such as ultraviolet LEDs and power electronic devices and require low dislocations, it is necessary to reduce the dislocation density of the GaN-based crystal thin film.

For this reason, various methods for reducing the dislocation density of GaN-based crystals have been studied and proposed. For example, it is known that the dislocation density of a crystal is reduced by growing a thick crystal of several millimeters even on a different substrate. Xueping Xu and five others, Growth and characterization of low defect GaN by hydride vapor phase epitaxy, J. Crystal Growth, 246, (2002), p223-229 (hereinafter referred to as non-patent document 1) can be reduced to about 1 × 10 ⁶ cm ⁻² by growing a crystal of about 1 mm. Is disclosed.

  Akira Usui, 3 others, Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy, Jpn. J. Appl. Ptys., 36, (1997), L899-L902 Discloses a method for reducing the dislocation density by controlling the propagation direction of dislocations during crystal growth using a mask having openings.

Although the dislocation density of the GaN-based crystal could be reduced to about 1 × 10 ⁶ cm ⁻² by the methods of Non-Patent Document 1 and Non-Patent Document 2 described above, an ultraviolet LED using such a GaN-based crystal was used. The characteristics of the light-emitting elements, power electronic devices, etc. did not improve much.
Xueping Xu, 5 others, Growth and characterization of low defect GaN by hydride vapor phase epitaxy, J. Crystal Growth, 246, (2002), p223-229 Akira Usui, 3 others, Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy, Jpn. J. Appl. Ptys., 36, (1997), L899-L902

  Based on the following examination, we have found that many macro defects other than dislocations are formed in the GaN-based crystal obtained by the methods of Non-Patent Document 1 and Non-Patent Document 2 described above.

  That is, pits derived from crystal defects are formed by etching the main surface (for example, (0001) Ga face) of a GaN-based crystal with alkali. For example, when a mirror-polished (0001) Ga surface of a GaN crystal is etched with a KOH aqueous solution (KOH concentration: 2 mol / liter) at a liquid temperature of 50 ° C. for about several tens of minutes, only the portion where crystal defects exist is about several μm. A recess having a rough surface is formed.

  Further, when the (0001) Ga surface of the GaN crystal is etched with KOH melt, NaOH melt, or a mixed melt thereof, a plurality of hexagonal columnar recesses are formed. The six side surfaces of this hexagonal column are M-planes. Further, the depth D of the hexagonal columnar recess varies depending on the etching conditions such as the type of the etching solution, the etching temperature, and the etching time.

  Here, the GaN crystal is a crystal having a polarity in the [0001] direction (c-axis direction), and has a characteristic that the (000-1) N plane is more easily etched than the (0001) Ga plane. Considering the characteristics of the GaN crystal, when the (0001) Ga face of the Ga crystal is etched as described above, a plurality of hexagonal columnar recesses that are partially generated are derived from the (000-1) N face. I know that there is. That is, it can be seen that a plurality of (000-1) N planes appear partially on the (0001) Ga plane of the GaN crystal. This indicates that the GaN crystal has a plurality of polarity-inverted crystal regions in which the polarity in the [0001] direction is inverted with respect to the main crystal region and the main crystal region.

  When the (0001) Ga surface of the GaN crystal is etched with KOH melt, NaOH melt, or a mixed melt thereof, a plurality of hexagonal pyramid-shaped recesses are formed in addition to the plurality of hexagonal columnar recesses. . Such hexagonal pyramid-shaped recesses are derived from dislocations, and can be clearly distinguished from the recesses derived from the polarity-reversal crystal region by the difference in the shape of the recesses.

  Based on the above studies, we have found that a GaN crystal manufactured by the methods of Non-Patent Document 1 and Non-Patent Document 2 has a polarity inversion crystal region formed as a large number of macro defects other than dislocations, and a device including such a GaN crystal. It was found that the improvement of the characteristics of is suppressed.

  Based on the above findings, an object of the present invention is to provide a method for growing a GaN crystal and a GaN crystal substrate having a small polarity-reversed crystal region and a low density.

  We examine in detail the growth of GaN crystal on the GaN substrate, and the growth rate of the first crystal region of the GaN crystal growing on the main crystal region of the GaN substrate is set on the polarity reversal crystal region of the GaN substrate. By making the growth rate higher than the growth rate of the second crystal region of the growing GaN crystal (this is a polarity reversal crystal region in which the polarity in the [0001] direction is reversed with respect to the first crystal region), The first crystal region grows so as to embed the second crystal region, which is a polarity reversal crystal region, without forming irregularities or through holes on the main surface as shown in JP-A-2004-221480 on the substrate. Thus, a GaN crystal having a small second crystal region (polarity reversal crystal region) and a low density can be produced.

  The present invention provides a step of preparing a GaN substrate including a main crystal region and a plurality of polarity-inverted crystal regions whose polarities in the [0001] direction are reversed with respect to the main crystal region, A method for growing a GaN crystal including a step of growing a GaN crystal on a surface by a vapor phase method, wherein the GaN crystal grows on a first crystal region and each polarity-inverted crystal region that grow on a main crystal region, respectively. The second crystal region has a polarity reversed in the [0001] direction with respect to the first crystal region, and the first crystal region has the second crystal region A method for growing a GaN crystal characterized in that the crystal growth rate is higher than that of the region, and the second crystal region is grown so as to be embedded.

In the GaN crystal growth method according to the present invention, the square root of the area of one second crystal region on the crystal growth surface when the crystal growth thickness T ₁ mm of the GaN crystal is R ₁ μm, and the crystal growth height of the GaN crystal is when the square root of the area of one second crystal regions thereof and R ₂ [mu] m in a crystal growth surface in the case of the T ₂ mm, increase of growth thickness of the GaN crystal (T ₂ -T ₁₎ thereof to mm The ratio (R ₁ -R ₂ ) / (T ₂ -T ₁ ) of the reduction amount (R ₁ -R ₂ ) μm of the square root of the area of one second crystal region can be 10 μm / mm or more.

The method for growing a GaN crystal according to the present invention further includes a step of forming a recess in the polarity reversal crystal region in the (0001) Ga main surface of the GaN substrate after the step of preparing the GaN substrate, wherein the recess is formed. And a step of growing a GaN crystal on the (0001) Ga plane. Here, the (0001) Ga surface after the formation of the concave portion has a concave surface and a convex surface, and the square root of the area of one second crystal region of the GaN crystal on the concave surface of the GaN substrate is R _S μm, When the square root of the area of the one second crystal region in the crystal growth surface of the GaN crystal lying in the same plane as the convex surface of the second is R _O μm, the square root of the area of the one second crystal region due to the concave portion Decrease amount (R _S −R _O ) μm can be set to 10 μm or more. Further, the depth _D μm of the concave surface from the convex surface can be three times or more the square root R _S μm of the area of the polarity inversion crystal region.

  The present invention is also a GaN crystal substrate obtained by the above growth method.

  According to the present invention, it is possible to provide a GaN crystal growth method and a GaN crystal substrate in which the size of the polarity inversion crystal region is small and the density thereof is low.

(Embodiment 1)
One embodiment of a method for growing a GaN crystal according to the present invention is described with reference to FIGS. 1 and 2. A step of preparing the GaN substrate 10 including the polarity reversal crystal region 12 and a step of growing the GaN crystal 20 on the (0001) Ga main surface 10g of the GaN substrate 11 by a vapor phase method are included. Here, the GaN crystal 20 includes a first crystal region 21 that grows on the main crystal region 11 and a plurality of second crystal regions 22 that grow on the polarity inversion crystal regions 12 respectively. Further, the polarity of the [0001] direction of the second crystal region 22 is reversed with respect to the first crystal region 21, and the first crystal region 21 has a crystal growth rate compared to the second crystal region 22. It grows so as to fill the second crystal region 22.

  With reference to FIGS. 1 and 2A, the GaN crystal growth method of the present embodiment has a plurality of polarities in which the polarity in the [0001] direction is reversed with respect to the main crystal region 11 and the main crystal region 11. A step of preparing a GaN substrate 10 including the inversion crystal region 12. The GaN substrate 10 including the main crystal region 11 and the polarity inversion crystal region 12 is generally grown by the ELO method or the facet growth method, and the dislocation density of the main crystal region is low. For this reason, a GaN crystal having a low dislocation density can be grown.

  Since the main crystal region 11 and the polarity inversion crystal region 12 of the GaN substrate 10 have different chemical characteristics, they can be easily identified by observation with an optical microscope, for example, by etching with an aqueous NaOH solution. Here, a plurality of polarity reversal crystal regions 12 are randomly present in the GaN substrate 10, and the shape of the polarity reversal crystal regions 12 appearing on the (0001) Ga main surface of the GaN substrate 10 is indefinite.

The GaN crystal growth method of this embodiment includes a step of growing the GaN crystal 20 on the (0001) Ga main surface 10g of the GaN substrate 11 by a vapor phase method.
On the (0001) Ga main surface 10g of the GaN substrate 10, the (0001) Ga surface 11g of the main crystal region 11 and the (0001) N surface 12n of the polarity reversal crystal region 12 appear, and on the (000-1) N surface 10n. The (000-1) N face 11n of the main crystal region 11 and the (000-1) Ga face 12g of the polarity inversion crystal region 12 appear.

  Accordingly, the first crystal region 21 of the GaN crystal 20 grown on the main crystal region 11 of the (0001) Ga main surface 10 g of the GaN substrate 10 takes over the polarity of the main crystal region 11. In addition, the second crystal region 22 of the GaN crystal 20 grown on the polarity reversal crystal region 12 of the (0001) Ga main surface 10 g of the GaN substrate 10 takes over the polarity of the polarity reversal crystal region 12. That is, the second crystal region 22 has a polarity in which the [0001] direction is reversed with respect to the first crystal region 21. Therefore, the (0001) Ga plane of the first crystal region 21 and the (0001) N plane of the second crystal region 22 appear on the crystal growth surfaces 20a, 20b, 20g of the GaN crystal 20.

  Here, the vapor phase method used in the present embodiment is not particularly limited, but HVPE method, MOCVD method, MBE method and the like are preferable from the viewpoint that epitaxial growth is possible to reduce the dislocation density. Of these vapor phase methods, the HVPE method is particularly preferred from the viewpoint of high crystal growth rate.

  In the GaN crystal growth method of this embodiment, the first crystal region 21 has a higher crystal growth rate than the second crystal region 22 and grows so as to embed the second crystal region 22. For this reason, the GaN crystal 20 having a small size and a low density of the second crystal region 22 which is a polarity inversion crystal region is obtained. By using such a GaN crystal, a device having high characteristics can be obtained.

Here, in order to make the crystal growth rate of the first crystal region 21 higher than the crystal growth rate of the second crystal region 22, in the HVPE method, the partial pressure of gallium source gas (GaCl gas) is 1 × 10 ³ Pa. ˜1 × 10 ⁴ Pa, nitrogen source gas (NH ₃ gas) partial pressure is preferably 5 × 10 ³ Pa to 5 × 10 ⁴ Pa, and crystal growth temperature is preferably 900 ° C. to 1200 ° C.

  In the present embodiment, in the growth of the GaN crystal 20, the first crystal region 21 grows so as to embed the second crystal region. For this reason, as the GaN crystal 20 grows, the size of the second crystal region 22 that is the polarity reversal crystal region on the crystal growth surfaces 20a, 20b, and 20g decreases. In the present application, since the shape of the second crystal region on the crystal growth surface is indefinite, the size is defined by the square root of the area.

At this time, referring to FIG. 2B, the square root of the area of one second crystal region 22 on the crystal growth surface 20a when the crystal growth thickness T ₁ mm of the GaN crystal 20 is R ₁ μm, GaN When the square root of the area of the second crystal region 22 on the crystal growth surface 20b when the crystal growth height T ₂ mm of the crystal 20 is R ₂ μm, the amount of increase in the growth thickness of the GaN crystal 20 ( The ratio (R ₁ -R ₂ ) / (T ₂ -T ₁ ) of the reduction amount (R ₁ -R ₂ ) μm of the square root of the area of the one second crystal region 22 to T ₂ -T ₁ ) mm is It is preferably 10 μm / mm or more. By setting (R ₁ −R ₂ ) / (T ₂ −T ₁ ) to 10 μm / mm or more, it is possible to efficiently reduce and eliminate the size of the second crystal region 22 appearing on the crystal growth surface 20g of the GaN crystal 20. Can be done well.

Here, in order to set (R ₁ -R ₂ ) / (T ₂ -T ₁ ) to 10 μm / mm or more, in the HVPE method, the gallium source gas (GaCl gas) partial pressure is 1 × 10 ³ Pa to 5 × 10 ³ Pa, a nitrogen source gas (NH ₃ gas) partial pressure of ^{1 × 10 4 Pa~5 × 10 4} Pa, the crystal growth temperature is more preferable to be 1000 ° C. C. to 1100 ° C..

(Embodiment 2)
Another embodiment of the GaN crystal growth method according to the present invention is described with reference to FIGS. 3 and 4 in Embodiment 1, after the step of preparing the GaN substrate 10, the (0001) Ga main layer of the GaN substrate 10. The method further includes the step of forming a recess 12v in the polarity reversal crystal region 12 in the surface 10g, and the step of growing a GaN crystal on the (0001) Ga surface where the recess 11m is formed.

  In the GaN crystal growth method of the present embodiment, since the concave portion 12v is formed in the polarity reversal crystal region 12 in the (0001) Ga main surface 10g of the GaN substrate 10, the side surface of the main crystal region 11 forming the convex portion 11m. Since the first crystal region 21 of the GaN crystal 20 also grows in the portion, the square root of the area of the second crystal region on the crystal growth surface becomes small even when the recess 12v is filled with the GaN crystal 20.

Here, referring to FIG. 4A, the (0001) Ga surface 10g after the formation of the concave portion has a concave surface 10q and a convex surface 10p. 4B, the square root of the area of one second crystal region 22 of the GaN crystal 20 in the concave surface 10q of the GaN substrate 10 (this is equal to the area of the polarity reversal crystal region 12). Is R _S μm, and R _O is the square root of the area of the second crystal region 22 in the crystal growth surface 20z of the GaN crystal 20 in the same plane as the convex surface 10p of the GaN substrate 10, the recess 12v The ratio (R _S -R _O ) / D of the square root reduction amount (R _S -R _O ) μm of the area of the one second crystal region 22 to the depth D μm should be increased to 0.333 μm / μm or more. The size of the second crystal region 22 can be reduced more efficiently than when the crystal is grown thick.

Here, in order to increase the ratio (R _S −R _O ) / D to 0.333 μm / μm or more, in the HVPE method, the partial pressure of gallium source gas (GaCl gas) is 1 × 10 ³ Pa to 5 × 10 6. ³ Pa, a nitrogen source gas (NH ₃ gas) partial pressure of ^{1 × 10 4 Pa~5 × 10 4} Pa, the crystal growth temperature is more preferably set to 1000 ° C. C. to 1100 ° C..

In the GaN crystal growth method of this embodiment, the amount of reduction in the square root (R _S −R _O ) μm of the area of one second crystal region 22 due to the recess 12v is preferably 10 μm or more. The size of the second crystal region 22 appearing on the crystal growth surface 20g of the GaN crystal 20 is reduced by reducing the square root of the area of one second crystal region on the crystal growth surface by 10 μm or more when the recess is filled with the GaN crystal. It is possible to efficiently reduce and eliminate the thickness.

In the GaN crystal growth method of this embodiment, the depth _D μm of the concave surface 10q from the convex surface 10p is preferably three times or more the square root R _S μm of the area of the polarity inversion crystal region. The depth _D μm of the recess 12v is set to be not less than 3 times the square root R _S μm of the area of the polarity inversion crystal region 12, so that when the recess 12v of the GaN substrate 10 is filled with the GaN crystal 20, the crystal growth of the GaN crystal 20 occurs. The second crystal region 22 in the plane can be eliminated.

  The method for forming the recess 12v in the polarity-inverted crystal region 12 in the (0001) Ga main surface 10g of the GaN substrate 10 is not particularly limited, but from the viewpoint of easy formation of the recess, etching with acid or alkali is preferable. It is done. On the (0001) Ga main surface 10g of the GaN substrate 10, the (0001) Ga surface 11g of the main crystal region 11 and the (000-1) N surface 12n of the polarity reversal region 12 appear. -1) Since the N plane is more easily etched than the (0001) Ga plane, the polarity inversion region 12 in which the (000-1) N plane appears is selectively etched. Here, phosphoric acid, potassium hydroxide, sodium hydroxide or the like is preferably used as the etching agent. The (000-1) N main surface 10n of the (000-1) N main surface 10n of the GaN substrate is easily etched because the (000-1) N surface 11n appears in the main crystal region 11 on the (000-1) N main surface 10n. It is preferable to protect the (000-1) N main surface 10n with a platinum plate or the like so that the etching agent does not come into contact with the surface.

In the growth method of the present embodiment, as in the first embodiment, the growth thickness of the GaN crystal is increased in the step of growing the GaN crystal on the (0001) Ga main surface in which the concave portion of the GaN substrate is formed. The ratio (R ₁ -R ₂ ) / (T ₂ -T ₁ ) of the reduction amount (R ₁ -R ₂ ) μm of the square root of the area of one second crystal region to the amount (T ₂ -T ₁ ) mm is It is preferably 10 μm / mm or more.

(Embodiment 3)
One embodiment of the GaN crystal substrate according to the present invention is obtained by processing the GaN crystal 20 grown by the growth method of the first or second embodiment. Here, the processing of the GaN crystal means that a main surface obtained by cutting the GaN crystal 20 is polished to form a GaN crystal substrate. For example, in the GaN crystal substrate of the present embodiment, the GaN crystal 20 grown on the (0001) Ga surface 10g of the GaN substrate 10 is (0001) with reference to FIG. ) It is obtained by cutting a plurality of surfaces parallel to the Ga surface 10g and polishing the main surface.

  The GaN crystal substrates 201, 202, 203, 0204, 205, 206, 207, 208, and 209 of the present embodiment obtained in this way are referred to in FIG. The more the crystal growth thickness from the GaN substrate is, the smaller the polarity reversal region 22 is, the more the polarity inversion region 22 is reduced.

Example 1
First, with respect to a GaN substrate having a diameter of 2 inches (5.08 cm) and a thickness of 400 μm, the (0001) Ga main surface is etched with a 2N KOH aqueous solution at 50 ° C. for 30 minutes to obtain (0001) Ga of the GaN substrate 10. The number, density, and size (square root of area) of the polarity reversal crystal region on the main surface 10g were determined. On the (0001) Ga plane, there are 352 polarity reversal crystal regions, and there are 53 cases where the square root of the area exceeds 100 μm and 4 cases where the square root of the area exceeds 200 μm, and the square root of the area of the maximum polarity reversal crystal region Was 280 μm. Here, the area of each polarity inversion crystal region 12 was measured with an optical microscope.

  Next, referring to FIG. 4A, the polarity-reversed crystal region of this GaN substrate 10 was etched using a mixed melt of KOH and NaOH having a mass ratio of 1: 1. Etching conditions were set at a liquid temperature of 300 ° C. for 30 minutes. In etching, a platinum plate was brought into close contact with the (000-1) N main surface of the GaN substrate to prevent this surface from being etched.

  Etching using the above mixed melt formed 352 hexagonal columnar recesses having a square root of 20 μm to 100 μm on the (0001) Ga main surface of the GaN substrate. The depth of the recess was 50 μm to 250 μm. In addition, the variation in the depth of the concave portion is caused by the fact that the concave portion formed in the polarity reversal crystal region having a small square root of the area has a reduced depth because the etching solution is difficult to reach deep inside. is there.

Next, referring to FIGS. 4B and 4C, a GaN crystal 20 having a thickness of 10 mm is formed on the (0001) Ga main surface 10g in which the hexagonal columnar recesses of the GaN substrate 10 are formed by the HVPE method. Grown up. GaCl gas (gallium source gas) and NH ₃ gas (nitrogen source gas) generated by reacting the Ga melt and HCl gas at 800 ° C. were supplied to grow a GaN crystal on the GaN substrate at 1000 ° C. . Here, the GaCl gas partial pressure was 2 × 10 ³ Pa and the NH ₃ gas partial pressure was 2 × 10 ⁴ Pa.

  Next, referring to FIG. 4C, the GaN crystal 20 having a thickness of 10 mm is cut by a plurality of surfaces parallel to the (0001) Ga main surface 10g of the GaN substrate 10, and these main surfaces are polished. As a result, ten GaN crystal substrates 201, 202, 203, 204, 205, 206, 207, 208, 209, and 210 having a thickness of 500 μm were obtained. Here, the (0001) Ga main surface of the nth GaN crystal substrate counted from the GaN substrate side is at a distance of (1 × n) mm from the (0001) Ga main surface of the GaN substrate.

  The number and density of the second crystal regions (polarity inversion crystal regions) on the (0001) Ga main surface of each GaN crystal substrate obtained, and the square root of the area of the maximum second crystal region (maximum polarity inversion crystal region). Are summarized in Table 1.

  As is apparent from Table 1, the GaN crystal substrate obtained in the present example has a second crystal region (polarity inversion) as the GaN crystal substrate obtained from the position where the crystal growth thickness from the GaN substrate is large. The density and size of the crystalline region) were reduced.

  In this example, the square root of the area of the second crystal region on the crystal growth surface of the GaN crystal is reduced by 80 μm due to the recess formed in the GaN substrate, and further, with respect to the growth thickness of 1 mm of the GaN crystal. It decreased by 20 μm and decreased by a total of 100 μm. Therefore, the polarity reversal crystal region having a square root of the area of 100 μm or more on the (0001) Ga surface of the GaN substrate is the second crystal region (polarity reversal crystal region) on the (0001) Ga surface of the first GaN crystal substrate 201. Will remain. This is because the number of polarity reversal crystal regions (53) whose square root of the area existing on the (0001) Ga main surface of the GaN substrate is 100 μm or more and the (0001) Ga surface of the first GaN crystal substrate. This coincides with the fact that the number (51) of the second crystal regions to be substantially matched.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a schematic plan view showing an embodiment of a GaN substrate used in a GaN crystal growth method according to the present invention. It is a schematic sectional drawing which shows one Embodiment of the growth method of the GaN crystal concerning this invention. Here, (a) shows a GaN substrate, (b) shows a step of growing a GaN crystal on the GaN substrate, and (c) shows a step of manufacturing the GaN crystal substrate from the GaN crystal. It is a schematic plan view which shows other embodiment of the GaN board | substrate used in the GaN crystal growth method concerning this invention. It is a schematic sectional drawing which shows other embodiment of the growth method of the GaN crystal concerning this invention. Here, (a) shows the step of forming a recess in the polarity reversal crystal region of the GaN substrate, (b) shows the step of growing the GaN crystal on the GaN substrate, and (c) shows the step of growing the GaN crystal from the GaN crystal. The process of manufacturing is shown.

Explanation of symbols

  10 GaN substrate, 10g, 11g (0001) Ga main surface, 10n, 11n (000-1) N main surface, 10p convex surface, 10q concave surface, 11 main crystal region, 12 polarity inversion crystal region, 12g (000- 1) Ga plane, 12n (0001) N plane, 20 GaN crystal, 20a, 20b, 20g, 20z Crystal growth plane, 21 First crystal region, 22 Second crystal region, 201, 202, 203, 204, 205 , 206, 207, 208, 209, 210 GaN crystal substrate.

Claims (6)

Preparing a GaN substrate including a main crystal region and a plurality of polarity-inverted crystal regions in which the polarity in the [0001] direction is inverted with respect to the main crystal region;
A method for growing a GaN crystal comprising a step of growing a GaN crystal by a vapor phase method on a (0001) Ga main surface of the GaN substrate,
The GaN crystal includes a first crystal region that grows on the main crystal region, and a plurality of second crystal regions that grow on each of the polarity inversion regions,
The second crystal region has a polarity reversed in the [0001] direction with respect to the first crystal region,
The first crystal region has a crystal growth rate higher than that of the second crystal region, and grows so as to embed the second crystal region. When the crystal growth thickness of the GaN crystal is T ₁ mm, the square root of the area of one second crystal region on the crystal growth surface is R ₁ μm, and the crystal when the crystal growth height of the GaN crystal is T ₂ mm When the square root of the area of the one second crystal region on the growth surface is R ₂ μm,
The ratio (R ₁ -R) of the reduction amount (R ₁ -R ₂ ) μm of the area of the one second crystal region to the increase amount (T ₂ -T ₁ ) mm of the growth thickness of the GaN crystal. _{2) / (T 2 -T 1} ) growth method of a GaN crystal according to claim 1, characterized in that 10 [mu] m / mm or more. After the step of preparing the GaN substrate, further comprising the step of forming a recess in the polarity reversal crystal region in the (0001) Ga main surface of the GaN substrate,
The method for growing a GaN crystal according to claim 1, comprising a step of growing the GaN crystal on the (0001) Ga surface in which the recess is formed. The (0001) Ga surface after forming the recess has a recess surface and a convex surface,
The square root of the area of one second crystal region of the GaN crystal on the concave surface of the GaN substrate is R _S μm, and the crystal growth surface of the GaN crystal is in the same plane as the convex surface of the GaN substrate. When the square root of the area of the one second crystal region is R _O μm,
The method for growing a GaN crystal according to claim 3, wherein a reduction amount (R _S −R _O ) μm of the square root of the area of the one second crystal region due to the recess is 10 μm or more. 5. The GaN crystal growth according to claim 4, wherein a depth _D μm of the concave surface from the convex surface is at least three times a square root R _S μm of the area of the one polarity reversal crystal region. Method.   A GaN crystal substrate obtained by processing a GaN crystal grown by any of the growth methods according to claim 1.

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