JP2008230868A - Method for growing gallium nitride crystal and gallium nitride crystal substrate - Google Patents

Abstract

A method for growing a GaN crystal having a flat crystal growth surface and a high crystal growth rate is provided.
The growth method of a gallium nitride crystal is a method of growing a gallium nitride crystal on a main surface of an aluminum nitride crystal by a hydride vapor phase growth method, and the main surface is made of an aluminum nitride crystal (0001). It is an Al surface, and the growth temperature of the gallium nitride crystal is higher than 1100 ° C. and lower than 1400 ° C.
[Selection] Figure 1

Description

  The present invention relates to a method for growing a gallium nitride crystal (hereinafter also referred to as a GaN crystal) used for a substrate of a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor. More particularly, the present invention relates to a method for growing a GaN crystal and a GaN crystal substrate, in which a GaN crystal with good crystallinity is obtained at a high crystal growth rate and a high yield.

  The GaN crystal is very useful as a material for forming semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. Methods for producing such GaN crystals include HVPE (Hydride Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, MOCVD (Metal Organic Chemical Vapor Deposition). Vapor phase growth methods such as phase deposition method have been proposed (for example, Akira Usui and three others, “Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy”, Jpn. J. Appl. Phys., Vol. 36, (1997), L899-L902 (hereinafter referred to as non-patent document 1)).

  In the above vapor phase growth method, a substrate for growing a GaN crystal is required. However, since the GaN crystal is expensive and difficult to obtain, the silicon carbide substrate (hereinafter referred to as the SiC substrate) is easily available and inexpensive. GaN crystal is grown on a heterogeneous substrate having a chemical composition different from that of GaN, such as a silicon substrate (hereinafter also referred to as a Si substrate), a sapphire substrate. Here, since the lattice constant and the linear expansion coefficient are different between the SiC substrate, the Si substrate or the sapphire substrate and the GaN crystal, it is amorphous on the SiC substrate, the Si substrate or the sapphire substrate in order to grow a highly crystalline GaN crystal. Forming a buffer layer of aluminum nitride (AlN) or gallium nitride (GaN), then raising the temperature to crystallize the buffer layer, and then growing a GaN crystal thereon (for example, H. Amano and three others, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer”, Appl. Phys. Lett., Vol. 48, No. 5, (1986), 353-355 ( Hereinafter, refer to Non-Patent Document 2)).

  However, in the crystal growth methods disclosed in Non-Patent Document 1 and Non-Patent Document 2, cracks are likely to occur as the thickness of the GaN crystal to be grown increases. In addition, since the buffer layer is not a complete single crystal, it is difficult to grow a GaN crystal with good crystallinity.

Here, the MBE method and the MOCVD method are disadvantageous for producing a thick GaN crystal because the crystal growth rate is low. The HVPE method is advantageous in that the crystal growth rate is higher than that of the MBE method and the MOCVD method, and a thick crystal can be easily produced. There was a problem that the yield of the obtained substrate was lowered.
Akira Usui, 3 others, “Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy”, Jpn. J. Appl. Phys., Vol. 36, (1997), L899-L902 H. Amano and three others, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer”, Appl. Phys. Lett., Vol. 48, No. 5, (1986), 353-355.

  In order to solve the above problems, an object of the present invention is to provide a method for growing a GaN crystal having a flat crystal growth surface and a high crystal growth rate.

  The present invention is a method for growing a gallium nitride crystal on a main surface of an aluminum nitride crystal by a hydride vapor phase growth method, the main surface being a (0001) Al surface of the aluminum nitride crystal, A growth method of a gallium nitride crystal characterized in that the growth temperature is higher than 1100 ° C. and lower than 1400 ° C.

  In the method for growing a gallium nitride crystal according to the present invention, the growth temperature of the gallium nitride crystal can be set to 1200 ° C. or higher and 1300 ° C. or lower. Aluminum nitride crystals can also be formed on a silicon carbide substrate. Moreover, the aluminum nitride crystal can be grown by a sublimation method. Further, the gallium nitride crystal can be grown to a thickness of 3 mm or more.

  The present invention is also a gallium nitride crystal substrate obtained by processing a gallium nitride crystal grown by the above growth method.

  According to the present invention, it is possible to provide a method for growing a GaN crystal having a flat crystal growth surface and a high crystal growth rate.

(Embodiment 1)
One embodiment of a method for growing a gallium nitride crystal (GaN crystal) according to the present invention is described with reference to FIG. 1 on a main surface of an aluminum nitride crystal (AlN crystal) 1 by a hydride vapor phase growth method. A method of growing (GaN crystal) 3, the main surface of which is the (0001) Al surface of aluminum nitride crystal (AlN crystal) 1, and the growth temperature of gallium nitride crystal (GaN crystal) 3 is higher than 1100 ° C. It is characterized by being lower than 1400 ° C.

  The AlN crystal has the same crystal structure as the GaN crystal and has a crystal constant close to that of the SiC crystal, Si crystal, or sapphire crystal. Therefore, if the AlN crystal has high crystallinity, a GaN crystal with high crystallinity can be directly grown on the main surface without forming a buffer layer.

  In the AlN crystal 1, the main surface on which the GaN crystal 3 is grown is not particularly limited. However, from the viewpoint of obtaining a large-diameter GaN crystal with a large main surface of the AlN crystal, it may be a (0001) surface. preferable. Here, the (0001) Al surface means a surface substantially parallel to the (0001) Al surface. For example, the (0001) Al surface includes an Al surface (referred to as a surface on which Al atoms appear) having an off angle of 5 ° or less formed by the surface and the (0001) plane. Such an off-angle can be measured by X-ray diffraction.

  Further, in the AlN crystal 1, there are cases where an Al atomic plane appears on the main surface and an N atomic plane appears. Here, a GaN crystal whose crystal growth surface is the Ga surface grows on the surface where the Al atoms appear (Al surface), and a GaN crystal whose crystal growth surface is the N surface on the surface where the N atoms appear (N surface). Will grow. Here, in the GaN crystal growth, the crystallinity is higher when the Ga surface is used as a crystal growth surface than in other cases. Therefore, even if the (0001) Al surface which is the main surface of the AlN crystal has a small off angle (for example, 5 ° or less) with respect to the (0001) plane, the GaN crystal has the Ga surface as the crystal growth surface. Since it grows, a highly crystalline GaN crystal is obtained.

  The GaN crystal is grown by the HVPE method. In the growth of a GaN crystal by the HVPE method, for example, an HVPE apparatus 10 as shown in FIG. 4 is used. The HVPE apparatus 10 includes a susceptor 13 for placing a SiC substrate 9 having an AlN crystal 1 formed on a main surface thereof in a reaction vessel 11 and a gallium source gas inlet for introducing a gallium source gas 6 onto the AlN crystal 1. 11a, a nitrogen source gas introduction port 11b for introducing the nitrogen source gas 7 onto the AlN crystal 1, an exhaust port 11c for exhausting the gas after the reaction, and a susceptor 13 for heating the AlN crystal 1 The heater 15 and the heater 17 for heating the reaction vessel 11 are disposed. The susceptor 13 can rotate the substrate placed thereon.

Referring to FIG. 4, using the HVPE apparatus 10, for example, a GaN crystal can be produced as follows. An SiC substrate 9 having an AlN crystal 1 formed on the main surface is disposed on a susceptor 13 installed in the reaction vessel 11, for example, GaCl gas is used as the gallium source gas 6, and NH ₃ gas is used as the nitrogen source gas 7. Is introduced into the reaction vessel 11, and the gallium source gas 6 and the nitrogen source gas 7 are reacted to grow the GaN crystal 3 on the AlN crystal 1. The partial pressure of the gallium source gas 6 is about 50 Pa to 1 × 10 ⁴ Pa, the partial pressure of the nitrogen source gas 7 is about 5 × 10 ³ Pa to 5 × 10 ⁴ Pa, and the gas of the gallium source gas 6 and the nitrogen source gas 7. The ratio (molar ratio) is about 1:10 to 1: 1000, and the growth temperature of the GaN crystal is usually 1000 ° C. to 1100 ° C. In the present embodiment, it is higher than 1100 ° C. and lower than 1400 ° C.

Here, when introducing the gallium source gas and the nitrogen source gas, a carrier gas such as H ₂ gas, N ₂ gas or Ar gas can be used. By adding the carrier gas to the gallium source gas or the nitrogen source gas, the introduction amount of the gallium source gas or the nitrogen source gas can be stabilized, and the reactivity between the gallium source gas and the nitrogen source gas can be adjusted, A GaN crystal with good crystallinity can be obtained efficiently.

  The HVPE method has a higher crystal growth rate than the MBE method and the MOCVD method, and can easily produce a thick crystal. However, referring to FIG. 1, when a GaN crystal is grown on the main surface of an AlN crystal at a crystal growth temperature of 1000 ° C. or higher and 1100 ° C. or lower, which is usually used in the HVPE method, a plurality of facets 3f are formed on the crystal growth surface 3g. The hexagonal pyramid-shaped recess 3p is easily formed, and the crystal growth surface 3g tends to be an uneven surface, so that the yield of the GaN crystal substrate 3s obtained from the grown GaN crystal 3 is lowered.

  In order to suppress the formation of the recess 3p, flatten the crystal growth surface 3g, and increase the yield of the substrate obtained from the grown GaN crystal, the growth temperature of the GaN crystal is set higher than 1100 ° C. from the GaN crystal. . In order to keep the crystal growth rate high, the growth temperature of the GaN crystal is set lower than 1400 ° C. From this viewpoint, the growth temperature of the GaN crystal needs to be higher than 1100 ° C. and lower than 1400 ° C., and is preferably 1200 ° C. or higher and 1300 ° C. or lower.

  When a GaN crystal is grown at a crystal growth temperature higher than 1100 ° C. and lower than 1400 ° C. using a GaN substrate as a base substrate, decomposition tends to occur from the (000-1) N plane side of the GaN substrate. In particular, when the temperature exceeds 1250 ° C., decomposition of the GaN substrate increases. For this reason, in the GaN substrate, it is difficult to grow GaN crystals in the temperature range of this embodiment, particularly in a high temperature of 1250 ° C. or higher.

  When a GaN or AlN buffer layer is formed on a SiC substrate, Si substrate, or sapphire substrate, and a GaN crystal is grown at a crystal growth temperature higher than 1100 ° C. and lower than 1400 ° C., the buffer of GaN or AlN is used. The decomposition of the layer is suppressed by the SiC substrate, the Si substrate, or the sapphire substrate, but the GaN crystal to be grown tends to crack. The occurrence of such cracks is considered to be due to stress generated when a large amount of dislocations due to the buffer layer occur on the crystal growth surface 3g and these dislocations are coalesced by growth.

  In the GaN crystal growth method of this embodiment, the AlN crystal for growing the GaN crystal may be a free-standing crystal substrate or a crystal layer formed on another substrate. Since a self-supporting AlN crystal substrate has better crystallinity and less warpage than an Al crystal layer formed on another substrate, a GaN crystal with good crystallinity can be grown. However, a self-supporting AlN crystal substrate is expensive and it is difficult to obtain a large-diameter substrate. In comparison with this, other substrates, for example, SiC substrates are inexpensive and it is easy to obtain a large-diameter substrate. From this point of view, referring to FIG. 1A, AlN crystal 1 is preferably formed on main surface 9 m of SiC substrate 9.

In the GaN crystal growth method of this embodiment, referring to FIG. 1A, the AlN crystal 1 is preferably grown by a sublimation method. Here, the sublimation method in the present embodiment refers to a method of obtaining an AlN crystal 1 by sublimating an AlN raw material 5 such as an AlN powder and then solidifying it again with reference to FIG. In the crystal growth by the sublimation method, for example, a high-frequency heating type vertical sublimation furnace 20 as shown in FIG. 5 is used. A silicon nitride (BN) crucible 23 having an exhaust port 23 c is provided at the center of the reaction vessel 21 in the vertical sublimation furnace 20, and air is passed around the crucible 23 from the inside of the crucible 23 to the outside. A heating element 25 is provided to ensure. In addition, a high-frequency heating coil 27 for heating the heating body 25 is provided in the outer central portion of the reaction vessel 21. Further, at the end of the reaction vessel 21, there are N ₂ gas introduction port 21 a and N ₂ gas exhaust port 21 c for allowing N ₂ gas to flow outside the crucible 23 of the reaction vessel 21, and the temperatures of the lower and upper surfaces of the crucible 23. A radiation thermometer 29 is provided for measuring.

Referring to FIG. 5, by using the vertical sublimation furnace 20, the AlN crystal 1 used in the present embodiment can be produced as follows, for example. The AlN raw material 5 such as AlN powder is stored in the lower part of the crucible 23, and the temperature in the crucible 23 is increased by heating the heating body 25 using the high-frequency heating coil 27 while flowing N ₂ gas into the reaction vessel 21. Then, by maintaining the temperature of the crucible 23 on the side of the AlN raw material 5 higher than the temperature of the other portions, AlN is sublimated from the AlN raw material 5, and the AlN is solidified again at the upper part of the crucible 23, and the AlN Crystal 1 is grown. Here, by disposing a base substrate (for example, SiC substrate 9) for growing an AlN crystal on the crucible 23, the AlN crystal 1 can be grown on the base substrate.

Here, during the growth of the AlN crystal 1, the temperature of the crucible 23 on the side of the AlN raw material 5 is about 1800 ° C. to 2200 ° C., and the temperature of the SiC substrate 9 on the upper side of the crucible 22 is 1 ° C. to By reducing the temperature to about 100 ° C., the AlN crystal 1 having good crystallinity that cannot be obtained by other growth methods can be obtained even when growing on a different substrate such as a SiC substrate. Further, during the crystal growth, N ₂ gas is continuously supplied to the outside of the crucible 22 in the reaction vessel 21 so that the gas partial pressure is about 101.3 hPa to 1013 hPa, thereby reducing the contamination of impurities into the AlN crystal 1. can do.

  During the temperature rise inside the crucible 23, impurities inside the crucible 23 can be removed through the exhaust port 23 c by raising the temperature of the other portion than the temperature on the AlN raw material 5 side of the crucible 23. Impurity contamination into the AlN crystal 1 can be reduced.

By the sublimation method, the AlN crystal 1 having good crystallinity with a dislocation density of 1 × 10 ⁶ cm ⁻² or less is obtained. Note that the dislocation density of the AlN crystal 1 can be reduced to about 1 × 10 ³ cm ⁻² to 1 × 10 ⁵ cm ⁻² by optimizing the conditions of the sublimation method.

  As described above, according to the sublimation method, an AlN crystal having good crystallinity can be obtained regardless of the presence or absence of the base substrate. From the viewpoint of obtaining a large-diameter AlN crystal, it is preferable to grow the AlN crystal on the base substrate. As the base substrate, a SiC substrate is preferable from the viewpoint of having a lattice constant close to that of the GaN crystal to be grown and not being decomposed even in an AlN sublimation growth atmosphere.

  In the GaN crystal growth method of this embodiment, referring to FIG. 1B, the GaN crystal is preferably grown so that its thickness T is 3 mm or more. By setting the thickness T of the GaN crystal to 3 mm or more, cracks are generated in the GaN crystal due to the thermal stress generated during cooling after the growth of the GaN crystal due to the difference in thermal expansion coefficient between GaN and AlN. A GaN crystal can be peeled from an AlN crystal (for example, an AlN crystal layer formed on a free-standing AlN crystal substrate or a Si substrate) without being generated.

(Embodiment 2)
A gallium nitride crystal substrate (hereinafter also referred to as a GaN crystal substrate) according to the present invention is obtained by processing a gallium nitride crystal (GaN crystal) 3 grown by the growth method of Embodiment 1 with reference to FIG. The GaN crystal substrate 3s obtained in this way.

  Since the GaN crystal substrate of the present embodiment is obtained by processing the GaN crystal grown by the growth method of Embodiment 1, a GaN crystal substrate having high crystallinity can be obtained efficiently and with a high yield.

  Here, the method for processing the GaN crystal 3 is not particularly limited. For example, referring to FIG. 1C, the GaN crystal substrate 3 s is obtained by cutting the GaN crystal 3. The cut surface is not particularly limited, but is preferably a surface parallel to the main surface 1 m of the AlN crystal 1 from the viewpoint of obtaining a large-diameter substrate. The GaN crystal substrate 3s is preferably mirror-finished by polishing or etching from the viewpoint of forming a semiconductor layer with good crystallinity on the main surface 3sm. The polishing method is not particularly limited, and a mechanical polishing method or a chemical mechanical polishing method (CMP) is preferably used. The etching method is not particularly limited, and vapor phase etching and liquid phase etching are preferably used.

1. Preparation of AlN Crystal Referring to FIGS. 1 (a) and 2, a 6H—SiC substrate 9 having a diameter of 4 inches (101.6 mm) and a thickness of 0.5 mm (with a main surface 9m of (0001) Si surface) An AlN crystal layer (AlN crystal 1) having a thickness of 5 to 10 μm was grown on the substrate (having an off angle of 4 °) by a sublimation method. The plane orientation of the main surface of the grown AlN crystal layer (AlN crystal 1) is a (0001) Al plane as measured by X-ray diffraction, that is, the main plane of the AlN crystal 1 and the (0001) plane. The off angle was 4 °. 1A corresponds to a cross-sectional view taken along the line IA in FIG. The growth temperature of the AlN crystal 1 was 1850 ° C. when the temperature on the back surface (000-1) C surface side of the SiC substrate was measured with a radiation thermometer. Referring to FIGS. 1A and 2, the AlN crystal layer (AlN crystal 1) was grown almost uniformly and flatly on the SiC substrate 9, but when observed with an optical microscope, the average diameter was 100. An irregular pit 1p of about 200 μm (referring to a portion where the AlN crystal 1 is not grown, hereinafter the same) was present at a density of 20 cm ⁻² . Here, this AlN crystal layer (AlN crystal 1) has a high crystallinity of the half width of the X-ray diffraction peak for the (0004) plane of 30 arcsec, and has an average dislocation density measured by etching with molten KOH / NaOH. It was as low as 1 × 10 ⁶ cm ⁻² . Note that the pits 1p of the AlN crystal layer (AlN crystal 1) may disappear as the thickness of the AlN crystal layer increases.

2. Growth of GaN crystal Referring to FIG. 1B, a GaN crystal 3 was grown by HVPE on the AlN crystal layer (AlN crystal 1) having a low dislocation density and high crystallinity obtained by the sublimation method. .

Specifically, referring to FIG. 4, SiC substrate 9 on which AlN crystal 1 is formed on main surface 9 m is placed on susceptor 13 in reaction vessel 11, and GaCl gas (gallium) is placed in reaction vessel 11. Source gas 6) and NH ₃ gas (nitrogen source gas 8) were introduced. H ₂ gas was used as a carrier gas for GaCl gas and NH ₃ gas. Here, the partial pressure of GaCl gas is 2 × 10 ³ Pa, the partial pressure of NH ₃ gas is 2 × 10 ⁴ Pa, and the total flow rate of GaCl gas, NH ₃ gas and H ₂ gas is 20 SLM (SLM is This is an abbreviation for standard liter per minute, which is a unit expressed in liters per minute in a standard state (1013 hPa, 0 ° C.)

  Since the growth temperature of the GaN crystal cannot measure the temperature of the AlN crystal during the growth of the GaN crystal, a ceramic substrate (for example, an AlN ceramic substrate) incorporating a thermocouple is disposed on the susceptor 13 (not shown). 1) The temperature of the ceramic substrate when the HVPE apparatus 10 was operated under the set conditions in accordance with the growth conditions of the GaN crystal. Actually, the conditions of the HVPE apparatus 10 were set so that the temperature of the ceramic substrate became a predetermined temperature, and the GaN crystal was grown under these conditions. Here, the growth temperature of the GaN crystal is 1050 ° C. (Comparative Example 1), 1100 ° C. (Comparative Example 2), 1150 ° C. (Example 1), 1200 ° C. (Example 2), 1250 ° C. (Example 3), GaN crystals were grown at 1300 ° C. (Example 4), 1350 ° C. (Example 5), 1400 ° C. (Comparative Example 3), and 1450 ° C. (Comparative Example 4), respectively. The growth time of the GaN crystal was 50 hours in all cases. The growth rates of the GaN crystals at this time are 510 μm / hr (Comparative Example 1), 460 μm / hr (Comparative Example 2), 350 μm / hr (Example 1), 330 μm / hr (Example 2), and 310 μm, respectively. / Hr (Example 3), 240 μm / hr (Example 4), 50 μm / hr (Example 5), and 15 μm / hr (Comparative Example 3). In the case of Comparative Example 4, the GaN crystal was not grown. The results are summarized in Table 1.

3. Evaluation of GaN Crystal When the GaN crystal was grown in a temperature range of 1050 ° C. to 1300 ° C., a GaN crystal having a diameter of 4 inches (101.6 mm) with no occurrence of cracks was obtained (Comparative Example 1). , 2, Examples 1-4). Further, when these crystals were taken out from the HVPE apparatus, the AlN crystal and the SiC substrate were cracked and separated from the GaN crystal. When a GaN crystal was grown at 1350 ° C., the GaN crystal, AlN crystal, and SiC-based substrate were all cracked (Example 5). Further, when the GaN crystal was grown at 1400 ° C., the GaN crystal was cracked and peeled off from the SiC substrate on which the AlN crystal was formed (Comparative Example 3). The results are summarized in Table 1.

  Referring to FIGS. 1B and 3, a (0001) Ga face 3 c appeared on the crystal growth surface 3 g of the obtained GaN crystal 3. The appearance of the (0001) Ga surface 3c in the crystal growth surface 3g was confirmed by X-ray diffraction of the GaN crystal. Further, when the crystal growth temperature was low, the crystal growth surface 3g was formed with a recess 3p composed of a plurality of facets 3f, and the crystal growth surface 3g was an uneven surface. The flatness of the crystal growth surface 3g was evaluated by the (0001) Ga plane occupancy (%) defined below. As defined below, the higher the (0001) Ga plane occupancy, the flatter the crystal growth surface, and the lower the (0001) Ga plane occupancy, the greater the crystal growth surface unevenness. 1B corresponds to a cross-sectional view taken along the line IB in FIG.

The (0001) Ga plane occupancy (%) is the area of the (0001) Ga plane relative to the total area S of the crystal growth plane 3g of the GaN crystal 3 when the thickness T from the main plane 1m of the AlN crystal is grown to 10 mm. It is defined as the percentage of Sc and the following formula (1)
(0001) Ga plane occupancy (%) = 100 × Sc / S (1)
It is represented by However, when the crystal growth temperatures were 1350 ° C. and 1400 ° C., the GaN crystal was not grown to a thickness of up to 10 mm, so the (0001) Ga plane occupation ratio of the crystal growth surface at the thickness after the crystal growth was used. S is the sum of the area Sp of the recess 3p on the crystal growth surface 3g and the Sc.

  Here, the (0001) Ga plane occupancy (%) was measured by observing the crystal growth surface of the GaN crystal grown to a predetermined thickness with a fluorescence microscope. According to the fluorescence microscope, it is possible to discriminate between the (0001) Ga surface 3c portion and the recessed portion 3p portion based on the difference in fluorescence intensity.

  In this example, a GaN crystal was grown on an AlN crystal where pits 1p were present. However, even when a GaN crystal was grown on an AlN crystal where pits 1p were not present, (0001 ) It has been confirmed that a Ga surface 3c portion and a recess 3p are formed.

  The relationship between the growth temperature of the GaN crystal and the (0001) Ga plane occupancy is 12% at 1050 ° C. (Comparative Example 1), 75% at 1100 ° C. (Comparative Example 2), and 91% at 1150 ° C. Example 1) 97% at 1200 ° C. (Example 2) and 100% (Examples 3 to 5 and Comparative Example 3) within the range of 1250 ° C. to 1400 ° C. The results are summarized in Table 1.

  Further, the relationship between the growth temperature of the GaN crystal and the half width of the X-ray diffraction peak for the (0004) plane is 150 arcsec (Comparative Example 1) at 1050 ° C. and 90 arcsec (Comparative Example 2) at 1100 ° C., respectively. 40 arcsec at 1150 ° C. (Example 1) 30 arcsec at 1200 ° C. (Example 2) 20 arcsec at 1250 ° C. (Example 3) 20 arcsec at 1300 ° C. (Example 4) 40 arcsec at 1350 ° C. Example 5) It was 70 arcsec (Comparative Example 3) at 1400 ° C. The results are summarized in Table 1.

  Referring to Table 1, the (0001) Ga plane occupancy is low when the crystal growth temperature is as low as 1050 ° C. and 1100 ° C. (Comparative Examples 1 and 2), but is 91% when the crystal growth temperature is 1150 ° C. (Example 1), the crystal growth temperature was improved to 97% at 1200 ° C. (Example 2), and the crystal growth temperature was 100% within the range of 1250 ° C. to 1400 ° C. (Examples 3 to 5, Comparative Example 3).

  As for the crystal growth rate, the crystal growth temperature is decreased from 1050 ° C. to 1200 ° C. (Comparative Examples 1, 2, and Examples 1 and 2). This is because the crystal growth surface shifts from an uneven surface to a flat surface. This is considered to be a decrease in the apparent growth rate. When the crystal growth temperature is 1200 ° C. to 1300 ° C., the rate of decrease in the crystal growth rate is small (Examples 2 to 4). When the crystal growth temperature was higher than 1300 ° C., the crystal growth rate rapidly decreased (Example 5, Comparative Example 3), and no GaN crystal was grown at a crystal growth temperature of 1450 ° C. (Comparative Example 4).

  Therefore, by growing a GaN crystal on an AlN crystal by an HVPE method at a crystal growth temperature higher than 1100 ° C. and lower than 1400 ° C., preferably at a crystal growth temperature not lower than 1200 ° C. and not higher than 1300 ° C. It was found that a GaN crystal having a high crystal growth rate and high flatness of the crystal growth surface can be grown.

  Further, it is understood that a GaN crystal grown at a crystal growth temperature higher than 1100 ° C. and lower than 1400 ° C. has an excellent crystallinity with a half-value width of the X-ray diffraction peak for the (0004) plane of 20 arcsec to 40 arcsec. It was.

  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.

It is a schematic sectional drawing which shows one Embodiment of the method of growing a GaN crystal on an AlN crystal. Here, (a) is a schematic cross-sectional view showing an AlN crystal, (b) is a schematic cross-sectional view showing how a GaN crystal is grown, and (c) is a schematic cross-sectional view showing how a GaN crystal is processed. It is. It is a schematic plan view which shows an AlN crystal. It is a schematic plan view which shows the grown GaN crystal. In this invention, it is a schematic sectional drawing which shows the HVPE apparatus for growing a GaN crystal. In this invention, it is a schematic sectional drawing which shows the sublimation furnace for growing an AlN crystal | crystallization.

Explanation of symbols

1 AlN crystal, 1 m, 3 sm, 9 m main surface, 1p pit, 3 GaN crystal, 3c (0001) Ga surface, 3f facet, 3g crystal growth surface, 3p recess, 3s GaN crystal substrate, 5 AlN source, 6 gallium source gas 7 Nitrogen source gas, 9 SiC substrate, 10 HVPE apparatus, 11, 21 reaction vessel, 11a Gallium source gas inlet, 11b Nitrogen source gas inlet, 11c, 23c Exhaust port, 13 Susceptor, 15, 17 Heater, 20 Sublimation Furnace, 21a N ₂ gas inlet, 21c N ₂ gas outlet, 23 crucible, 25 heating element, 27 high frequency heating coil, 29 radiation thermometer.

Claims (6)

A method of growing a gallium nitride crystal on a main surface of an aluminum nitride crystal by a hydride vapor phase growth method,
The main surface is a (0001) Al surface of the aluminum nitride crystal;
A method for growing a gallium nitride crystal, wherein the growth temperature of the gallium nitride crystal is higher than 1100 ° C. and lower than 1400 ° C.   2. The method for growing a gallium nitride crystal according to claim 1, wherein a growth temperature of the gallium nitride crystal is 1200 ° C. or higher and 1300 ° C. or lower.   The gallium nitride crystal growth method according to claim 1 or 2, wherein the aluminum nitride crystal is formed on a silicon carbide substrate.   The gallium nitride crystal growth method according to any one of claims 1 to 3, wherein the aluminum nitride crystal is grown by a sublimation method.   The gallium nitride crystal growth method according to any one of claims 1 to 4, wherein the gallium nitride crystal is grown to a thickness of 3 mm or more.   A gallium nitride crystal substrate obtained by processing a gallium nitride crystal grown by any of the growth methods according to claim 1.

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