METHOD FOR MANUFACTURING GaN SINGLE CRYSTAL SUBSTRATE AND GaN SINGLE CRYSTAL SUBSTRATE

The present invention relates to a method for manufacturing a gallium nitride (GaN) single crystal substrate used as a substrate for a light emitting diode made of a group 3-5 compound semiconductor or a light emitting device such as a semiconductor laser.

Light emitting devices using nitride semiconductors have already been put into practical use, including blue LEDs. Conventionally, sapphire has been used as a substrate almost without exception in light emitting devices using nitride semiconductors. A gallium nitride crystal thin film grows well on the sapphire substrate. The sapphire substrate is robust and has sufficient mechanical strength. The gallium nitride thin film grown on the sapphire substrate has many defects, but nevertheless emits light. Defects do not grow and deteriorate. Sapphire is an excellent substrate material for the growth of nitride semiconductor thin films.

However, there are still problems with sapphire substrates. Sapphire is not cleavable. Sapphire is an insulator. There is a large mismatch with gallium nitride due to lattice mismatch. Nitride-based semiconductor light emitting devices using a sapphire substrate have such a problem. In the case of a light emitting diode, the yield does not increase because there is no cleavage in the dicing process, resulting in high cost. In the case of a semiconductor laser, a good resonator reflecting surface could not be produced by cleavage, and there was a problem in terms of quality such as laser characteristics.

Since sapphire is an insulator, electrodes cannot be provided on the upper and lower surfaces of the device chip as in ordinary LEDs. An n-type GaN layer for n-electrodes is attached on a sapphire substrate, and after epi-growth of a GaN layer, InGaN layer, etc. on it, the ends are etched to the n-type GaN layer to expose the n-type GaN layer. And an n electrode was formed on it. It increases the number of processes and the process time, resulting in high cost.

Furthermore, since it is necessary to provide two electrodes side by side on the same surface (surface side), a large chip area is required. That also pushes up costs. Since the lattice constants of sapphire and gallium nitride are quite different, there is also a problem that defects such as many dislocations are introduced into the epi layer due to the mismatch of the lattice constant between the substrate and the epi layer.

In fact, 1 × 10 is included in the gallium nitride epi layer of a light emitting device using a sapphire substrate currently on the market.⁹cm^-2There are some degree of high density dislocations. Even when a SiC substrate with less lattice mismatch than sapphire is used and gallium nitride is grown on it, the dislocation density is about that level, and there is not much improvement.

The existence of such high-density dislocations has not been a major obstacle in practical use for LEDs. Defects do not increase or multiply due to dislocations. However, since the semiconductor laser has a high current density, it is considered that these defects are the causes that hinder the extension of the life of the semiconductor laser. That is, in the case of a semiconductor laser, a substrate having a smaller mismatch is desired. As the output of LEDs increases, it is considered that an epi layer with lower dislocations will be required as a substrate for LEDs.

<patcit num="1"><text>Special application Hei 9-298300</text></patcit><patcit num="2"><text>Japanese Patent Application No. 10-9008</text></patcit><patcit num="3"><text>Japanese Patent Application No. 10-102546</text></patcit><patcit num="4"><text>Japanese Patent Application Laid-Open No. 2-239188</text></patcit><patcit num="5"><text>Japanese Patent Application Laid-Open No. 64-32686</text></patcit><patcit num="6"><text>Japanese Patent Application Laid-Open No. 64-22072</text></patcit><patcit num="7"><text>Japanese Patent Application Laid-Open No. 64-15914</text></patcit><patcit num="8"><text>Japanese Patent Application Laid-Open No. 1-270599</text></patcit><patcit num="9"><text>Patent No. 3129112</text></patcit><patcit num="10"><text>Japanese Patent Application Laid-Open No. 7-201745</text></patcit><patcit num="11"><text>Japanese Patent Application Laid-Open No. 11-74562</text></patcit>

<nplcit num="1"><text>Takayuki Yuasa, Yoshihiro Ueta, Yuzoh Tsuda, Atushi Ogawa, Mototaka Taneya and Katsutoshi Takao, Effect of Slight Misorientation of Sapphire Substrate on Metalorganic Chemical Vapor Deposition Growth of GaN, Jpn.J.Appl.Phys.vol.38 (1999), pp.L703-L705, Part2, No.7A, 1 July 1999</text></nplcit><nplcit num="2"><text>MHXie, LXZheng, SHCheung, YFNg, Huasheng Wu, SYTong, and N.Ohtani, Reduction of threading defects in GaN grown on vicinal SiC (0001) by molecular-beamepitaxy, Applied Physics Letters Vol.77, No.8, p1105 -1107, 21 August 2000</text></nplcit>

The most ideal substrate on which a nitride-based semiconductor thin film should grow is considered to be a gallium nitride (GaN) crystal substrate. If a high-quality gallium nitride crystal substrate is obtained, the problem of lattice constant mismatch between the substrate and the thin film can be solved. The gallium nitride crystal has a clear cleavage property, and a natural cleavage plane can be used as a reflector of a laser resonator. Furthermore, since gallium nitride is a semiconductor rather than an insulator like sapphire, electrodes can be attached to the bottom surface of the substrate, and the chip area can be reduced. As such, the gallium nitride crystal substrate seems to be most suitable as a substrate for growing a nitride-based semiconductor thin film.

However, nevertheless, the sapphire substrate is still used almost exclusively as the substrate. This is partly because it is difficult to manufacture a gallium nitride self-supporting crystal substrate with high quality and practical size. GaN can be melted at ultra-high pressure and ultra-high temperature, and crystals can grow from the melt, but it can only produce small crystal grains, and it is still not possible to produce large-diameter ones.

Since it is difficult to melt GaN, gallium nitride crystals are produced by a vapor phase growth method in which a gas raw material is reacted in a gas phase. The method originally used for thin film growth, which is to grow a gallium nitride thin film by vapor phase synthesis on a dissimilar crystal substrate, is diverted to the substrate growth method.

As a vapor phase growth method for a GaN thin film, an HVPE method, a sublimation method, a MOC method, a MOCVD method, and the like are known. (1) In the HVPE method (Hydride Vapor Phase Epitaxy), a container containing Ga metal is provided above the hot wall type reactor, a susceptor is provided below, and a base substrate is placed on the susceptor to cover the entire reactor. Heat and blow HCl gas diluted with hydrogen from above into the Ga container to 2Ga + 2HCl 2GaCl + H.₂Gas of GaCl was synthesized by the reaction of, and when it descended near the susceptor, it was diluted with hydrogen.₃Blow in gas 2GaCl + 2NH₃ 2GaN + 3H₂A GaN crystal is laminated on a base substrate that has been heated by causing the above reaction.

(2) In the sublimation method, the base substrate is fixed downward on the reactor, and a GaN polycrystal is placed under the reactor to form a temperature gradient in the reactor such that the lower part is hotter and the upper part is colder. As a result, the polycrystal vaporizes and rises, and gradually accumulates on the underlying substrate to form a single crystal thin film.

(3) In the MOCVD (Metal-organic Chemical Vapor Deposition) method, a susceptor is provided below the cold wall type reactor, a base substrate is placed on it, the susceptor is heated, and hydrogen gas is blown from above. Carrier gases include trimethylgallium (TMG), triethylgallium (TEG) and NH₃Blow in gas (CH₃) 3Ga + NH₃ GaN + 3CH₄A vapor phase reaction is caused to deposit GaN crystals on the underlying substrate. Currently, it is the most commonly used method for growing a nitride semiconductor thin film on a sapphire substrate. It has this name because it is made from organic metals. However, this is a carbon-containing material that NH₃The applicant thinks that this is not a very good method because carbon is mixed with GaN and the carbon causes a yellow color or a deep donor level.

(4) The MOC (Metall organic Chloride) method uses an organic metal as a raw material for Ga, but it is directly NH.₃After reacting with HCl and synthesizing GaCl as an intermediate product without reacting with₃To make GaN. The MOC method is unique to the applicant and is unique. The advantage over the MOCVD method is that since GaCl is formed as an intermediate product, carbon is less likely to be mixed into the final product GaN.

Sapphire (Al) is used as the base substrate.₂O₃) Is the most. Sapphire has a large difference in lattice constant from GaN and has a high dislocation density of thin films, but it can still be used as an LED and has a long life. However, there are reports that GaAs, SiC, etc. were used for the base substrate. Attempts were made in the 1960s to grow GaN using GaAs as the base substrate, but it did not grow well and ended in failure. Now, a thin buffer layer (20 nm to 80 nm) grown at low temperature is stacked on the base substrate and then epitaxially grown.

The above method is a method for growing a GaN thin film. It is not possible to make a thick film as it is. In the case of a thin film, since it is thin, it will not peel off even if there is a mismatch between the substrate and the thin film, but if GaN is deposited thickly, the internal stress will increase and it will peel off or wavy and cannot be thickened. Even if the film is thickened well, the dislocation density is high and the quality is low, so it is not usable. Therefore, the ELO method (Epitaxial Lateral Overgrowth) is used as a method to reduce the internal stress and reduce the dislocation density.

SiN, SiO₂Assuming that a film is formed on the base substrate and an equilateral triangle tile with a side of about 2 μm to 4 μm is spread on one side, a mask with a window with a diameter of 1 μm to 2 μm is made on the part corresponding to the apex of the equilateral triangle. GaN is vapor-grown from. Initially, GaN crystals grow from the underlying substrate of the window, which crawls onto the mask and grows sideways. It collides with the GaN crystal growing from the adjacent window, and after that, it becomes a uniform upward flat surface growth (C-plane growth). Dislocations extend laterally on the mask and collide from the left and right, reducing dislocations on the mask. The high dislocation density on the window remains the same, but the dislocations on the mask (cover) are lower. Although there are many ELO documents, Patent Documents 1 and 2 describe ELO on a GaAs substrate.

A self-supporting GaN crystal substrate can be obtained by growing a GaN crystal thickly with ELO and removing the GaAs substrate. A thicker GaN crystal can be made with ELO and the GaAs substrate can be removed to obtain a thick GaN ingot, which can be sliced into thin wafers to obtain multiple GaN free-standing crystal substrates. Patent Document 3 shows such a method.

What has been described above is a prior art for the growth of GaN crystals. Here, the story changes completely and describes off-angle crystals. Off-angle substrates were sometimes required for both Si and GaAs. In terms of GaAs, a (100) plane-just substrate is common, but when a thin film is grown on a just-plane substrate, the surface of the thin film may undulate and not necessarily become a smooth plane. Therefore, the substrate may be tilted slightly from (100) just, and a thin film may be grown on it to make a device. Such a slight inclination of the surface from the low surface index is called an off-angle (off-angle), and such a substrate is called an off-angle substrate. The tilt angle is called the off angle.

This is not always the case, and depending on the purpose, an off-angle substrate may be suitable. If you tilt it too much, the cleavage plane will shift, so you can make something that is tilted at a slight angle. Off-angle is common with existing semiconductor substrates such as Si, GaAs, and InP. There are various theories even in the optimum range of off-angle, and there is no established theory. The ones listed in Patent Documents 4 to 9 relate to off-angle substrates such as GaAs and InP. In addition to these, there is a large amount of off-angle literature on Si, GaAs, and InP.

In the case of GaAs and InP, a long and large (100) crystal ingot can be obtained by the HB method or LEC method, so cut diagonally with an inner peripheral blade slicer, outer peripheral blade slicer, wire saw, etc. in the direction diagonally intersecting the axis. To obtain an off-angle wafer. Since the ingot is long, there is no waste even if it is cut diagonally.

There is no demand for off-angle GaN substrates because GaN substrates are still poorly large and of high quality on the market. There is no off-angle GaN substrate, and there is no literature on which GaN was grown. Therefore, it is not clear whether off-angle GaN has better surface morphology when a thin film is grown on it than a just GaN substrate. However, there is literature that a GaN thin film was grown on an off-angle sapphire substrate.

In Patent Document 10, it is difficult to grow a p-type GaN thin film, but a sapphire substrate (α-Al) having an off-angle from the (0001) plane.₂O₃), It is stated that a p-type GaN crystal thin film can be formed by growing GaN by the MOCVD method. Finally, only the GaN thin film is placed on the sapphire. It is not stated whether the p-type thin film is intended, thick crystals are not intended, and the GaN thin film is off-angle.

Patent Document 11 describes a stepped off-angle sapphire substrate (α-Al).₂O₃By growing a GaN thin film on) by the MOCVD method, the active layer becomes like quantum dots and quantum wires, and carriers and light are effectively confined, so the output is enhanced and the life is extended. GaN is thin and does not aim to make substrates. It does not say whether GaN is off-angle.

Non-Patent Document 1 describes a (0001) sapphire substrate (α-Al) having an off angle of 0.03 ° to 0.25 °.₂O₃) With a thin (4 μm) growth of GaN, it states that surface morphology is improved (roughness is reduced) and EL (electroluminescence) is also improved. It does not form a thick film of GaN, but the GaN thin film remains attached to the sapphire substrate. The orientation of the GaN thin film is not mentioned.

Non-Patent Document 2 states that when a GaN thin film is grown on a 3.5 ° off-angle (0001) 4H-SiC substrate by the MOCVD method, the surface morphology is higher than that grown on a (0001) just SiC substrate. It says that it will improve and PL (photoluminescence) will increase. However, GaN is thin and does not form a substrate crystal. It remains attached to the SiC substrate. The crystal orientation of GaN is not stated.

<p> It does not mean that off-angle GaN substrates are required, but it is expected that off-angle substrates will be required as in the case of GaAs and InP substrates. A GaN thin film grown on an off-angle GaN substrate may be of higher quality than a GaN thin film grown on a just GaN substrate. I don't know yet, but off-angle GaN substrates may be requested for some reason.</p><p> In that case, if a single crystal growth from the liquid phase (HB method or LEC method) is possible like GaAs or InP and a long and large diameter single crystal ingot can be made, cut it with an inclination angle. It's good. Off-angle wafers can be easily made. However, in the case of GaN crystals, it is not possible to grow long single crystal ingots from the liquid phase. GaN is grown on a single crystal substrate of a dissimilar material to obtain a GaN crystal with some thickness, and the substrate is removed to form a GaN ingot, which is then cut diagonally to form an off-angle GaN wafer. Will do.</p><p> However, it is not desirable because there are many parts that are wasted. For example, suppose you want to make a GaN wafer with a diameter of 2 inches (51 mm) and a thickness of 500 μm with an off angle of 5 °. Since 51sin5 ° = 4.4, a GaN ingot with a height of 4.9 mm is made with a cutting allowance and cut at an inclination angle of 5 ° to obtain one off-angle wafer. From a 4.9 mm high ingot to a just 500 μm thick substrate, 9 sheets can be taken, so 8 sheets are wasted. Such drawbacks become more pronounced as the off-angle increases. At present, the GaN produced by the vapor phase growth method is thin, so such a drawback is serious.</p><p> If a thicker GaN single crystal ingot with a height of 30 mm can be made, even if an off-angle wafer of about 1 ° to 3 ° is taken, the loss is small, but at present, it is not possible to make such a thick GaN crystal. It takes a long time to make a product with a thickness of about 1 mm, and finally a product with a thickness of 10 mm can be made.</p><p> At present, a GaN single crystal has a large area, but only a thin crystal can be formed. Therefore, (0001) If just GaN is cut diagonally, the loss is large. And there is another problem. GaN grows slowly by vapor phase growth, but the dislocation density changes as it grows. In the case of a GaN crystal in which the dislocation density is high at the beginning of growth but the dislocation density decreases with growth, if it is cut diagonally, the dislocation density becomes significantly non-uniform in the plane.</p>

<p> In the present invention, an off-angle (111) GaAs crystal substrate is used, and GaN is thickly vapor-deposited on the GaAs crystal substrate to remove the GaAs substrate. Then, an off-angle GaN crystal substrate can be obtained. In the present invention, an off-angle (111) GaAs crystal substrate is further used, and GaN is vapor-deposited on the substrate to a thickness corresponding to a plurality of sheets to remove the GaAs substrate to obtain a GaN ingot, which is used as a growth axis. A plurality of off-angle GaN substrate crystals can be produced at once by slicing on an off-angle plane orthogonal to.</p><p> Alternatively, the ELO method is used to attach a mask with a large number of periodically (1 μm to 4 μm period) windows to an off-angle (111) GaAs substrate and vapor-deposit the GaN. Alternatively, a facet growth method in which a stripe mask or a dodd-shaped mask having a larger period (30 μm to 400 μm) is attached to generate and maintain facets can also be applied to the present invention.</p><p> The present invention will be described more specifically. As already mentioned, gallium nitride crystal growth includes vapor phase growth methods such as the HVPE method, MOC method, MOCVD method, and sublimation method. The present invention can be carried out by any method. Here, the HVPE method is used (the outline is shown in Fig. 2). The HVPE method used here is the following method.</p><p>A quartz boat containing Ga metal is installed in the upper part of a hot wall type furnace, and a base substrate is held and heated by a susceptor below the furnace, and hydrogen-diluted HCl is poured from above the furnace. , Ga + HCl GaCl reaction occurs at a high temperature of 800 ° C or higher, GaCl gas flows downward, and NH carried by hydrogen gas below.₃GaCl + NH by gas and GaCl₃ Causes a GaN reaction to generate GaN and deposit GaN on a heated substrate. The HVPE method has the advantages of high growth rate, low carbon pollution, and relatively simple equipment. It is the best method for making bulk crystals of GaN.</p><p>However, the present invention can also use a vapor phase growth method such as a MOCVD method, a MOC method, or a sublimation method. The basis of the present invention is to use an off-angle GaAs substrate as a substrate, vapor-deposit a GaN single crystal on the GaAs substrate, remove the GaAs substrate, and make the GaN self-supporting with an off-angle. It means to make a crystal substrate.</p><p> The present inventor has found that an off-angle GaN single crystal can be formed by vapor-depositing GaN using an off-angle GaAs single crystal as a base substrate. This is a completely new finding. Utilizing this principle, the present invention manufactures an off-angle GaN substrate by using an off-angle GaAs substrate as a base substrate and vapor-depositing GaN on the substrate. What is more important is that the off-angle direction and tilt angle of GaN can be completely specified by the orientation and tilt angle of the GaAs substrate of the base substrate. Therefore, the present invention can manufacture a GaN crystal substrate having an arbitrary orientation and an arbitrary inclination angle.</p><p> Of course, off-angle GaN crystals can be produced by growing them directly on an off-angle GaAs (111) substrate. Off-angle GaN can also be manufactured from off-angle GaAs substrates using a variety of other techniques.</p><p> A mask (SiO) with a large number of periodically distributed small windows on a (111) GaAs substrate with off-angles.₂, SiN) can be attached and GaN is vapor-deposited on top of it so that the dislocations extend laterally so that the dislocation density is low in the upper part of the mask. That is, the ELO method already described can be applied to off-angle substrates. Off-angle GaN also grows on the off-angle (111) GaAs substrate by the ELO method using a mask. Moreover, the off-angle and off-angle orientation are also determined.</p><p> To perform the ELO method, a GaN buffer layer (20 nm to 80 nm) may be thinly grown on an off-angle (111) GaAs substrate and then masked. Even in that case, off-angle GaN crystals can be grown. When a GaN crystal of appropriate thickness has grown, the substrate and mask are removed. Then, a GaN free-standing crystal with an off-angle is formed. Since ELO is used, one with fewer dislocations can be obtained.</p><p> Furthermore, a larger SiO on the base substrate₂Crystal growth is performed while maintaining facets with a SiN pattern (stripes, dots), and dislocations are swept up to the part that grows from the coating to serve as a gathering place for dislocations, and the part above the remaining mask opening is low. A faceted growth method for dislocation may be used.</p>

<p> In the present invention, as shown in FIG. 4, a GaN single crystal is grown on an off-angle (111) GaAs base substrate and the single crystal is cut at right angles to the growth axis to obtain a GaN wafer having a desired off-angle. There is little waste because the slices should be sliced at right angles to the growth axis rather than diagonally to the axis. In many cases, only thin crystals can be formed, so the effect is great. For example, suppose that a 2-inch diameter (0001) just 1000 μm-thick GaN crystal is made to take a 400 μm-thick wafer.</p><p>If it is just a wafer, you can take two wafers even if you include the cutting allowance. Only one wafer with a thickness of 400 μm with an off-angle of 1 ° can be taken. It is not possible to take even one GaN wafer with a 2 ° off angle and a thickness of 400 μm. However, in the present invention, when a 2 ° off-angle wafer is desired, 2 ° off-angle GaN is grown on a 2 ° off-angle GaAs substrate from the beginning, so a crystal with a thickness of 1000 μm to a thickness of 400 μm You can get two 2 ° off-angle wafers. Since GaN wafers are extremely expensive, the effect is great.</p><p> Furthermore, since the dislocation density of GaN crystals may differ significantly between the beginning, middle and end of growth, the dislocation density may change significantly depending on the wafer site when cut diagonally, but the present invention cuts at right angles to the growth axis. Therefore, since the growth time is the same on the wafer surface, there is little fluctuation such as dislocation density and the quality is constant.</p><p> Although there is such an effect, the value of the present invention is more than that, the discovery of predictability that the off-angle and off-angle directions of the GaN crystal can be specified in advance depending on the off-angle and direction of the underlying substrate. It is in.</p><p> Since the GaAs substrate used as the base substrate by the present invention has a track record of nearly 20 years since mass production became possible and can be easily obtained at low cost, the present invention is in a situation where it is easy to carry out. Most of the products on the market are (100) just GaAs substrates, but since long (100) GaAs single crystal ingots can be manufactured by the LEC method, VB method, and HB method, cut them diagonally to make off-angle wafers. Is possible to manufacture.</p><p> The gist of the present invention is that (111) the off-angle α of the off-angle GaAs substrate and the off-angle β of the GaN grown on it are equal (β = α), and the inclination angle of GaN is uniquely determined by the inclination direction of GaAs. The direction of is to be decided. As is clear in the examples, (111) the normal of the GaAs substrate (which forms the angle of α with the [111] direction: α is the off angle) is orthogonal to [111] [11-2], [1-10]. The direction of the tilt angle can be expressed by how it is tilted with respect to the two directions of.</p><p> The GaN crystal grows so that the (0001) plane overlaps the (111) plane of GaAs. The direction of the inclination angle depends on how the normal direction of GaN (which forms the angle of β with [0001]) is inclined with respect to [1-100] and [11-20] orthogonal to [0001]. Can be expressed. Then, the present inventor states that when the GaAs substrate normal is tilted in the [11-2] direction, the GaN crystal normal is tilted in the [1-100] direction and the GaAs substrate normal is tilted in the [1-10] direction. At that time, we found that the normal of the GaN crystal tilted in the [11-20] direction. In other words, the [1-100] direction of GaN coincides with the [11-2] direction of GaAs, and the [11-20] direction of GaN coincides with the [1-10] direction of GaAs. And the GaAs [111] axis coincides with the GaN [0001].</p><p> Why does such a correspondence hold? I guessed the reason. FIG. 5 is a perspective view representing the crystal structure of GaN. This includes several cells, but multiple cells are shown because the symmetry of the hexagonal system is easy to understand. Large white circles are nitrogen atoms and small circles are Ga atoms. There is Ga in the center on the bottom surface, and Ga atoms are also present at the vertices of a regular hexagon centered on it. The direction connecting the 6 Ga from the center Ga on the bottom is counterclockwise, [2-1-10], [11-20], [-12-10], [-2110], [-1- 120], [1-210]. This is the direction of the Ga-Ga bond in GaN. The direction in which gallium atoms do not exist is [1-100].</p><p> FIG. 6 is a perspective view showing the crystal structure of GaAs. It is a cubic system and is a sphalerite type. Black circles are Ga and white circles are As. The Ga atom is bonded to the four Nearest Neighbors around the top, bottom, left, and right. The four bonding directions are [111], [1-1-1], [-11-1], and [1-1-1]. In this figure, the diagonal plane containing the three Ga is the (111) plane. Ga atoms correspond to 6 Ga atoms (not bonds) in the Second Nearest Neighbor, but their directions are [-110], [01-1], [10-1], [1]. -10], [0-11], [-101]. This is the direction of the Ga-Ga bond on the surface of (111) GaAs.</p><p> The directions connecting the six Ga at the vertices of the regular hexagon surrounding the Ga atom on the (111) plane of GaAs and the central Ga are the above [-110], [01-1], [10-1], [1- 10], [0-11], [-101], and the direction connecting the six Ga at the apex of the regular hexagon surrounding the Ga atom on the (0001) plane of GaN and the central Ga is the above [2-1]. -10], [11-20], [-12-10], [-2110], [-1-120], [1-210]. Ga is common between GaAs and GaN.</p><p>(111) Since Ga is arranged almost regularly on the surface even in off-angle GaAs, the Ga-Ga direction of GaAs and the Ga-Ga direction of GaN should be common. This means that at the GaAs / GaN boundary, GaAs [-110], [01-1], [10-1], [1-10], [0-11], [-101] are GaN [ It is equal to 2-1-10], [11-20], [-12-10], [-2110], [-1-120], [1-210]. For that reason, it is speculated that the slope of the GaAs normal with respect to [-110] and the slope of GaN with respect to [2-1-10] correspond perfectly.</p>

[A method for manufacturing an off-angle GaN substrate by growing a GaN crystal on a GaAs substrate having an off-angle with or without an ELO mask]

A GaN crystal was formed on an off-angle GaAs substrate by the following procedure, made into a self-supporting film, ground and polished, and the off-angle and crystallinity were examined.

An off-angle GaAs (111) A plane was used as the base substrate. GaAs is a zinc blende (ZnS) type, cubic crystal. The GaAs (111) plane is a plane with three-fold rotational symmetry. The GaAs (111) plane has a surface in which only Ga atoms are exposed and a surface in which only As atoms are exposed. The former is called (111) Ga side or (111) A side. The latter is called the (111) As plane or the (111) B plane. Here, it is used in a GaAs (111) crystal with the Ga side facing up.

Since the (111) Ga plane has three-fold symmetry, hexagonal crystals can be grown on it. However, strictly speaking, it is not the (111) Ga plane but the off-angle. (111) The crystal direction &lt;hkm&gt; that can exist on the plane satisfies h + k + m = 0. Among them, the low exponential crystal directions that are orthogonal to each other are &lt;11-2&gt; and &lt;1-10&gt;. Here, &lt;...&gt; is a set representation of directions, and [...] is an individual representation of directions. On the other hand, (...) is an individual representation of faces, and {...} is a set representation of faces. The set representation is a set of all planes or directions that are converted to each other by the symmetry operation of the crystal. The (hkm) plane of GaAs means that the minimum plane is the a / h, b / k, and c / m intercept lengths of the a-axis, b-axis, and c-axis. The exponents h, k, and m are the reciprocals of the contact pieces and are integers. The direction [hkm] means the normal direction of the (hkm) plane.

In the case of the hexagonal system, the c-axis direction is slightly different, and the previous three exponents have the intercept length a / that cuts the 120 ° axis (a-, b-, d-) defined on the c-plane. When h, b / k, and d / m, the previous three indices are hkm. The rule h + k + m = 0 always holds. The fourth exponent n is that the intercept whose plane cuts the c-axis is c / n. Therefore, the hexagonal plane can be specified by the 4-index (hkmn). The direction [hkmn] is defined as the normal of the plane (hkmn). It is the same as in the case of the cubic system.

The following 10 types of off-angles were used for the base substrate. (Group A) Five types with crystal orientation [111] tilted 0.3 °, 1 °, 5 °, 10 °, and 20 ° in the direction of &lt;1-10&gt; with respect to the normal vector on the substrate surface (B) Group) The crystal orientation [111] is tilted 0.3 °, 1 °, 5 °, 10 °, and 20 ° in the direction of &lt;11-2&gt; with respect to the normal vector on the substrate surface. All 5 types are off-angle. It is a GaAs substrate.

Then, GaN is grown by the epitaxial lateral overgrowth method (ELO method: epiaxial lateral overgrowth) in which some of these off-angle GaAs substrates are masked with the following patterns A and B, and some are ELO method. Was not used.

Pattern A = A parallel striped mask with a pitch of 8 μm and an opening width of 2 μm as shown on the left in Fig. 1 Pattern B = A square opening with a side of 2 μm as shown on the right of Fig. 1 with a side of 4 μm. A pattern in which equilateral triangles are laid out and provided at the vertices of an equilateral triangle with six-fold symmetry.

(A) Pattern A ELO mask formed on the GaAs substrate surface A. 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 ° in the &lt;1-10&gt; direction of the instep group. The inclined ones are the substrates 1 to 7. Boards 8 to 14 are those that are tilted 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 ° in the &lt;11-2&gt; direction of Group B.

(B) Pattern B ELO mask formed on the GaAs substrate surface B. 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 ° in the &lt;1-10&gt; direction of the instep group. The inclined ones are the substrates 15 to 21. Boards 22 to 28 are those that are tilted 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 ° in the &lt;11-2&gt; direction of Group B.

(C) Those that do not have any pattern, those by non-ELO method C are 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 in the &lt;1-10&gt; direction of the instep group. Boards 29 to 35 are those that are tilted. Boards 36 to 42 are those that are tilted 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 ° in the &lt;11-2&gt; direction of Group B.

<tables num="1"><img file="JP2005298319A_D0001.tif" /></tables>

A GaN crystal layer was grown on these substrates 1-42 off-angle GaAs substrates by the HVPE method. Figure 2 shows the HVPE device. A Ga boat 3 having a Ga metal is provided above the reaction tube (furnace) 2, and the GaAs substrate 5 is held by the susceptor 4 below. A heater 6 is provided around the reaction tube 2 to heat the entire reaction tube 2 and hold the Ga boat 3 and the susceptor 4 at a desired temperature. Upper 1st gas supply port 7 to H₂+ HCl gas is blown into the Ga boat to generate GaCl gas, and H from the upper second gas supply port 8₂+ NH₃Gas is blown onto the GaAs substrate 5 GaCl and NH₃GaN is synthesized from and grown on a GaAs substrate.

Growth of a GaN crystal on a GaAs substrate initially causes a thin buffer layer to grow at low temperature and a thick GaN epitaxial film at high temperature to grow on the buffer layer. The buffer layer has a thickness of 20 nm to 80 nm. When the mask is attached, it may be attached on the substrate or on the buffer layer. Further, the mask layer may be placed after the epitaxial layer is stacked on the buffer layer by about 0.4 μm to 10 μm. In this case, the buffer layer and the epitaxial layer are combined and laminated to 0.5 μm to 10 μm before forming the mask. The conditions for generating the buffer layer and epi layer are as follows.

[Cushion layer formation conditions] Growth method HVPE method NH₃Partial pressure 0.1atm (10000Pa) HCl Partial pressure 1 × 10^-3atm (100Pa) Growth temperature 500 ° C Growth time 60 minutes Growth film thickness 60 nm

[Conditions for formation of epilayer of thick film] Growth method HVPE method NH₃Partial pressure 0.2atm (20000Pa) HCl Partial pressure 3 × 10^-2atm (3000Pa) Growth temperature 1010 ° C Growth time 10 hours Growth film thickness 1.0mm

As shown on the left side of FIG. 3, a GaN thick film was grown under the above conditions using the GaAs substrates 1 to 42 as the substrate. The GaAs substrate was then removed by etching. As a result, a free-standing GaN crystal substrate with a thickness of 1 mm was obtained. The GaN crystals formed by the substrates 1 to 42 are called samples 1 to 42. In all of Samples 1 to 42, the GaN crystal was a single crystal. In all the samples, the surface of the GaN substrate was an uneven surface in which the (0001) plane (C plane) and facets were mixed. The back surface of each of Samples 1 to 42 was a flat surface.

What is important is that the GaN grew so that the orientation of the underlying off-angle GaAs substrate [111] and the orientation of the grown GaN thick film [0001] were parallel in all of Samples 1-42. The GaN [0001] orientation was tilted at an angle equal to the off-angle α of the GaAs substrate with respect to the normal line erected on the surface of the GaN substrate. GaN substrate [0001] The angle formed by the orientation with respect to the normal line erected on the surface is defined as the off-angle β of GaN. As a result of this experiment, β = α in all of Samples 1 to 42.

Moreover, not only was GaN [0001] (c-axis) parallel to GaAs [111] on the substrate, but a strict correspondence was maintained with respect to the orientation around the axis. This is an important finding.

A sample in which the direction [111] of the GaAs base substrate was inclined in the direction of GaAs &lt;1-10&gt;, that is, GaN was grown on the substrates 1 to 7, 15 to 21, 29 to 35 of the group A. The [0001] (c-axis) of the GaN single crystal was tilted in the &lt;-1-120&gt; direction by the same angle. It presupposes (necessary condition) β = α that the inclinations of the axes are the same, but exceeds the limitation of β = α. Therefore, it means that the &lt;1-10&gt; direction of GaAs = the GaN &lt;-1-120&gt; direction. In other words, the direction is also determined around the axis. What is expressed here using the equal sign (=) for the direction is that it is parallel. Since the length is not defined in the direction vector, the equal sign emphasizes that it is parallel.

A sample in which the direction [111] of the GaAs base substrate was inclined in the direction of GaAs &lt;11-2&gt;, that is, GaN was grown on the substrates 8 to 14, 22 to 28, and 36 to 42 of Group B. The [0001] (c-axis) of the GaN single crystal was tilted in the &lt;1-100&gt; direction by the same angle. It means that consistent crystal growth such as GaAs &lt;11-2&gt; = GaN &lt;1-100&gt; is achieved. It naturally results from β = α, which assumes that the inclinations of the axes are the same, from the precondition (necessary condition) and the above GaAs &lt;1-10&gt; = GaN &lt;-1-120&gt;.

Therefore, when GaN is grown on off-angle GaAs, both the axial direction and the axial orientation are uniquely determined by the GaAs orientation. To put it simply, there was an off-angle relationship such as GaAs [111] = GaN [0001] GaAs &lt;1-10&gt; = GaN &lt;-1-120&gt; GaAs &lt;11-2&gt; = GaN &lt;1-100&gt;. It was found by the experiment of the present inventor.

The correspondence between these planes and directions was found by measuring the off-angle and off-angle directions of the GaN crystal (0001) plane by the X-ray diffraction method. Since there is such a correspondence for all of the substrates / samples 1 to 42, it can be said that it will be so with certain reproducibility.

The radius of curvature of the warp of the GaN crystal substrates of these samples 1 to 42 was 5 m or more. Carrier concentration is n = 1 × 10¹⁸cm^-3~1×10¹⁹cm^-3Met. Electron mobility is 100-200 cm²It was / Vs. Such electrical properties are almost the same as, and comparable to, a GaN free-standing substrate made by vapor deposition on a conventional GaAs (111) just substrate.

The surface of the self-supporting GaN crystals of Samples 1 to 42 was ground with the flat portion on the back surface as a reference surface to remove irregularities and smooth the crystals. Further polishing was possible to produce a polished GaN substrate with off-angle. The inclination of these 42 types of polished wafers in the [0001] direction was examined by an X-ray surface inspection device. According to it, the magnitude and orientation of the substrate tilt were almost the same as those examined by X-ray diffraction when the self-supporting film GaN was used.

In other words, the flattened GaN samples 1 to 7, 15 to 21, 29 to 35 of the instep group are 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 ° in the &lt;-1-120&gt; direction. It was a tilted off-angle GaN crystal substrate.

Group B flattened GaN samples 8-14, 22-28, 36-42 tilted off 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 ° in the &lt;1-100&gt; direction. It was an angle GaN crystal substrate.

The crystallinity was uniform in the plane. This will be described by a specific example. Sample 18: A GaN substrate in which pattern B (equilateral triangle repetition) was formed on the &lt;1-10&gt; direction 5 ° inclined GaAs (111) A plane and GaN was grown on it. When this GaN sample 18 was measured, The GaN [0001] direction was tilted 4 ° 25min in the &lt;-1-120&gt; direction and 0 ° 07min in the &lt;1-100&gt; direction. In the previous explanation, sample 18 should be tilted 5 ° in the &lt;-1-120&gt; direction and 0 ° in the &lt;1-100&gt; direction, but it is a little different. It is a discrepancy caused by the warpage of the GaN thick film crystal and the measurement problem. However, the difference is subtle, and it is rather surprising that the off-angle GaAs of the initial substrate can accurately determine the off-angle of GaN.

Regarding the off-angle range, the [111] direction of the GaAs substrate is 0.1 °, 0.3 °, and 1 ° in the &lt;1-10&gt; direction (group A) and &lt;11-2&gt; direction (group B) from the normal, respectively. , 5 °, 10 °, 20 °, and 25 ° were used as the base substrate, and GaN samples were prepared by the above three types of manufacturing methods (pattern A, pattern B, and no pattern). It was confirmed that it is possible to grow up to an off-angle of 25 ° in either the A group or the B group in the tilt direction. Therefore, it was confirmed that it is possible to produce off-angle GaN crystals from 0 to 25 °.

If it exceeds 25 °, it is not possible to produce off-angle GaN crystals. (111) Since an off-angle substrate exceeding 25 ° was not available for GaAs, the present inventor has not yet conducted a GaN growth experiment on a GaAs substrate exceeding 25 °. Therefore, it is unknown whether the present invention is possible even for off-angles exceeding 25 °. It may or may not be possible.

[A method of manufacturing an off-angle GaN substrate by growing GaN thinly on a GaAs substrate having an off-angle and growing a GaN crystal on the ELO pattern with or without providing it]

In Example 1, an ELO mask was provided (or not provided) directly on the off-angle GaAs substrate, and GaN was epigrown on the ELO mask. In Example 2, a thin GaN epi layer was attached on an off-angle GaAs substrate, and an ELO mask was provided (or not provided) on the thin GaN epi layer, and GaN was epigrown on the ELO mask. In other words, GaN grows in two stages and ELO grows in the middle. The off-angle GaN crystal thus produced was ground and polished to obtain a smooth flat wafer, and the off-angle and crystallinity were examined.

As in Example 1, off-angle GaAs in which the GaAs [111] direction is tilted 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 ° in the &lt;1-10&gt; direction as the instep group. The board was prepared.

As Group B, we prepared off-angle GaAs substrates with the GaAs [111] direction tilted 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 ° in the &lt;11-2&gt; direction. A GaN buffer layer and an epi layer were stacked on such an off-angle GaAs (111) substrate in the same furnace under the following conditions to produce a GaN crystal layer having a film thickness of about 10 μm. The reason why it is as thin as 10 μm is to ensure the flatness of the epi layer surface.

[Cushion layer formation conditions] Growth method HVPE method NH₃Partial pressure 0.1atm (10000Pa) HCl Partial pressure 1 × 10^-3atm (100Pa) Growth temperature 500 ° C Growth time 60 minutes Growth film thickness 60 nm

[Conditions for epilayer formation] Growth method HVPE method NH₃Partial pressure 0.2atm (20000Pa) HCl Partial pressure 2 × 10^-3atm (200Pa) Growth temperature 1010 ° C Growth time 30 minutes Growth film thickness 10 μm

An ELO mask (patterns A and B) similar to that in Example 1 was formed on the off-angle GaN / GaAs crystal, or no mask was formed. Pattern A = Parallel striped mask with a pitch of 8 μm and an opening width of 2 μm and a covering width of 6 μm as shown on the left of Fig. 1 Pattern B = Six-fold symmetry in a pattern of 4 μm equilateral triangles as shown on the right of Fig. 1. A square opening with a side of 2 μm is provided at the apex of an equilateral triangle.

In addition to the above groups A and B, (a) pattern A ELO formed on a GaN film (b) pattern B ELO formed on a GaN film (c) ELO mask None

This makes 42 types of mask / GaN / GaAs combinations possible. Substrate 43 to 84 are defined by the combination of Table 2 in the same manner as in Example 1.<tables num="2"><img file="JP2005298319A_D0002.tif" /></tables>

A thick GaN epi-growth film was formed at high temperature on these 42 types of mask / GaN / GaAs composite substrates.

[Conditions for epilayer formation] Growth method HVPE method NH₃Partial pressure 0.2atm (20000Pa) HCl Partial pressure 3 × 10^-2atm (3000Pa) Growth temperature 1010 ° C Growth time 10 hours Growth film thickness 1.0mm

The GaAs substrate and mask were removed by etching from the 42 types of GaN / mask / GaN / GaAs composite substrates thus produced (samples 43 to 84). Then, a 1.0 mm thick self-supporting GaN crystal substrate was obtained.

The back surface of the GaN substrate was flat. The surface of the GaN substrate was an uneven surface in which the (0001) surface and facets were mixed.

The off-angle β of the GaN of samples 43 to 84 was also equal to the off-angle α of the GaAs substrate (β = α). Moreover, the &lt;1-10&gt; direction of GaAs and the &lt;-1-120&gt; direction of GaN matched, and the GaAs &lt;11-2&gt; direction and the GaN &lt;1-100&gt; direction matched.

Using the flat portion on the back surface of the GaN thick film crystal as a reference surface, the surface surface was ground to remove irregularities and smooth the surface. Furthermore, GaN thick film crystals were polished to produce an off-angle GaN polished substrate with a flat and smooth surface (see Fig. 3).

The inclination of this flat smooth GaN substrate in the [0001] direction was examined by an X-ray surface inspection device. Similar to Example 1, it was found that the surface of GaN was tilted in the intended direction at the same off-angle (β = α) as the off-angle of GaAs. The crystallinity of Samples 43 to 84 was uniform in the plane.

[Method of growing GaN thickly on a GaAs substrate with off-angle and cutting GaN crystals to produce multiple GaN wafers]

Similar to Example 1, the ELO masks of patterns A and B are formed or not formed on five different off-angle GaAs substrates that are inclined in two directions, and a thin buffer layer is used as the base substrate, and then a thin buffer layer. A thick (10 mm) epi layer was grown and cut parallel to the growth plane to prepare multiple off-angle GaN wafers, and their characteristics were investigated.

GaAs (111) plane A tilt angle: 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, 25 ° Group: GaAs [111] direction is tilted in the &lt;1-10&gt; direction. Group: GaAs [111] direction is inclined in &lt;11-2&gt; direction

(A) Pattern A ELO formed on a GaN film (B) Pattern B ELO formed on a GaN film (C) No ELO mask

Pattern A = A parallel striped mask with a pitch of 8 μm and an opening width of 2 μm as shown on the left in Fig. 1 Pattern B = A square opening with a side of 2 μm as shown on the right of Fig. 1 with a side of 4 μm. A pattern in which equilateral triangles are laid out and provided at the vertices of an equilateral triangle with six-fold symmetry.

<tables num="3"><img file="JP2005298319A_D0003.tif" /></tables>

As shown in the table above, there are 42 types of substrates. This is referred to as a substrate 85 to 126. Samples 85 to 126 are GaN crystals made from the substrate. First, a thin buffer layer is formed at low temperature, and then a thick epi layer is formed at high temperature.

[Cushion layer formation conditions] Growth method HVPE method NH₃Partial pressure 0.1atm (10000Pa) HCl Partial pressure 1 × 10^-3atm (100Pa) Growth temperature 500 ° C Growth time 60 minutes Growth film thickness 60 nm

[Conditions for epilayer formation] Growth method HVPE method NH₃Partial pressure 0.2atm (20000Pa) HCl Partial pressure 3 × 10^-3atm (300Pa) Growth temperature 1010 ° C Growth time 100 hours Growth film thickness 10mm

In this way, a composite substrate having a height of 10 mm or more of GaN / GaAs was obtained. For all samples, the off-angle β of GaN and the off-angle α of GaAs are equal (β = α). The direction of inclination was also the same, the GaAs &lt;1-10&gt; direction was equal to the GaN &lt;-1-120&gt; direction, and the GaAs &lt;11-2&gt; direction was equal to the GaN &lt;1-100&gt; direction.

The GaAs and mask were removed by etching. A 10 mm thick GaN free-standing crystal was obtained. The back surface of the GaN crystal was flat. The surface of the GaN crystal was an uneven surface in which the (0001) plane and facets were mixed. Using the flat portion on the back surface of these GaN ingots as a reference surface, the surface surface was ground to remove irregularities and smooth the surface. It became a cylindrical GaN ingot. The ingot was cut in the direction perpendicular to the back normal with a wire saw using the flat surface on the back as a reference plane. We were able to cut out 10 GaN wafers with a thickness of 400 μm.

These sliced wafers could be polished to produce off-angle GaN wafers. The inclination of the wafer in the [0001] direction was examined by an X-ray surface inspection device. In all the samples, it was confirmed that the wafer was an off-angle wafer tilted in the intended direction by the intended angle.

The crystallinity was uniform in the plane. According to the method of growing a thick film of GaN on an off-angle GaAs substrate and cutting it in parallel to the plane, a larger number of off-angle GaN wafers can be obtained. For example, in the present invention, 10 2-inch diameter GaN wafers having a thickness of 400 μm and a 5 ° off angle could be cut from a 10 mm thick ingot (substantially usable area of 7 mm).

However, when it is attempted to cut out a 5 ° off-angle 400 μm-thick wafer from a 10 mm-thick 2-inch diameter GaN free-standing crystal with no off-angle, the cut surface and the crystal back surface are not parallel and are tilted by 5 °. Therefore, only 5 5-degree off-angle wafers can be taken. The present invention, which creates an off-angle ingot from the beginning, is extremely useful in that respect as well. It is effective in reducing the cost of off-angle GaN wafers.

[Method of growing GaN on an off-angle GaN substrate to manufacture an off-angle GaN substrate]

The above-mentioned one is for growing GaN on an off-angle GaAs base substrate. In Example 4, a GaN substrate having an off-angle is used as the base substrate. Since there is a GaN substrate with an off-angle manufactured in Example 1, this is used as a seed crystal. That is, the base substrate has been off-angle GaAs until now, but here, off-angle GaN is used as the base substrate. So this is a homoepitaxial growth, not a heteroepitaxial growth.

Group A: GaN [0001] (c-axis) tilted in the &lt;-1-120&gt; direction Group B: GaN [0001] (c-axis) tilted in the &lt;1-100&gt; direction Tilt angle: There are 14 types of boards because they are 0.1 °, 0.3 °, 1 °, 5 °, 10 °, 20 °, and 25 °. The seven off-angles of the A group are the substrates 127 to 133, and the seven off-angle ones of the B group are the substrates 134 to 140.

<tables num="4"><img file="JP2005298319A_D0004.tif" /></tables>

ELO is not used because GaN becomes a seed crystal. The GaN substrate was cleaned.

(Cleaning conditions) Cleaning temperature 1000 ° C NH₃Partial pressure 0.4atm (40000Pa) Cleaning time 10 minutes The substrate surface was cleaned under these conditions. A thick film of GaN was grown directly at high temperature without sandwiching the low temperature buffer layer.

[Conditions for epi-growth] Growth method HVPE method NH₃Partial pressure 0.2atm (20000Pa) HCl Partial pressure 3 × 10^-3atm (300Pa) Growth temperature 1010 ° C Growth time 100 hours Growth film thickness 10mm

Through such epitaxial growth, a free-standing GaN ingot with a thickness of 10 mm could be produced. This GaN ingot was homoepitaxially grown, and grew by inheriting the crystal orientation of the GaN substrate of the underlying substrate as it was. Therefore, the off-angle β of the GaN in the growing portion is equal to the off-angle α of the underlying GaN. In addition, off-angle GaN with the c-axis tilted in the &lt;-1-120&gt; direction is also formed from the GaN substrate (boards 127 to 133) of the instep group whose c-axis is tilted in the &lt;-1-120&gt; direction. It was. The same was true for Group B (boards 134 to 140).

The back surface was flat, but the front surface was uneven (0001) and was a mixed surface of facets. The surface was ground to remove irregularities. The flat surface on the back surface was used as a reference surface and cut parallel to the back surface with a wire saw. We were able to cut out 10 wafers with a thickness of 400 μm. By polishing these wafers, it was possible to obtain a GaN polished substrate with an off-angle. Such wafers were examined for tilt in the [0001] direction by an X-ray surface inspection device. It was found that it has the same crystal orientation and off-angle as the seed crystal GaN.

[GaN film epi-growth on off-angle GaN substrate, LED fabrication]

A GaN epi layer was grown by the MOCVD method on the 1 ° off-angle GaN substrate produced in Example 1. The surface of the epi-grown on the C-plane just substrate having no off-angle had irregularities, but the GaN epi-layer grown on the off-angle GaN substrate of the present invention had improved morphology and became flat. It has become. This is an advantage of off-angle boards. A blue LED having InGaN as a light emitting layer was produced on the epi layer. The brightness of the LED made on the off-angle board was higher than that of the LED made on the just board. That is because the epi-layer morphology is good, which is due to the off-angle. Off-angle GaN substrates enable the production of brighter LEDs than C-plane just substrates.

<figref num="1">The figure of the ELO mask pattern formed as an ELO mask on a GaAs substrate in this invention. Pattern A is a stripe pattern in which the opening extending in parallel is 2 μm wide, the shielding portion is 6 μm wide, and the pitch is 8 μm. In pattern B, a square window with a side of 2 μm is opened at the apex of a repeating equilateral triangle in which equilateral triangles with a side of 4 μm are spread.</figref><figref num="2">A Ga reservoir is provided in the upper part of the hot wall type reactor, and a susceptor with a base substrate (wafer) is provided in the lower part. The Ga reservoir and the base substrate are heated by the surrounding heaters, and hydrogen-diluted HCl is blown from above. Reacts with Ga to produce GaCl, GaCl and NH₃The figure explaining the HVPE method which grows GaN on the base substrate by reacting.</figref><figref num="3">Manufacturing steps of Examples 1 and 2 in which an off-angle GaN crystal is obtained by forming a mask on an off-angle GaAs base substrate and vapor-growing GaN through the mask to remove the off-angle GaAs base substrate and the mask. And the production of Example 4 in which GaN is epitaxially grown on the off-angle GaN crystal thus produced as a base substrate to form a thick off-angle GaN crystal and sliced thinly to produce a large number of off-angle GaN. An explanatory diagram of the process and a low-temperature growth GaN buffer layer were attached to the off-angle GaAs base substrate, and a mask was further attached to grow GaN thickly, and the off-angle GaAs base substrate and the mask were removed to obtain an off-angle GaN crystal substrate. The explanatory view of the manufacturing process of Example 3.</figref><figref num="4">Off-angle (111) After growing off-angle GaN crystals thickly on a GaAs substrate by vapor phase deposition, the GaAs substrate is removed and cut in the direction perpendicular to the growth axis to wastelessly off-angle GaN crystal wafers. The figure for demonstrating the advantage of this invention which made to obtain.</figref><figref num="5">Atomic model diagram showing the crystal structure of GaN.</figref><figref num="6">Atomic model diagram showing the crystal structure of GaAs.</figref>

Code description

2 Reaction tube 3 Ga boat 4 Suceptor 5 GaAs substrate 6 Heater