Method for manufacturing a group 13 element nitride crystal layer and seed crystal substrate

Abstract

[Problem] To make it possible to further lower the dislocation density of a group 13 element nitride crystal layer when growing a group 13 element nitride crystal layer on a seed crystal substrate. [Solution] A seed crystal layer 3 composed of group 13 element nitride crystals selected from gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof is provided on an alumina 2 layer on a single crystal substrate 1. Irregularities such that the RMS value measured by atomic force microscope reaches 180-700 nm are formed on a surface 3a of the seed crystal layer 3 by annealing in a reducing atmosphere at a temperature of 950-1200°C (inclusive). A group 13 element nitride crystal layer 13 composed of group 13 element nitride crystals selected from gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof is grown on the surface 3a of the seed crystal layer 3.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a Group 13 element nitride crystal layer and a seed crystal substrate. [Background technology]

[0002] As light-emitting devices such as light-emitting diodes (LEDs) using single-crystal substrates, those in which various gallium nitride (GaN) layers are formed on sapphire (α-alumina single crystal) are known. For example, mass-produced devices have a structure in which an n-type GaN layer, a multiple quantum well layer (MQW) consisting of an InGaN quantum well layer and a GaN barrier layer alternately stacked on a sapphire substrate, and a p-type GaN layer are sequentially stacked on a sapphire substrate.

[0003] Patent Document 1 (Patent No. 6059061) describes forming an uneven surface on the surface of a base substrate made of Group 13 element nitride crystals by hydrogen annealing, and then growing a Group 13 element nitride crystal layer.

[0004] Patent Document 2 (Patent No. 6126887) describes a method of forming an uneven surface by treating the surface of a base substrate made of a Group 13 element nitride crystal layer with chlorine plasma etching, and then growing a Group 13 element nitride crystal layer.

[0005] Patent Document 3 (Patent No. 5667574) describes forming microsteps of specific dimensions on the surface of a base substrate made of a Group 13 element nitride crystal layer, and then growing a Group 13 element nitride crystal layer. Methods for forming the microsteps include dry etching, sandblasting, laser processing, and dicing.

[0006] Patent Document 4 discloses a gallium nitride crystal layer and a free-standing substrate having a specific microstructure. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent 6059061 [Patent Document 2] Patent 6126887 [Patent Document 3] Patent 5667574 [Patent Document 4] WO 2019 / 039207A1 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when a base substrate is treated according to these conventional techniques to form a textured surface and then a Group 13 element nitride crystal layer is grown thereon, the dislocation density at the surface of the Group 13 element nitride crystal layer is effectively reduced. However, with recent technological advances, further improvements in luminescence intensity are required, and this requires an even greater reduction in the dislocation density at the surface of the Group 13 element nitride crystal layer.

[0009] An object of the present invention is to further reduce the dislocation density of a Group 13 element nitride crystal layer selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof when the layer is grown on a seed crystal substrate. [Means for solving the problem]

[0010] A first aspect of the present invention is a seed crystal layer growing step of providing a seed crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on an alumina layer on the single crystal substrate; an annealing step of forming irregularities on the surface of the seed crystal layer by annealing in a reducing atmosphere at a temperature of 950°C or higher and 1200°C or lower, so that the RMS value measured by an atomic force microscope is 180 nm to 700 nm; growing a Group 13 element nitride crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the surface of the seed crystal layer; The present invention relates to a method for producing a group 13 element nitride crystal layer, characterized by comprising the steps of:

[0011] Moreover, the first aspect of the present invention is a seed crystal layer growing step of providing a seed crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the alumina layer; an annealing step of forming irregularities on the surface of the seed crystal layer by annealing in a reducing atmosphere at a temperature of 950°C or higher and 1200°C or lower, so that the RMS value measured by an atomic force microscope is 180 nm to 700 nm; The present invention relates to a method for producing a seed crystal substrate, characterized by comprising:

[0012] Moreover, a second aspect of the present invention is a seed crystal layer growing step of providing a seed crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on an alumina layer on the single crystal substrate; an etching step of etching the surface of the seed crystal layer without applying a bias voltage to the seed crystal layer, when forming recesses on the surface by chlorine plasma etching the surface of the seed crystal layer so that the C-face ratio is 10% or more and 60% or less; growing a Group 13 element nitride crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the surface of the seed crystal layer; The present invention relates to a method for producing a group 13 element nitride crystal layer, characterized by comprising the steps of:

[0013] Moreover, a second aspect of the present invention is a seed crystal layer growing step of providing a seed crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on an alumina layer on a single crystal substrate; an etching step of etching the surface of the seed crystal layer without applying a bias voltage to the seed crystal layer when forming recesses on the surface by chlorine plasma etching the surface of the seed crystal layer so that the C-face ratio is 10% or more and 60% or less. The present invention relates to a method for producing a seed crystal substrate, characterized by comprising:

[0014] Moreover, a third aspect of the present invention is a single crystal substrate made of a sapphire substrate; an alumina layer on the single crystal substrate; and The seed crystal substrate has a seed crystal layer formed on the alumina layer and made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof, and the surface of the seed crystal layer has a plurality of steps, the height difference of the steps being 0.2 to 2 μm, and the terrace width of the steps being 0.25 to 2.0 mm.

[0015] A third aspect of the present invention is a step of growing a Group 13 element nitride crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on a surface of the seed crystal layer of the seed crystal substrate plate. The present invention relates to a method for producing a group 13 element nitride crystal layer, characterized by comprising the steps of: [Effects of the Invention]

[0016] According to the present invention, an alumina layer is grown on a single crystal substrate, and then a seed crystal layer made of a Group 13 element nitride crystal is formed on the alumina layer.The seed crystal layer is then subjected to a specific surface treatment or steps of specific dimensions are formed on the surface of the seed crystal layer, thereby reducing the dislocation density on the surface of the Group 13 element nitride crystal layer. [Brief explanation of the drawings]

[0017] [Figure 1](a) shows a state in which an alumina layer 2, a seed crystal layer 3, and a Group 13 element nitride crystal layer 13 are provided on a single crystal substrate 1, and (b) shows the Group 13 element nitride crystal layer 13 separated from the single crystal substrate. [Figure 2] 1(a) is a schematic diagram showing a grain boundary in a seed crystal layer, FIG. 1(b) is a cross-sectional view showing a state of the seed crystal layer 3 after surface treatment, and FIG. 1(c) shows a state in which a Group 13 element nitride crystal layer 13 is provided on the seed crystal layer 3. [Figure 3] 1(a) is a perspective view showing steps 19 on the surface of the seed crystal layer 3 (the edges are parallel to the a-plane), and FIG. 1(b) is a plan view of FIG. 1(a). [Figure 4] 1(a) shows the mechanism of dislocation reduction by steps, and FIG. 1(b) is a perspective view showing steps 19 on the surface of the seed crystal layer 3 (the edges are parallel to the m-plane). [Figure 5] FIG. 1(a) is a plan view showing the surface of a seed crystal layer having a hexagonal pattern and a step with a concave shape in the center, and FIG. 1(b) is a cross-sectional view taken along the line A-A in FIG. [Figure 6] FIG. 1(a) is a plan view showing the surface of a seed crystal layer having a triangular pattern and a step with a concave shape in the center, and FIG. 1(b) is a cross-sectional view taken along the line B-B of FIG. [Figure 7] FIG. 1(a) is a plan view showing the surface of a seed crystal layer having a hexagonal pattern with a step having a protruding central portion, and FIG. 1(b) is a CC cross-sectional view of FIG. [Figure 8] 2 is a schematic diagram for explaining a cathodoluminescence image of the upper surface 13a of the group 13 element nitride crystal layer 13. FIG. [Figure 9] 1 is a scanning electron microscope photograph of a cross section perpendicular to the top surface of a group 13 element nitride crystal layer. [Figure 10] 1 is a schematic diagram showing a functional element 21 according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in further detail below with reference to the drawings as appropriate. FIG. 1(a) shows a composite substrate 14 in which an alumina layer 2, a seed crystal layer 3, and a Group 13 element nitride crystal layer 13 are provided on a single crystal substrate 1, and FIG. 1(b) shows the Group 13 element nitride crystal layer 13 separated from the single crystal substrate.

[0019] (single crystal substrate) The material of the single crystal substrate 1 is sapphire.

[0020] (alumina layer) Next, an alumina layer 2 is formed on the single crystal substrate 1, thereby obtaining a base substrate. The alumina layer 2 can be formed using known techniques, such as sputtering, molecular beam epitaxy (MBE), vapor deposition, mist CVD, sol-gel deposition, aerosol deposition (AD), or tape casting, followed by laminating an alumina sheet to the single crystal substrate. Sputtering is particularly preferred. If necessary, the alumina layer can be subjected to heat treatment, plasma treatment, or ion beam irradiation after formation. The heat treatment method is not particularly limited, and can be performed in air, vacuum, a reducing atmosphere such as hydrogen, or an inert atmosphere such as nitrogen or Ar. Heat treatment can also be performed under pressure using a hot press (HP) furnace, hot isostatic press (HIP) furnace, or the like.

[0021] Alternatively, an alumina layer may be formed by surface treatment of a sapphire substrate, and a seed crystal layer made of a nitride of a Group 13 element may be formed on this alumina layer.

[0022] (seed crystal layer) 1(a), a seed crystal layer 3 is provided on the alumina layer 2 prepared as described above. The seed crystal layer 3 is subjected to a surface treatment to obtain a seed crystal substrate 10.

[0023] The material constituting the seed crystal layer 3 is a nitride of one or more of the group 13 elements defined by IUPAC. The group 13 elements are preferably gallium, aluminum, or indium. Specific examples of group 13 element nitride crystals include GaN, AlN, InN, Ga x Al 1-x N(1>x>0), Ga x In 1-x N(1>x>0), Ga x Al y InN 1―x-y (1>x>0, 1>y>0) is preferred.

[0024] The method for producing the seed crystal layer 3 is not particularly limited, but preferred examples include gas phase methods such as MOCVD (metal organic chemical vapor deposition), MBE (molecular beam epitaxy), HVPE (hydride vapor phase epitaxy), and sputtering; liquid phase methods such as the Na flux method, ammonothermal method, hydrothermal method, and sol-gel method; powder methods utilizing solid phase growth of powder; and combinations of these. For example, the seed crystal layer is preferably formed by MOCVD by depositing a low-temperature-grown buffer GaN layer to a thickness of 20 to 50 nm at 450 to 550° C., followed by laminating a GaN film to a thickness of 2 to 4 μm at 1000 to 1200° C. If a thicker seed crystal layer is required, it is preferably formed by, for example, using HVPE by depositing a low-temperature-grown buffer GaN layer to a thickness of 20 to 50 nm at 450 to 550° C., followed by laminating a GaN film to a thickness of 4 to 500 μm at 1000 to 1200° C.

[0025] (Surface treatment and surface morphology of the seed crystal layer) According to any one of the first, second and third aspects of the present invention, the surface of the seed crystal layer is treated.

[0026] (Surface treatment according to the first embodiment) In the first embodiment, the seed crystal layer is annealed in a reducing atmosphere at a temperature of 950°C or higher and 1200°C or lower, thereby forming irregularities on the surface 3a of the seed crystal layer 3 so that the RMS value measured with an atomic force microscope is 180 nm to 700 nm, thereby obtaining a composite substrate 14.

[0027] The reducing atmosphere gas is preferably one containing hydrogen gas as a main component. For example, it is preferable to use a mixed gas containing 50% or more hydrogen gas by volume, with the remainder being an inert gas (such as nitrogen gas). Alternatively, ammonia gas or the like may be used, or a mixture of these gases may be used. The annealing temperature is preferably 950°C to 1200°C. The annealing time may be selected as appropriate, but a preferred example is 5 to 60 minutes.

[0028] When such annealing is performed, the surface of the seed crystal layer, which was previously flat at the atomic level, becomes uneven. The uneven surface may have regular or periodic unevenness, or may have an irregular structure with randomly distributed large and small protrusions. The root-mean-square roughness (RMS) of the uneven surface is preferably 180 nm to 700 nm. The root-mean-square roughness (RMS) of this uneven surface is evaluated by measuring an area of ​​25 μm × 25 μm with an atomic force microscope (AFM) and analyzing the measurement results.

[0029] If the annealing temperature is lower than 950°C, the dislocation density reduction effect is not sufficient. This is thought to be because annealing under these conditions does not provide a sufficient uneven structure. Furthermore, if the temperature is higher than 1200°C, abnormal growth areas appear. This is thought to be because unevenness is formed to the extent that a Group 13 element nitride crystal layer cannot be formed.

[0030] (Surface treatment according to the second embodiment) According to the second embodiment, the surface 3 a of the seed crystal layer 3 is etched by chlorine plasma to form recesses on the surface so that the C-face ratio is 10% or more and 60% or less, and the surface of the seed crystal layer is etched without applying a bias voltage to the seed crystal layer.

[0031] Specifically, dislocations d (d0) exist within the seed crystal layer 3 in the thickness direction, as shown in Figure 2(a). This seed crystal layer is subjected to chlorine plasma etching. Chlorine gas is converted into a plasma state using ICP (Inductively Coupled Plasma) to etch the surface of the seed crystal layer. As a result, as shown in Figure 2(b), recesses 3c are formed on the surface of the seed crystal layer 3, and flat surfaces 3b remain between the recesses 3c. In typical ICP plasma etching, a bias voltage is applied to the workpiece. However, in this embodiment, no bias voltage is applied to the seed crystal layer. This is to suppress collisions of ions in the plasma (Cl ions) with the workpiece, which occurs predominantly when a bias voltage is applied, and to allow etching to proceed primarily through chemical reactions between chlorine radicals and the seed crystal. As shown in Figure 2(c), dislocations d0 propagate in the Group 13 element nitride crystal layer as d1 and d2, and threading dislocations d decrease.

[0032] The recesses are formed on the surface of the seed crystal layer so that the C-plane ratio is 10% or more and 60% or less. From the viewpoint of reducing dislocation density, the C-plane ratio is more preferably 10% or more and more preferably 40% or less.

[0033] The actual C-face ratio p can be calculated by measuring the surface 3a after etching two-dimensionally using a laser microscope or AFM (atomic force microscope), and applying a known image processing method to the obtained measurement results (surface unevenness data).

[0034] To set the C-face ratio p to 10% or more and 60% or less, it is preferable to set the etching time in the range of 100 minutes or more and 280 minutes or less, with the gas flow rate of Cl gas supplied into the chamber set to 20 sccm to 80 sccm, the gas pressure in the chamber set to 0.8 Pa to 3 Pa, and the ICP power set to 200 W to 1000 W.

[0035] (Surface treatment according to the third embodiment) In the third embodiment, the surface 3a of the seed crystal layer 3 has a plurality of steps, the step height is 0.2 to 2 μm, and the step terrace width is 0.25 to 2.0 mm. This reduces the number of steps, thereby reducing the dislocation density of the Group 13 element nitride crystal layer 13 formed thereon.

[0036] The step height is set to 0.2 to 2 μm. If the step height is less than 0.2 μm, grain boundaries will not be generated when the Group 13 element nitride crystal grows, and the dislocation reduction mechanism may not be fully realized, which is not preferable. If the step height exceeds 2 μm, the number of inclusions caught in the grain boundaries or their vicinity will be too large, which is also not preferable.

[0037] The edges of the steps may be substantially parallel to the a-plane of the Group 13 element nitride crystal, substantially parallel to the m-plane, or may face in any other direction, but are preferably formed substantially parallel to the a-plane of the Group 13 element nitride crystal. When the edges of the steps are formed parallel to the a-plane, the grain boundaries extend at an angle closer to the c-plane than when the edges are formed parallel to the m-plane, which is preferable because a wider area is covered by the grain boundaries for the same growth thickness. Note that "substantially parallel to the a-plane" not only means being parallel to the a-plane but also includes being substantially parallel to the a-plane (for example, a direction forming an angle of less than 5° with the a-plane).

[0038] Each step can be formed by, for example, dry etching, sandblasting, laser, dicing, or the like.

[0039] For example, in the example shown in Figures 3(a) and (b), numerous steps 19 are regularly formed on the surface 3a of the seed crystal layer 3, and the edges of each step 19 are approximately parallel to the a-plane of the Group 13 element nitride crystal. The width and height of the steps satisfy the above conditions. As shown in Figure 4(a), the action of the steps makes it easier for dislocations to be absorbed at the grain boundaries.

[0040] In the example shown in FIG. 4(b), steps 19 are regularly formed on the surface of the seed crystal layer 3, and the edge of each step is parallel to the hexagonal m-plane of the Group 13 element nitride crystal layer.

[0041] Furthermore, the steps may be formed in a pattern that has a concave shape (concave shape) at the center when viewed from the longitudinal cross section of the seed crystal substrate and a point-symmetric shape when viewed from the surface of the seed crystal layer. Examples of point-symmetric shapes include polygons such as triangles, squares, pentagons, and hexagons. In the example of Figures 5(a) and (b), the pattern is a hexagon in which the edges of all the steps 19 are parallel to the a-plane. In the example of Figures 6(a) and (b), the pattern is a triangle in which the edges of all the steps 19 are parallel to the a-plane. In addition, in the example of Figures 7(a) and (b), the surface of the seed crystal layer has a protruding shape at the center.

[0042] (Group 13 element nitride crystal layer) In the present invention, a Group 13 element nitride crystal layer is grown on the seed crystal layer. The Group 13 element nitride crystal layer of the present invention is made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof, and has a top surface and a bottom surface. For example, as shown in Figure 1(b), the Group 13 element nitride crystal layer 13 has a top surface 13a and a bottom surface 13b facing each other.

[0043] The nitrides constituting the group 13 element nitride crystal layer are gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof. Specifically, GaN, AlN, InN, Ga x Al 1-x N(1>x>0), Ga x In 1-x N(1>x>0), Ga x Al y In z N(1>x>0, 1>y>0, x+y+z=1).

[0044] Particularly preferably, the nitride constituting the group 13 element nitride crystal layer is a gallium nitride-based nitride. x Al1-x N(1>x>0.5), Ga x In 1-x N(1>x>0.4), Ga x Al y In z N(1>x>0.5, 1>y>0.3, x+y+z=1).

[0045] The Group 13 element nitride may be doped with zinc, calcium, or other n-type or p-type dopants. In this case, the polycrystalline Group 13 element nitride can be used as a member or layer other than the substrate, such as a p-type electrode, an n-type electrode, a p-type layer, or an n-type layer. Preferred examples of p-type dopants include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), strontium (Sr), and cadmium (Cd). Preferred examples of n-type dopants include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O).

[0046] In a preferred embodiment, when the upper surface of the Group 13 element nitride crystal layer is observed by cathodoluminescence, it has a linear high-brightness light-emitting portion and a low-brightness light-emitting region adjacent to the high-brightness light-emitting portion, and the high-brightness light-emitting portion includes a portion extending along the m-plane of the Group 13 element nitride crystal. This means that the linear high-brightness light-emitting portion appears on the upper surface, and that the dopant component and trace components contained in the Group 13 element nitride crystal produce a concentrated linear high-brightness light-emitting portion. At the same time, the fact that the linear high-brightness light-emitting portion extends along the m-plane means that the dopant gathers along the m-plane during crystal growth, resulting in the concentrated linear high-brightness light-emitting portion appearing along the m-plane.

[0047] That is, when the upper surface 13a of the group 13 element nitride crystal layer is observed by cathode luminescence (CL), it has a linear high-brightness light-emitting portion 5 and a low-brightness light-emitting region 6 adjacent to the high-brightness light-emitting portion 5, as shown schematically in FIG.

[0048] However, observations using CL shall be carried out as follows: For CL observation, a scanning electron microscope (SEM) equipped with a CL detector is used. For example, when using a Hitachi High-Technologies S-3400N scanning electron microscope equipped with a Gatan MiniCL system, the measurement conditions are preferably as follows: an accelerating voltage of 10 kV, a probe current of 90, a working distance (WD) of 22.5 mm, and a magnification of 50x, with the CL detector inserted between the sample and the objective lens.

[0049] The high-intensity light-emitting portion and the low-intensity light-emitting region are distinguished from each other by observation using cathodoluminescence as follows. Image analysis software (e.g., WinROOF Ver. 6.1.3, manufactured by Mitani Corporation) is used to create a 256-level grayscale histogram of the brightness of images observed with CL at an accelerating voltage of 10 kV, a probe current of 90, a working distance (WD) of 22.5 mm, and a magnification of 50x, with the vertical axis representing frequency and the horizontal axis representing brightness (GRAY). Two peaks are observed in the histogram, and the brightness at which the frequency is lowest between the two peaks is defined as the boundary, with the higher side defined as the high-brightness light-emitting area and the lower side defined as the low-brightness light-emitting area.

[0050] Furthermore, on the upper surface of the group 13 element nitride crystal layer, a linear high-brightness light-emitting portion is adjacent to a low-brightness light-emitting region. As a result, adjacent low-brightness light-emitting regions are separated by the linear high-brightness light-emitting portion between them. Here, the linear high-brightness light-emitting portion refers to a state in which the high-brightness light-emitting portion extends in an elongated shape and forms a boundary line between adjacent low-brightness light-emitting regions.

[0051] Here, the line formed by the high-brightness light-emitting portion may be a straight line, a curved line, or a combination of a straight line and a curved line. The curved line may have various shapes such as an arc, an ellipse, a parabola, or a hyperbola. Furthermore, the high-brightness light-emitting portions may be continuous in different directions, or the ends of the high-brightness light-emitting portions may be cut off.

[0052] On the upper surface of the Group 13 element nitride crystal layer, the low-brightness light-emitting region may be an exposed surface of the Group 13 element nitride crystal grown underneath, and it spreads two-dimensionally in a planar shape. On the other hand, the high-brightness light-emitting portion is linear, but extends one-dimensionally like a boundary line separating adjacent low-brightness light-emitting regions. This is thought to be due to, for example, dopant components and trace components being expelled from the Group 13 element nitride crystal grown from below, gathering between adjacent Group 13 element nitride crystals during the growth process, and generating a linear, strong light-emitting portion between adjacent low-brightness light-emitting regions on the upper surface.

[0053] For this reason, there are no particular limitations on the shape of the low-brightness light-emitting region, which is usually planar and extends two-dimensionally. On the other hand, the line formed by the high-brightness light-emitting portion must be long and thin. From this perspective, the width of the high-brightness light-emitting portion is preferably 100 μm or less, more preferably 20 μm or less, and particularly preferably 5 μm or less. In addition, the width of the high-brightness light-emitting portion is usually 0.01 μm or more.

[0054] The ratio of the length to the width of the high brightness light emitting portion (length / width) is preferably 1 or more, and more preferably 10 or more.

[0055] Furthermore, from the viewpoint of the present invention, on the upper surface, the ratio of the area of ​​the high-brightness light-emitting portion to the area of ​​the low-brightness light-emitting region (area of ​​the high-brightness light-emitting portion / area of ​​the low-brightness light-emitting region) is preferably 0.001 or more, and more preferably 0.01 or more.

[0056] Furthermore, from the viewpoint of the present invention, on the upper surface, the ratio of the area of ​​the high-brightness light-emitting portion to the area of ​​the low-brightness light-emitting region (area of ​​the high-brightness light-emitting portion / area of ​​the low-brightness light-emitting region) is preferably 0.3 or less, and more preferably 0.1 or less.

[0057] In a preferred embodiment, the high-brightness light-emitting portion includes a portion extending along the m-plane of the Group 13 element nitride crystal. For example, in the example of FIG. 8, the high-brightness light-emitting portion 5 extends in a long, thin line shape and includes many portions 5a, 5b, and 5c extending along the m-plane. The direction along the m-plane of the hexagonal Group 13 element nitride crystal is specifically the [-2110], [-12-10], [11-20], [2-1-10], [1-210], or [-1-120] direction, and the high-brightness light-emitting portion 5 includes a portion of the side of a substantially hexagonal shape reflecting the hexagonal crystal. Furthermore, the linear high-brightness light-emitting portion extending along the m-plane means that the longitudinal direction of the high-brightness light-emitting portion extends along any of the [-2110], [-12-10], [11-20], [2-1-10], [1-210], or [-1-120] directions. Specifically, this includes the case where the longitudinal direction of the linear high-brightness light-emitting portion is preferably within ±1°, more preferably within ±0.3°, relative to the m-plane.

[0058] In a preferred embodiment, the linear high-brightness light-emitting portion on the upper surface extends generally along the m-plane of the Group 13 element nitride crystal. This means that the main portion of the high-brightness light-emitting portion extends along the m-plane, and preferably the continuous phase of the high-brightness light-emitting portion extends substantially along the m-plane. In this case, the portion extending in the direction along the m-plane preferably accounts for 60% or more of the total length of the high-brightness light-emitting portion, more preferably 80% or more, and may account for substantially the entire high-brightness light-emitting portion.

[0059] In a preferred embodiment, the high-brightness light-emitting portions form a continuous phase on the upper surface of the Group 13 element nitride crystal layer, and the low-brightness light-emitting regions form a discontinuous phase partitioned by the high-brightness light-emitting portions. For example, in the schematic diagram of Figure 8, the linear high-brightness light-emitting portions 5 form a continuous phase, and the low-brightness light-emitting regions 6 form a discontinuous phase partitioned by the high-brightness light-emitting portions 5.

[0060] However, the continuous phase means that the high-brightness light-emitting portions 5 are continuous on the upper surface, but it is not essential that all of the high-brightness light-emitting portions 5 are completely continuous, and it is acceptable for a small number of high-brightness light-emitting portions 5 to be separated from other high-brightness light-emitting portions 5 to the extent that it does not affect the overall pattern.

[0061] The term "dispersed phase" means that the low-brightness light-emitting region 6 is generally partitioned by the high-brightness light-emitting portions 5 and is divided into many disconnected regions. Even if the low-brightness light-emitting regions 6 are separated by the high-brightness light-emitting portions 5 on the upper surface, it is permissible for the low-brightness light-emitting regions 6 to be continuous within the Group 13 element nitride crystal layer.

[0062] In a preferred embodiment, the half-width of the (0002) plane reflection of the X-ray rocking curve on the top surface of the Group 13 element nitride crystal layer is 3000 seconds or less and 20 seconds or more. This indicates that the surface tilt angle is small on the top surface, and the crystal orientation is highly oriented overall, like a single crystal. Having the cathodoluminescence distribution described above and a microstructure with such highly oriented crystal orientation on the surface as a whole can reduce the characteristic distribution on the top surface of the Group 13 element nitride crystal layer, making it possible to uniformly adjust the characteristics of various functional devices provided thereon and also improving the yield of the functional devices.

[0063] From this viewpoint, the half-width of the (0002) plane reflection of the X-ray rocking curve at the upper surface of the Group 13 element nitride crystal layer is preferably 1000 seconds or less and 20 seconds or more, and even more preferably 500 seconds or less and 20 seconds or more. However, it is practically difficult to reduce the half-width of the (0002) plane reflection of the X-ray rocking curve at the upper surface of the Group 13 element nitride crystal layer to less than 20 seconds.

[0064] The (0002) plane reflection of the X-ray rocking curve is measured as follows. Using an XRD instrument (e.g., Bruker-AXS D8-DISCOVER), the measurement conditions are 40 kV tube voltage, 40 mA tube current, 0.1 mm collimator diameter, 3 mm antiscattering slit, ω = peak position angle ±0.3°, ω step width 0.003°, and counting time 1 s. For this measurement, a Ge(022) asymmetric reflection monochromator is used to convert CuKα radiation into collimated monochromatic light (half-width 28 s), and the measurement is preferably performed with the axis aligned at a tilt angle of approximately CHI = 0°. The half-width of the (0002) plane reflection of the X-ray rocking curve can be calculated by peak search using XRD analysis software (Bruker-AXS LEPTOS 4.03). The peak search conditions are preferably set to Noise Filter "10", Threshold "0.30", and Points "10".

[0065] In a preferred embodiment, no voids are observed in a cross section substantially perpendicular to the upper surface of the Group 13 element nitride crystal layer. That is, no voids (gaps) or crystal phases other than the Group 13 element nitride crystal are observed in the SEM photograph shown in Fig. 9. However, void observation is performed as follows.

[0066] Voids are observed when a cross section of the Group 13 element nitride crystal layer taken approximately perpendicular to its upper surface is observed with a scanning electron microscope (SEM). The "voids" are defined as gaps with a maximum width of 1 μm to 500 μm. For this SEM observation, a Hitachi High-Technologies S-3400N scanning electron microscope is used, for example. The measurement conditions are preferably an acceleration voltage of 15 kV, a probe current of "60", a working distance (WD) of 6.5 mm, and a magnification of 1700x. Furthermore, when a cross section of the Group 13 element nitride crystal layer is observed substantially perpendicular to the upper surface thereof using a scanning electron microscope (under the observation conditions described above), no obvious grain boundaries associated with structural macro-defects such as voids are observed. With such a microstructure, it is believed that when a functional element such as a light-emitting element is fabricated on the Group 13 element nitride crystal layer, the increase in resistance and characteristic variations that would be caused by obvious grain boundaries can be suppressed.

[0067] In a preferred embodiment, the dislocation density on the upper surface of the Group 13 element nitride crystal layer is 1×10 2 / cm 2 That's it, 1 x 10 6 / cm 2 This dislocation density is 1×10 6 / cm 2 From the viewpoint of improving the characteristics of functional devices, it is particularly preferable to set the dislocation density to 3×10 or less. 3 / cm 2 It is more preferable that the dislocation density is less than 0.015. This dislocation density is measured as follows.

[0068] Dislocation density can be measured using a scanning electron microscope (SEM) equipped with a CL detector. For example, when observing with CL using a Hitachi High-Technologies S-3400N scanning electron microscope equipped with a Gatan MiniCL system, dislocations are observed as black dots (dark spots) without emitting light. Dislocation density can be calculated by measuring the density of these dark spots. The measurement conditions are preferably a CL detector inserted between the sample and the objective lens, with an accelerating voltage of 10 kV, a probe current of 90, a working distance (WD) of 22.5 mm, and a magnification of 1200x.

[0069] In a preferred embodiment, the X-ray rocking curve of the (0002) plane reflection at the top surface of the Group 13 element nitride crystal layer has a half-width of 3000 seconds or less and 20 seconds or more, and the half-width of the (1000) plane reflection is 10000 seconds or less and 20 seconds or more. This indicates that the surface tilt angle and surface twist angle at the top surface are both small, and the crystal orientation is highly oriented overall, like a single crystal. Such a microstructure with a highly oriented crystal orientation overall at the surface can reduce the characteristic distribution at the top surface of the Group 13 element nitride crystal layer, making it possible to uniformly adjust the characteristics of various functional devices formed thereon and improving the yield of the functional devices.

[0070] In a preferred embodiment, the half-width of the (1000) plane reflection of the X-ray rocking curve on the top surface of the Group 13 element nitride crystal layer is 10,000 seconds or less and 20 seconds or more. This means that the surface twist angle on the top surface is very low. It also indicates that the crystal orientation is highly oriented as a single crystal as a whole. In addition to the cathodoluminescence distribution described above, if the microstructure has such a highly oriented crystal orientation on the surface as a whole, the characteristic distribution on the top surface of the Group 13 element nitride crystal layer can be reduced, making it possible to uniformly match the characteristics of various functional devices provided thereon and improving the yield of the functional devices.

[0071] From this perspective, the half-width of the (1000) plane reflection of the X-ray rocking curve on the upper surface of the Group 13 element nitride crystal layer is preferably 5000 seconds or less, more preferably 1000 seconds or less, and even more preferably 20 seconds or more. In reality, it is difficult to reduce this half-width to less than 20 seconds.

[0072] However, the (1000) plane reflection of the X-ray rocking curve is measured as follows. Using an XRD device (e.g., Bruker-AXS D8-DISCOVER), the measurement conditions are 40 kV tube voltage, 40 mA tube current, no collimator, a 3 mm antiscattering slit, a ω peak position angle range of ±0.3°, a ω step width of 0.003°, and a counting time of 4 seconds. For this measurement, a Ge (022) asymmetric reflection monochromator is used to collimate CuKα radiation (half-width 28 seconds), and the axis is preferably set at a tilt angle of approximately 88°. The half-width of the (1000) plane reflection of the X-ray rocking curve can be calculated by peak search using XRD analysis software (Bruker-AXS LEPTOS 4.03). The peak search conditions are preferably set to Noise Filter "10," Threshold "0.30," and Points "10."

[0073] The Group 13 element nitride crystal layer is formed to have a crystal orientation that roughly follows the crystal orientation of the seed crystal layer. The method for forming the Group 13 element nitride crystal layer is not particularly limited as long as it has a crystal orientation that roughly follows the crystal orientation of the seed crystal layer. Preferred examples of the method include a gas phase method such as MOCVD or HVPE, a liquid phase method such as a Na flux method, an ammonothermal method, a hydrothermal method, or a sol-gel method, a powder method using solid phase growth of powder, and a combination thereof. The Na flux method is particularly preferred.

[0074] When forming a Group 13 element nitride crystal layer by the Na flux method, it is preferable to vigorously stir the melt to mix it thoroughly and uniformly. Such stirring methods include, but are not limited to, rocking, rotating, and vibrating.

[0075] The formation of a Group 13 element nitride crystal layer by the Na flux method is preferably carried out by filling a crucible containing a seed crystal substrate with a melt composition containing a Group 13 metal, metallic Na, and optionally a dopant (for example, an n-type dopant such as germanium (Ge), silicon (Si), or oxygen (O), or a p-type dopant such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), or cadmium (Cd)), heating and pressurizing the crucible to 830 to 910°C and 3.5 to 4.5 MPa in a nitrogen atmosphere, and then rotating the crucible while maintaining the temperature and pressure. The holding time varies depending on the target film thickness, but may be approximately 10 to 100 hours.

[0076] Furthermore, it is preferable to grind the gallium nitride crystal thus obtained by the Na flux method with a grindstone to flatten the plate surface, and then smooth the plate surface by lapping using diamond abrasive grains.

[0077] (Method for Separating Group 13 Element Nitride Crystal Layer) The Group 13 element nitride crystal layer is then separated from the single crystal substrate to obtain a free-standing substrate including the Group 13 element nitride crystal layer.

[0078] Here, the method for separating the Group 13 element nitride crystal layer from the single crystal substrate is not limited. In a preferred embodiment, the Group 13 element nitride crystal layer is naturally peeled off from the single crystal substrate in a temperature-lowering step after the growth of the Group 13 element nitride crystal layer.

[0079] Alternatively, the Group 13 element nitride crystal layer can be separated from the single crystal substrate by chemical etching. The etchant used in chemical etching is preferably a strong acid such as sulfuric acid or hydrochloric acid, a mixture of sulfuric acid and phosphoric acid, or a strong alkali such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide. The temperature used in chemical etching is preferably 70° C. or higher.

[0080] Alternatively, the Group 13 element nitride crystal layer can be peeled off from the single crystal substrate by a laser lift-off method. Alternatively, the Group 13 element nitride crystal layer can be peeled off from the single crystal substrate by grinding. Alternatively, the Group 13 element nitride crystal layer can be peeled off from the single crystal substrate with a wire saw.

[0081] (Freestanding substrate) A free-standing substrate can be obtained by separating the Group 13 element nitride crystal layer from the single crystal substrate. In the present invention, the term "free-standing substrate" refers to a substrate that can be handled as a solid object without being deformed or broken by its own weight. The free-standing substrate of the present invention can be used as a substrate for various semiconductor devices such as light-emitting elements, but can also be used as a member or layer other than the substrate, such as an electrode (which can be a p-type electrode or an n-type electrode), a p-type layer, or an n-type layer. This free-standing substrate may further be provided with one or more other layers.

[0082] When the Group 13 element nitride crystal layer constitutes a freestanding substrate, the thickness of the freestanding substrate must be sufficient to provide the substrate with self-supporting properties, and is preferably 20 μm or more, more preferably 100 μm or more, and even more preferably 300 μm or more. There should be no upper limit to the thickness of the freestanding substrate, but from the viewpoint of manufacturing costs, a thickness of 3000 μm or less is realistic.

[0083] (composite substrate) With the Group 13 element nitride crystal layer provided on the single crystal substrate, the layer can be used as a template substrate for forming other functional layers without separating the Group 13 element nitride crystal layer.

[0084] (functional element) The functional element structure provided on the Group 13 element nitride crystal layer of the present invention is not particularly limited, but examples thereof include a light-emitting function, a rectifying function, and a power control function.

[0085] The structure of the light-emitting device using the Group 13 element nitride crystal layer of the present invention and the method for fabricating the same are not particularly limited. Typically, a light-emitting device is fabricated by providing a light-emitting functional layer on a Group 13 element nitride crystal layer. However, a light-emitting device may also be fabricated by using the Group 13 element nitride crystal layer as a member or layer other than the substrate, such as an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, or an n-type layer.

[0086] Figure 10 shows a schematic diagram of the layer structure of a light-emitting device according to one embodiment of the present invention. The light-emitting device 21 shown in Figure 10 comprises a free-standing substrate 13 and a light-emitting functional layer 18 formed on this substrate. This light-emitting functional layer 18 emits light based on the principle of a light-emitting device such as an LED when a voltage is applied via electrodes or the like.

[0087] The light-emitting functional layer 18 is formed on the substrate 13. The light-emitting functional layer 18 may be formed on the entire surface or a portion of the substrate 13. Alternatively, if a buffer layer (described later) is formed on the substrate 13, the light-emitting functional layer 18 may be formed on the entire surface or a portion of the buffer layer. The light-emitting functional layer 18 may have various known layer configurations that emit light based on the principles of light-emitting devices, such as LEDs, by appropriately providing electrodes and / or phosphors and applying a voltage. Therefore, the light-emitting functional layer 18 may emit visible light, such as blue or red, or may emit ultraviolet light either alone or in combination with visible light. The light-emitting functional layer 18 preferably constitutes at least a portion of a light-emitting device using a p-n junction. As shown in FIG. 10 , this p-n junction may include an active layer 18b between a p-type layer 18a and an n-type layer 18c. In this case, a double or single heterojunction (hereinafter collectively referred to as a heterojunction) may be used as the active layer, using a layer with a smaller band gap than the p-type and / or n-type layers. Furthermore, as one form of p-type layer-active layer-n-type layer, a quantum well structure with a thin active layer can be adopted. Needless to say, to obtain a quantum well, a double heterojunction should be adopted in which the band gap of the active layer is smaller than that of the p-type layer and the n-type layer. Alternatively, a multiple quantum well structure (MQW) in which multiple quantum well structures are stacked may be used. These structures can increase the light emission efficiency compared to a pn junction. Thus, the light-emitting functional layer 18 preferably includes a pn junction and / or heterojunction and / or quantum well junction with light emission function. Reference numerals 20 and 22 are examples of electrodes.

[0088] Therefore, the one or more layers constituting the light-emitting functional layer 18 can include at least one selected from the group consisting of an n-type layer doped with an n-type dopant, a p-type layer doped with a p-type dopant, and an active layer. The n-type layer, the p-type layer, and the active layer (if present) may be made of a material having the same main component, or may be made of materials having different main components.

[0089] The materials of the layers constituting the light-emitting functional layer 18 are not particularly limited as long as they grow in a manner that generally follows the crystal orientation of the group 13 element nitride crystal layer and have light-emitting properties. However, materials primarily composed of at least one material selected from gallium nitride (GaN)-based materials, zinc oxide (ZnO)-based materials, and aluminum nitride (AlN)-based materials are preferred, and may contain an appropriate dopant to control the p-type or n-type. Gallium nitride (GaN)-based materials are particularly preferred. Furthermore, the material constituting the light-emitting functional layer 18 may be a mixed crystal, for example, GaN solid-solubilized with AlN, InN, or the like, to control its band gap. Furthermore, as mentioned in the immediately preceding paragraph, the light-emitting functional layer 18 may be a heterojunction composed of multiple materials. For example, a gallium nitride (GaN)-based material may be used for the p-type layer, and a zinc oxide (ZnO)-based material may be used for the n-type layer. Alternatively, a zinc oxide (ZnO)-based material may be used for the p-type layer, and a gallium nitride (GaN)-based material may be used for the active layer and the n-type layer. The combination of materials is not particularly limited.

[0090] The method for forming the light-emitting functional layer 18 and the buffer layer is not particularly limited as long as it is a method that allows growth that generally follows the crystal orientation of the Group 13 element nitride crystal layer. Preferred examples include gas phase methods such as MOCVD, MBE, HVPE, and sputtering; liquid phase methods such as the Na flux method, ammonothermal method, hydrothermal method, and sol-gel method; powder methods that utilize solid phase growth of powder; and combinations of these. [Example]

[0091] (Examples and Comparative Examples of the First Aspect) (Comparative Example A1) (Fabrication of freestanding gallium nitride substrates) A 0.3 μm alumina layer 2 was formed on a φ2-inch diameter sapphire substrate 1 by sputtering, and then a gallium nitride underlayer was formed at 500°C by MOCVD, followed by forming a 2 μm thick seed crystal layer 3 made of gallium nitride, thereby obtaining a seed crystal substrate 10. No particular surface treatment was performed on this seed crystal layer. The RMS (root mean square roughness) of the seed crystal layer was 0.3 nm.

[0092] Next, this seed crystal substrate was placed in an alumina crucible in a nitrogen atmosphere glove box. Next, metallic gallium and metallic sodium were filled into the crucible so that Ga / Ga+Na (mol%) = 15 mol%, and the crucible was covered with an alumina plate. The crucible was placed in a stainless steel inner container, which was then placed in a stainless steel outer container that could accommodate it, and closed with a container lid equipped with a nitrogen inlet pipe. This outer container was placed on a turntable installed in the heating section of a crystal manufacturing apparatus that had been vacuum-baked in advance, and the pressure-resistant container was sealed with a lid. Next, the pressure-resistant container was evacuated to 0.1 Pa or less using a vacuum pump. Next, while adjusting the upper, middle, and lower heaters to heat the heating space to 870 °C, nitrogen gas was introduced from a nitrogen gas cylinder to 4.0 MPa, and the outer container was rotated clockwise and counterclockwise at a constant speed of 20 rpm around its central axis. The acceleration time was 12 seconds, the hold time was 600 seconds, the deceleration time was 12 seconds, and the stop time was 0.5 seconds. This state was maintained for 40 hours. After that, the pressure was naturally cooled to room temperature and reduced to atmospheric pressure, and the lid of the pressure vessel was opened and the crucible was removed from inside. The solidified metallic sodium inside the crucible was removed, and a composite substrate was obtained. A 600 μm thick gallium nitride single crystal was grown on the seed crystal layer. Next, the gallium nitride crystal layer was peeled off from the sapphire substrate side of the composite substrate by irradiating it with laser light.

[0093] (Measurement of dislocation density) Next, the dislocation density was measured on the top surface of the group 13 element nitride crystal layer. CL observation was performed, and the density of dark spots, which are dislocation locations, was measured to calculate the dislocation density. Five 80 μm × 105 μm visual fields were observed, and the average dislocation density was 3.4 × 10 4 / cm 2 It was.

[0094] (Examples A1 to A7, Comparative Examples A2 to A7) In Comparative Example A1, the surface of the seed crystal substrate was treated as follows, and a gallium nitride crystal layer was grown thereon. Specifically, the surface of the seed crystal layer was annealed in the atmosphere under the temperature, time, and pressure conditions shown in Table 1. In Comparative Example A7, the surface of the seed crystal substrate was inductively coupled plasma (ICP) etched with Cl gas at a pressure of 1 Pa for 2 minutes.

[0095] Then, for each example, the root mean square roughness (RMS) of the seed crystal layer surface after the surface treatment was measured using an atomic force microscope (AFM).

[0096] A gallium nitride crystal layer was then formed in the same manner as in Comparative Example A1. Cathodoluminescence measurement was performed on the resulting gallium nitride layer at an acceleration voltage of 15 kV, and the dislocation density on the surface was determined based on the obtained image. Furthermore, the presence or absence of abnormal crystal growth in each gallium nitride crystal layer was confirmed using a polarizing microscope. The results are shown in Table 1.

[0097] (Comparative example A8) A gallium nitride crystal layer was grown in the same manner as in Example A1, and its surface condition was evaluated. However, in Comparative Example A8, an alumina layer was not provided on the sapphire substrate, and a gallium nitride seed crystal layer was formed directly. Other tests were performed in the same manner as in Example A1.

[0098] [Table 1]

[0099] As described above, it has been found that the surface treatment according to the first aspect of the present invention, when combined with a seed crystal layer on an alumina layer and a specific gallium nitride crystal layer, produces particularly remarkable effects, namely, good crystal growth and a significantly lower dislocation density than expected.

[0100] (evaluation) Next, the top and bottom surfaces of each gallium nitride freestanding substrate were polished and then observed by CL using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL photographs confirmed bright white light-emitting areas inside the gallium nitride crystals. However, when the same field of view was simultaneously observed using the SEM, no voids or other defects were observed, confirming the growth of homogeneous gallium nitride crystals.

[0101] In addition, the gallium nitride freestanding substrate was cut into a cross section perpendicular to its top surface, the cut surface was polished, and CL observation was performed using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL image confirmed bright white light-emitting areas inside the gallium nitride crystal. However, when the same field of view was simultaneously observed with SEM, no voids or other defects were observed, confirming the growth of homogeneous gallium nitride crystals. In other words, in the cross section of the gallium nitride crystal layer, as with the top surface, bright light-emitting areas were present in CL observation, but in the SEM, no microstructures of the same shape or similar to the bright light-emitting areas seen in the CL photograph were present in the same field of view.

[0102] (Deposition of light-emitting functional layer by MOCVD method) Using the MOCVD method, an n-type layer having a Si atomic concentration of 5×10 was grown at 1050° C. on the top surface of the gallium nitride freestanding substrate of Example A1. 18 / cm 3 Next, a multi-quantum well layer was deposited at 750°C as the light-emitting layer. Specifically, five 2.5 nm well layers of InGaN and six 10 nm barrier layers of GaN were alternately stacked. Next, a p-type layer was deposited at 950°C until the Mg atomic concentration reached 1×10 19 / cm 3 After that, the substrate was removed from the MOCVD apparatus and subjected to a heat treatment at 800°C for 10 minutes in a nitrogen atmosphere to activate the Mg ions in the p-type layer.

[0103] (Fabrication of light-emitting element) Using photolithography and vacuum deposition, Ti / Al / Ni / Au films serving as cathode electrodes were patterned on the surfaces of the gallium nitride freestanding substrate opposite the n-GaN layer and p-GaN layer to thicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Subsequently, a heat treatment at 700°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as translucent anode electrodes were patterned on the p-type layer to thicknesses of 6 nm and 12 nm, respectively. Subsequently, a heat treatment at 500°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as anode electrode pads were patterned to thicknesses of 5 nm and 60 nm, respectively, on a portion of the top surface of the Ni / Au film serving as the translucent anode electrode. The substrate thus obtained was cut into chips, which were then mounted on a lead frame to obtain light-emitting elements with a vertical structure.

[0104] (Evaluation of light-emitting elements) One hundred randomly selected elements were subjected to I / V measurements by passing a current between the cathode and anode electrodes, and rectification was confirmed in 95 elements. Furthermore, when a forward current was passed through them, light emission at a wavelength of 460 nm was confirmed.

[0105] (Test results for the second aspect) Gallium nitride crystal layers of the comparative examples and examples shown in Table 2 were grown and various properties were measured. The results are shown in Table 2.

[0106] (Comparative Example A1) Comparative Example A1 is the same as the above, and is an example in which the surface treatment of the seed crystal layer in Example A1 was not performed. The C-plane ratio of this seed crystal layer surface was 100%. The number of dark spots and dislocation density were measured on the surface of the obtained gallium nitride crystal layer, and the results are shown in Table 2.

[0107] (Examples B1 to B5 and Comparative Examples B1 to B5) In Comparative Example A1, the surface of the seed crystal substrate was subjected to the following surface treatment, and a gallium nitride crystal layer was grown thereon in the same manner as in Comparative Example A1. Specifically, the surface of the seed crystal layer was subjected to chlorine plasma etching under each of the conditions shown in Table 2. However, the conditions other than the etching time were the same, but the etching time was different for each sample. The conditions for chlorine plasma etching were as follows: the gas flow rate of Cl2 gas supplied into the chamber was 35 sccm, the gas pressure in the chamber was 1 Pa, and the ICP power applied by the high-frequency power supply was 800 W. However, no bias voltage was applied in the example and comparative examples B1 to B4, but a bias voltage was applied in comparative example B5.

[0108] However, for each sample, before the gallium nitride layer was formed, surface roughness data of a 2 mm square area was obtained using a laser microscope, and the C-plane ratio was evaluated based on the results.

[0109] The surface of the obtained gallium nitride layer was visually inspected, and the state of gallium nitride crystal formation was qualitatively evaluated (whether it was formed over the entire surface, only partially, or not at all). For samples on which gallium nitride crystals were formed, cathodoluminescence measurements were performed at an accelerating voltage of 15 kV, and the dislocation density on the surface was determined based on the obtained image.

[0110] (Comparative example B6) A gallium nitride crystal layer was grown in the same manner as in Example B1, and its surface condition was evaluated. However, in Comparative Example B6, an alumina layer was not provided on the sapphire substrate, and a gallium nitride seed crystal layer was formed directly. Other than that, the same tests as in Example B1 were conducted.

[0111] [Table 2]

[0112] As described above, it has been found that the surface treatment according to the second aspect of the present invention, when combined with a seed crystal layer on an alumina layer and a specific gallium nitride crystal layer, produces particularly remarkable effects, namely, good crystal growth and a significantly lower dislocation density than expected.

[0113] (evaluation) Next, the top and bottom surfaces of each gallium nitride freestanding substrate were polished and then observed by CL using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL photographs confirmed bright white light-emitting areas inside the gallium nitride crystals. However, when the same field of view was simultaneously observed using the SEM, no voids or other defects were observed, confirming the growth of homogeneous gallium nitride crystals.

[0114] In addition, the gallium nitride freestanding substrate was cut into a cross section perpendicular to its top surface, the cut surface was polished, and CL observation was performed using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL image confirmed bright white light-emitting areas inside the gallium nitride crystal. However, when the same field of view was simultaneously observed with SEM, no voids or other defects were observed, confirming the growth of homogeneous gallium nitride crystals. In other words, in the cross section of the gallium nitride crystal layer, as with the top surface, bright light-emitting areas were present in CL observation, but in the SEM, no microstructures of the same shape or similar to the bright light-emitting areas seen in the CL photograph were present in the same field of view.

[0115] (Deposition of light-emitting functional layer by MOCVD method) Using the MOCVD method, an n-type layer having a Si atomic concentration of 5×10 was grown at 1050° C. on the top surface of the gallium nitride freestanding substrate of Example B1. 18 / cm 3 Next, a multi-quantum well layer was deposited at 750°C as the light-emitting layer. Specifically, five 2.5 nm well layers of InGaN and six 10 nm barrier layers of GaN were alternately stacked. Next, a p-type layer was deposited at 950°C until the Mg atomic concentration reached 1×10 19 / cm 3After that, the substrate was removed from the MOCVD apparatus and subjected to a heat treatment at 800°C for 10 minutes in a nitrogen atmosphere to activate the Mg ions in the p-type layer.

[0116] (Fabrication of light-emitting element) Using photolithography and vacuum deposition, Ti / Al / Ni / Au films serving as cathode electrodes were patterned on the surfaces of the gallium nitride freestanding substrate opposite the n-GaN layer and p-GaN layer to thicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Subsequently, a heat treatment at 700°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as translucent anode electrodes were patterned on the p-type layer to thicknesses of 6 nm and 12 nm, respectively. Subsequently, a heat treatment at 500°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as anode electrode pads were patterned to thicknesses of 5 nm and 60 nm, respectively, on a portion of the top surface of the Ni / Au film serving as the translucent anode electrode. The substrate thus obtained was cut into chips, which were then mounted on a lead frame to obtain light-emitting elements with a vertical structure.

[0117] (Evaluation of light-emitting elements) One hundred randomly selected elements were subjected to I / V measurements by passing a current between the cathode and anode electrodes, and rectification was confirmed in 91 of them. Furthermore, when a forward current was passed through them, light emission at a wavelength of 460 nm was confirmed.

[0118] (Experimental results of the third embodiment) (Comparative Example A1) Comparative Example A1 is the same as the above, and is an example in which the surface treatment of the seed crystal layer in Example A1 was not performed. No steps were provided on the surface of this seed crystal layer. The dislocation density of the resulting gallium nitride crystal layer surface was measured and is shown in Table 3.

[0119] (Examples C1 to C10 and Comparative Examples C1 to C4) A seed crystal substrate and a gallium nitride crystal layer were manufactured in the same manner as in Comparative Example A1, except that a gallium nitride underlayer was formed on an alumina layer at 500°C by HVPE, followed by a 350 μm-thick seed crystal layer 3 made of gallium nitride. However, after the seed crystal substrate was manufactured, the surface of the seed crystal layer was processed by reactive ion etching (RIE) to form regular steps with terrace widths and height differences as shown in Table 3. The edges of each step were parallel to the a-plane or m-plane of the gallium nitride crystal. The terrace width, arrangement, and direction of the step edges were controlled by the mask pattern used during RIE. The step height (depth) was adjusted by the RIE processing time.

[0120] A gallium nitride crystal layer was formed on the seed crystal substrate of each example in the same manner as in Comparative Example A1, and the dislocation density of the surface was measured. The results are shown in Table 3.

[0121] (Comparative example C5) A gallium nitride crystal layer was grown in the same manner as in Example C1, and its surface condition was evaluated. However, in Comparative Example C5, an alumina layer was not provided on the sapphire substrate, and a gallium nitride seed crystal layer was formed directly. Other tests were performed in the same manner as in Example C1.

[0122] [Table 3]

[0123] As described above, it has been found that the surface treatment according to the third aspect of the present invention, when combined with a seed crystal layer on an alumina layer and a specific gallium nitride crystal layer, produces particularly remarkable effects, namely, good crystal growth and a significantly lower dislocation density than expected.

[0124] (evaluation) Next, the top and bottom surfaces of each gallium nitride freestanding substrate were polished and then observed by CL using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL photographs confirmed bright white light-emitting areas inside the gallium nitride crystals. However, when the same field of view was simultaneously observed using the SEM, no voids or other defects were observed, confirming the growth of homogeneous gallium nitride crystals.

[0125] In addition, the gallium nitride freestanding substrate was cut into a cross section perpendicular to its top surface, the cut surface was polished, and CL observation was performed using a scanning electron microscope (SEM) equipped with a CL detector. As a result, the CL image confirmed bright white light-emitting areas inside the gallium nitride crystal. However, simultaneous SEM observation of the same field of view confirmed no voids or other defects, confirming the growth of homogeneous gallium nitride crystals. In other words, while the CL observation showed bright light-emitting areas in the cross section of the group 13 element nitride crystal layer, just like the top surface, the SEM observation showed no microstructures of the same shape or similar to the bright light-emitting areas seen in the CL photograph in the same field of view.

[0126] (Deposition of light-emitting functional layer by MOCVD method) Using the MOCVD method, an n-type layer having a Si atomic concentration of 5×10 was grown at 1050°C on the top surface of the gallium nitride freestanding substrate of Example C1. 18 / cm 3 Next, a multi-quantum well layer was deposited at 750°C as the light-emitting layer. Specifically, five 2.5 nm well layers of InGaN and six 10 nm barrier layers of GaN were alternately stacked. Next, a p-type layer was deposited at 950°C until the Mg atomic concentration reached 1×10 19 / cm 3 After that, the substrate was removed from the MOCVD apparatus and subjected to a heat treatment at 800°C for 10 minutes in a nitrogen atmosphere to activate the Mg ions in the p-type layer.

[0127] (Fabrication of light-emitting element) Using photolithography and vacuum deposition, Ti / Al / Ni / Au films serving as cathode electrodes were patterned on the surfaces of the gallium nitride freestanding substrate opposite the n-GaN layer and p-GaN layer to thicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Subsequently, a heat treatment at 700°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as translucent anode electrodes were patterned on the p-type layer to thicknesses of 6 nm and 12 nm, respectively. Subsequently, a heat treatment at 500°C in a nitrogen atmosphere was performed for 30 seconds to improve ohmic contact characteristics. Furthermore, using photolithography and vacuum deposition, Ni / Au films serving as anode electrode pads were patterned to thicknesses of 5 nm and 60 nm, respectively, on a portion of the top surface of the Ni / Au film serving as the translucent anode electrode. The substrate thus obtained was cut into chips, which were then mounted on a lead frame to obtain light-emitting elements with a vertical structure.

[0128] (Evaluation of light-emitting elements) 100 randomly selected elements were subjected to IV measurements by passing a current between the cathode and anode electrodes. 92 Rectification was confirmed for each of these. When a forward current was passed through them, light emission with a wavelength of 460 nm was confirmed.

Claims

1. a single crystal substrate made of a sapphire substrate; an alumina layer on the single crystal substrate; and a seed crystal layer formed on the alumina layer and made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof; The seed crystal substrate is characterized in that the surface of the seed crystal layer has a plurality of steps, the height difference of the steps is 0.2 to 2 μm, and the terrace width of the steps is 0.25 to 2.0 mm.

2. A step of growing a Group 13 element nitride crystal layer made of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the surface of the seed crystal layer of the seed crystal substrate according to claim 1.

1. A method for producing a group 13 element nitride crystal layer, comprising:

3. The method of claim 2 , wherein the edge of the step is formed substantially parallel to the a-plane of the group 13 element nitride crystal.

4. 4. The method according to claim 2, wherein when the upper surface of the group 13 element nitride crystal layer is observed by cathode luminescence, the layer has a linear high brightness light emitting portion and a low brightness light emitting region adjacent to the high brightness light emitting portion.

5. 5. The method according to claim 4, wherein the high-intensity light-emitting portion includes a portion extending along an m-plane of the group 13 element nitride crystal.

6. The method according to any one of claims 2 to 5, wherein the half width of the (0002) plane reflection of the X-ray rocking curve on the upper surface of the group 13 element nitride crystal layer is 3000 seconds or less and 20 seconds or more.

7. The method according to any one of claims 2 to 6, wherein no voids are observed in a cross section substantially perpendicular to the upper surface of the group 13 element nitride crystal layer.

8. 6. The method according to claim 4, wherein the high-intensity light-emitting portion forms a continuous phase, and the low-intensity light-emitting region forms a discontinuous phase partitioned by the high-intensity light-emitting portion.

9. The method according to any one of claims 2 to 8, wherein the half width of the (1000) plane reflection of the X-ray rocking curve on the upper surface of the group 13 element nitride crystal layer is 10,000 seconds or less and 20 seconds or more.

10. The method according to any one of claims 2 to 9, wherein the Group 13 element nitride crystal layer is separated from the surface of the seed crystal layer of the seed crystal substrate, thereby obtaining a free-standing substrate made of the Group 13 element nitride crystal layer.

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