Crack-free and low-dislocation crystal grown on a patterned substrate

Abstract

A method of suppressing cracks and reducing defect density by epitaxial growth of crystals on a layer having a pattern of shapes based on a crystal system and having different lattice constants, and a substrate obtained by the method. The main advantage is the ability to obtain crack-free AlGaN with low defect density on GaN or AlN substrates. In addition, since any material can be used for the base substrate, a low-cost substrate can be selected. Also, this method can be applied to other material systems.

Description

[0001] CRACK-FREE AND LOW-DISLOCATION CRYSTAL GROWN ON A PATTERNED SUBSTRATE

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit under 35 U.S.C. Section 1 19(e) of the following co-pending and commonly-assigned application:

[0004] U.S. Provisional Application Serial No. 63 / 697,146, filed on September 20, 2024, by Toru Inatome, Hsun-Ming Chang, Michael Iza, Yifan Yao, and Shuji Nakamura, entitled “CRACK-FREE AND LOW-DISLOCATION CRYSTAL GROWN ON A PATTERNED SUBSTRATE,” attorneys’ docket number G&C 30794.0860USP1 (UC-2025-342-1); which application is incorporated by reference herein.

[0005] BACKGROUND OF THE INVENTION

[0006] 1. Field of the Invention.

[0007] This invention is a method of suppressing cracks and reducing defect density by epitaxial growth of crystals on a layer having a pattern of shapes based on a crystal system and having different lattice constants, and a substrate obtained by the method.

[0008] 2. Description of the Related Art.

[0009] AlGaN (AlxGai xN wherein 0<x<l) is a material expected to be applied to optical devices, such as light-emitting diodes (LEDs) and lasers, power devices, radio frequency (RF) devices, etc. Its wide bandgap ranging from 3.4 to 6.2 eV depending on its chemical composition, makes it suitable as an optical device in the ultraviolet (UV) region. Moreover, this wide bandgap allows it to operate at higher frequencies, which, coupled with the high breakdown voltage of AlGaN, makes it ideal for RF devices that require high power and high frequency operation. The high breakdown voltage also makes AlGaN useful as a power device that requires operation at high voltages. AlGaN semiconductor devices are mainly fabricated by growing them on GaN or AIN bulk substrates or GaN or AIN on sapphire templates by MOCVD, but there are problems of cracks and dislocation defects due to lattice mismatch with the substrate materials. In particular, it is difficult to grow AlGaN with an Al ratio of 20% or more on GaN and with an Al ratio of less than 70% on AIN, without cracks.

[0010] Several methods have been proposed to suppress these issues, one of which is to grow AlGaN on GaN that has been fabricated into a stripe mask pattern. According to this method, the stripe-like space of GaN can alleviate the strain caused by the lattice mismatch of the material growing on it, and suppress the generation of cracks (See, H. Miyake, N. Matsuda, Y. Ogawahara, M. Narukawa, K. Hiramatsu, T. Ezaki, N. Kuwano, J. Ciyst. Growth. 2008, 310, 4885-4887.). Also, in this method, a mask material such as SiCh is deposited in stripes on the flat GaN, and a stripe pattern of GaN is created by growing GaN crystals only where there is no mask material using a method called Selective Area Growth (SAG), which reduces defect density by suppressing through-defects from the masked areas. On the other hand, this method has several issues, such as the fact that a large number of through-defects are concentrated on the crystal-grown stripe-shaped GaN, limiting the area that can be utilized as a device, and the defect density is still high.

[0011] In recent years, a method has been proposed to significantly reduce defect density by creating a hexagonal hole pattern that matches the shape of the crystal system of AIN and crystal-growing AIN on top of it (See, J. Wang, N. Xie, F. Xu, L. Zhang, J. Lang, X. Kang, Z. Qin, X. Yang, N. Tang, X. Wang, W. Ge, B. Shen, Nat. Mater. 2023, 22, 853-859.). According to this method, the hexagonal pattern can reduce defect density because the crystal growth rate from each side of the hexagon is uniform. However, it has not yet been reported to obtain a crack-free crystal by growing AlGaN with a different composition on a substrate with a hexagonal pattern. SUMMARY OF THE INVENTION

[0012] There has been no report yet on the growth of AlGaN with low defect density and no cracks on GaN or AIN substrates. Furthermore, not only in the above material system, but when growing materials with the same crystal system and different lattice constants epitaxially, there is a problem of cracks and defects caused by lattice mismatch between the grown crystal and the substrate.

[0013] Therefore, the present invention provides a method for growing a crystal with a low defect density while suppressing cracks on a substrate with a different lattice constant, and a substrate obtained by the method. One embodiment of the substrate of the present invention includes a base substrate, a first layer located on or above the base substrate, and an epitaxially grown second layer located on or above the first layer, wherein the first layer has a pattern that has the same shape of the crystal system of the material comprising the first layer in a plane parallel to the top surface of the first layer and the second layer comprises a material having the same crystal system as the first layer but a different lattice constant.

[0014] According to the present invention, it is possible to grow a high-quality crystal with few cracks and low defect density on a substrate with different crystal systems and different lattice constants.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Referring now to the drawings in which like elements represent corresponding parts throughout:

[0017] Figs. 1(a), 1(b), 1(c), 1(d), 1(e), 1(f), 1(g), 1(h), l(i) and l(j) are a process flow diagram that illustrates the experimental procedure of the present invention.

[0018] Fig. 2 is a cross-sectional schematic diagram of the substrate of the present invention, which has a substrate, a first layer with a hole pattern formed by etching, and a second layer. Fig. 3 is a cross-sectional schematic diagram of the substrate of the present invention, which has a substrate, a first layer with a mask pattern formed by depositing a mask material, and a second layer.

[0019] Fig. 4 is a cross-sectional schematic diagram of the substrate of the present invention, which has a substrate, a first layer with a hole pattern formed by depositing a mask material followed by crystal growth, and a second layer.

[0020] Fig. 5 is a scanning electron microscope (SEM) image of a GaN substrate with a hexagonal pattern created by the method described in Example 1.

[0021] Figs. 6(a) and 6(b) are optical microscope images of AlGaN deposited on hexagonal patterned GaN (Fig. 6(a)) and non-pattemed GaN on a sapphire substrate (Fig. 6(b)), created by the method described in Example 1.

[0022] Figs. 7(a) and 7(b) are cathodoluminescence (CL) results for AlGaN on patterned GaN on sapphire (Fig. 7(a)) and GaN on sapphire (Fig. 7(b)).

[0023] Fig. 8 is a flowchart illustrating a method of suppressing cracks and reducing defect density by epitaxial growth of crystals on a layer having a pattern of shapes based on a crystal system and having different lattice constants.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0026] Overview

[0027] This invention is a method of suppressing cracks and reducing defect density by epitaxial growth of crystals on a layer having a pattern of shapes based on a crystal system and having different lattice constants, and a substrate obtained by the method. Technical Description

[0028] The structure of the substrate according to this invention is comprised of a base substrate, a first layer comprised of a first material located on or above the base substrate, and an epitaxially grown second layer comprised of a second material located on or above the first layer, wherein: the first layer has one or more patterns that have the same shape as the crystal system of the first material in a plane parallel to a top surface of the first layer; and the second material of the second layer has the same crystal system as the first material but a different lattice constant.

[0029] Base Substrate

[0030] The material for the base substrate can be anything, including but not limited to 1I1-V group materials (InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs, AlAs, or alloys of III group and V group elements), VI group materials (Si, SiGe, SiC, C, or alloys of VI group elements), oxide materials (SiCh, AI2O3, TiCh, ZnO, (In, GafCh, or other oxide materials), and sapphire.

[0031] The material of the base substrate can be the same material as that of the first layer. By being the same, the lattice mismatch between the base substrate and the first layer material is reduced, resulting in fewer defects. Single-crystal substrates, such as GaN or AIN, can be used for the base substrate and the first layer, and the process of forming the first layer can be shortened by using single-crystal substrates such as GaN or AIN.

[0032] The base substrate material can be different from the material of the first layer. This allows for the selection of cheaper materials as the base substrate.

[0033] First Layer

[0034] The first material for the first layer can be anything, including but not limited to III-V group materials (InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs, AlAs, or alloys of III group and V group elements), VI group materials (Si, SiC, C, or alloys of VI group elements), or oxide materials (SiC>2, AI2O3, TiCh, ZnO, (In, Ga)20s, or other oxide materials), and sapphire.

[0035] The first material of the first layer has the same crystal system as the second material of the second layer but with a different lattice constant.

[0036] Consider an example where the first material of the first layer is AlxGai-xN (wherein 0<x<l), and the second material of the second layer is AkGai-xN (wherein 0<x'<l and Ax').

[0037] If the second material of the second layer is AlGaN and the molar fraction of AIN is less than 0.5, the first material of the first layer is preferably GaN or AlGaN with a molar fraction of AIN less than 0.5.

[0038] If the second material of the second layer is AlGaN and the molar fraction of AIN is 0.5 or more, the first material of the first layer is preferably AIN or AlGaN with a molar fraction of AIN of 0.5 or more.

[0039] The first layer has one or more patterns that have the same shape as the crystal system of the first material in a plane parallel to a top of the surface of the first layer.

[0040] For example, if the first material of the first layer has a hexagonal crystal structure such as AlGaN, and the c-plane of the first material is parallel to the top surface of the first layer, then the shape of the patterns is a hexagon. On the other hand, if the first material of the first layer has a hexagonal crystal structure such as AlGaN, and the m-plane or a-plane of the first material is parallel to the top surface of the first layer, then the shape of the patterns is a rectangle. Also, if the first material of the first layer has a cubic crystal structure such as a diamond, then the shape of the patterns is a square.

[0041] The pattern can be a hole pattern having a desired shape, or a mask pattern formed of a mask material having a desired shape. In the case of a mask pattern, it is relatively easier to create larger patterns compared to a hole pattern, and having a larger pattern allows for a significant reduction in defect density. On the other hand, when using a mask pattern, it is necessary to select an appropriate material for forming the second layer that enables selective crystal growth in regions other than the mask. However, if a hole pattern is used, the selection of the mask material is not required. Additionally, in the case of a hole pattern, it is relatively easier to form voids within the crystal, and these voids can terminate defects, enabling a significant reduction in defect density. The hole patterns can be created by etching. The mask patterns can be created by depositing mask materials such as oxides, nitrides, fluorides, metals, etc.

[0042] The pattern may be a hole pattern fabricated by first forming a mask pattern using a mask material and then creating a hole pattern by growing crystal. When there is no suitable mask material for the material constituting the second layer, but a suitable mask material is available for the material constituting the first layer, this method may be employed. By using this method, it is possible to achieve a relatively large pattern and significantly reduce defects by forming voids.

[0043] If the pattern size is too large, it enables a significant reduction in defect density; however, it also increases the time for the crystals to coalesce during growth of the second layer, resulting in an increase in the amount of reaction gas used. On the other hand, if the pattern size is too small, the consumption of reaction gas and the time required for growth are reduced; however, it becomes difficult to create a uniform pattern with smaller sizes. Therefore, the length of one side of one of the patterns should preferably be 10 nm to 50000 nm, more preferably be 10 nm to 5000 nm, and even more preferably about 360 nm.

[0044] Each opposite side of the patterns of the first layer preferably should face each other to relieve the strain of the crystal of the second layer, namely, the patterns of the first layer are arranged such that one side of one of the patterns and an opposite side of another of the patterns face each other. For example, in the case of a hexagonal pattern, it is preferable that the patterns are arranged in a honeycomb shape.

[0045] If the distance between the patterns of the first layer is too large, some defects between the patterns may not bend and terminate, and may reach the top of the surface. On the other hand, if the distance is too small, the difficulty of processing the patterns increases and the uniformity of the patterns may deteriorate. For example, the distance should be 10 nm to 50000 nm, more preferably 100 nm to 5000 nm, and even more preferably about 320 nm.

[0046] If the pattern is a hole pattern, the holes are required to have a certain depth. If the holes are too shallow, strain relaxation and defect density reduction may not occur sufficiently. On the other hand, if the holes are too deep, it may become difficult to maintain the desired pattern shape.

[0047] If the pattern is a mask pattern, the mask is required to have a certain thickness. If the mask thickness is too thin, defect reduction may not occur sufficiently due to damage at high temperatures during crystal growth. On the other hand, if the thickness is too thick, it may take longer for lateral crystal growth, and pattern formation may become difficult.

[0048] Here, defining the depth of the hole pattern and the thickness of the mask pattern as the “pattern height,” the pattern height is in the range of 1 nm to 5000 nm, more preferably 50 nm to 1000 nm, and most preferably 100 nm or more.

[0049] A different elemental dopant may be added to the first layer. The addition of a dopant can increase the conductivity. The dopant material should be selected according to the material it is composed of. For example, Si or Mg is preferred for AlGaN.

[0050] Second Layer

[0051] The second material of the second layer has the same crystal system as the first layer but a different lattice constant.

[0052] For example, if the second material of the second layer is AlxGai-xN (wherein 0<x< 1), then:

[0053] AlxGai xN in the range of 0<x<0.3 is suitable as a substrate for creating UV-A devices and is thus preferable;

[0054] AlxGai-xN in the range of 0.2<x<0.5 is suitable as a substrate for creating UV- B devices and is thus preferable; and AlxGai -xN in the range of 0.5<x<l is suitable as a substrate for creating UV-C devices and is thus preferable.

[0055] A different elemental dopant may be added to the second layer. The addition of a dopant can increase the conductivity. The dopant material should be selected according to the material it is composed of. For example, Si or Mg is preferred for AlGaN.

[0056] Process Steps

[0057] Example 1

[0058] Figs. 1(a), 1(b), 1(c), 1(d), 1(e), 1(f), 1(g), 1(h), l(i) and l(j) are a process flow diagram that illustrates the experimental procedure for fabricating one embodiment of the present invention.

[0059] As a first step, a sapphire base substrate 101 was provided upon which GaN 102 was deposited, and then the GaN 102 on the sapphire base substrate 101 was cleaned using acetone, isopropanol, and pure water (Fig. 1(a)).

[0060] Instead of using sapphire, other substrates such as SiC, Si wafer, GaN, AIN can be used as the base substrate 101. For example, if a single crystal such as GaN is used, patterns can be made directly on the base substrate 101 and the base substrate 101 is used as both the base substrate 101 and the first layer 102.

[0061] The first layer 102 is not limited to GaN; it could be AIN. When the mole fraction of AIN in AlGaN, used as the second layer 106, is greater than 0.5, AIN is preferable due to its smaller lattice mismatch. Moreover, to further reduce the lattice mismatch with the second layer 105, the first material of the first layer 102 can be AlxGayIni-x-yN with a different composition from the second layer 106.

[0062] Subsequently, a SiCh hard mask 103 was deposited to a thickness of 70 nm using a Plasma Enhanced Chemical Vapor Deposition (PECVD) device (Fig. 1(b)). This hard mask 103 material is not limited to SiCh but can also be other materials such as oxides (TiCh, AI2O3, 1112O3, etc.), nitrides (SiNx, TiNx, etc.), metals (Ti, W, carbon, etc.), etc. The method of creating the hard mask 103 is not limited to PECVD; other methods such as sputtering or Atomic Layer Deposition (ALD) could also be used.

[0063] After cleaning the surface of the hard mask 103 again with acetone, isopropanol, and pure water, a positive-type photoresist 104 was applied (Fig. 1(c)), and a circular lithography pattern 105a was formed using a photolithography device (Fig. 1(d)). After forming the lithography pattern 105a, the circular pattern 105b shown in Fig. 1(g) was formed by etching the hard mask 103 using Inductively Coupled Plasma (ICP) device (Fig. 1(e)). Following this, the pattern 105c shown in Fig. 1(g) was formed by etching the first layer 102 using a Reactive Ion Etching (RIE) device (Fig. 1(1)). Then, after removing the photoresist using heated N-methyl-2- pyrrolidone (NMP) (Fig. 1(g)), wet etching was perfomied in an H3PO4 aqueous solution to change the pattern 105c of the first layer from a circular shape to a hexagonal shape (Fig. 1(h)). After the wet etching, the sample was rinsed with pure water and SiCL was removed using Hydrofluoric Acid (HF) (Fig. 1 (i)), resulting in the first layer 102 having a hexagonal pattern 105, resulting in a prepared GaN substrate 102 for use in subsequent processes.

[0064] The pattern 105a can be formed not only by photolithography but also by other methods, such as electron beam lithography, nanoimprint lithography, or soft lithography, among other suitable patterning techniques. The hexagonal pattern 105 can be directly created without going through the formation of the circular pattern. This makes etching to create the hexagonal pattern 105 unnecessary. Moreover, in the etching process, by adjusting the gas and power conditions and performing isotropic diy etching, the hexagonal pattern 105 can be created in the RIE process. Alternatively, wet etching could be performed directly without the use of RIE, thereby simplifying the process. For the wet etching of the first layer 102, instead of H3PO4, another acid such as H2SO4, or a base such as KOH, NaOH could be used. Wet etching conditions such as temperature and time can be changed depending on the material to be etched and the size and depth of the pattern 105b to be fabricated. The hexagonal patern 105 can be formed not only by etching the first layer 102 but also by using mask materials 103 like SiCh as illustrated in Fig. 2.

[0065] The base substrate 101 and first layer 102, which now comprises a prepared GaN substrate 102 with a hexagonal patern 105, was loaded into a Metal Organic Chemical Vapor Deposition (MOCVD) reactor and heated to over than 900 °C. A 2 pm thick layer of Al GaN 106 was then crystal-grown using Trimethylaluminium (TMA), Triethylgallium (TEG), and ammonia gas (NEE) (Fig. l(j)). The crystal grow th temperature in MOCVD can be anywhere between 500 °C and 1600 °C. The metalorganic precursors used can be another gas as long as Al or Ga is included in its gas molecule. The flow' rate of the organometallic gases of Al and Ga can be adjusted according to the desired composition of AIN in AlGaN. The gas flow' rate of ammonia can also be adjusted because a lower V / III ratio can yield more lateral cry stal growth. The second layer 106 may include voids. The presence of voids allows defects to be terminated at the locations where crystals grown from areas other than the hole patern merge.

[0066] As shown in Fig. 2, in w'hich sapphire was used as the base substrate 101, GaN as the first layer 102, and AlGaN as the second layer 106, the hexagonal patern 105 can be a hole patern formed by etching the first layer 102.

[0067] As shown in Fig. 3, the paterns 105 held by the first layer 102 may be formed by a mask 103 material, such as oxides, nitrides, fluorides, metals, etc.

[0068] As shown in Fig. 4, the paterns 105 held by the first layer 102 may be formed by depositing and processing a mask 103 material, and then creating a hole patern by crystal growing.

[0069] Fig. 5 is a SEM image of a prepared GaN substrate with a hexagonal patern 105 made by the method of Example 1. The side faces of the hexagonal paterns 105 are m-planes, and it is observed that the paterns 105 are arranged in a honeycomb configuration. The size of the fabricated patern 105 and the distance between paterns 105 can be observed and confirmed using SEM or optical microscopy. Additionally, the depth of the fabricated pattern 105 can be measured and confirmed using a surface profiler, such as a sty lus profiler, or by observing a cross-sectional SEM image.

[0070] Figs. 6(a) and 6(b) are the result of observing the surface of a substrate where AlGaN was grown on a substrate made by the method of Example 1 as shown in Fig. 6(a), and a prepared GaN substrate without a pattern as shown in Fig. 6(b), using an optical microscope. From the figures, it can be seen that the method of the present invention reduces cracks.

[0071] Figs. 7(a) and 7(b) show the cathodoluminescence results for AlGaN on patterned GaN on sapphire as shown in Fig. 7(a), and GaN on sapphire as shown in Fig. 7(b). The results show- that the defect density can be significantly reduced by the present invention.

[0072] Flowchart

[0073] Fig. 8 is a flowchart illustrating a method of suppressing cracks and reducing defect density by epitaxial growth of cry stals on a layer having a pattern of shapes based on a crystal system and having different lattice constants.

[0074] Block 801 represents the step of providing a base substrate.

[0075] Block 802 represents the step of forming a first layer comprised of a first material located on or above the base substrate.

[0076] Block 803 represents the step of forming one or more patterns in the first layer that have the same shape as a crystal system of the first material in a plane parallel to a top surface of the first layer.

[0077] Block 804 represents the step of epitaxially growing a second layer comprised of a second material located on or above the first layer, wherein the second material of the second layer has the cry stal system of the first material but a different lattice constant.

[0078] Block 805 represents the end result of the steps, namely, a crack-free and low - dislocation crystal grown on a patterned substrate, obtained by the method. In one embodiment, the end result is crack-free AlGaN with low defect density formed on GaN or AIN substrates. The crack-free and low-dislocation crystal grown on a patterned substrate may be used for various optoelectronic devices, such as a lightemitting device, a laser diode, a power device, a radio frequency (RF) device, as well as other devices.

[0079] This invention may include the following alternatives:

[0080] • The base substrate may be selected from III-V group materials (such as InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs. AlAs, or alloys of III group and V group elements), VI group materials (such as Si, SiGe. SiC, C. or alloys of VI group elements), oxide materials (such as SiCh, AI2O3, TiCh, ZnO, (In, Ga)2Ch), or sapphire. Since any material can be used for the base substrate, a low-cost substrate can be selected.

[0081] • The first material of the first layer may be selected from III-V group materials (such as InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs, AlAs, or alloys of III group and V group elements), VI group materials (such as Si, SiC, C, or alloys of VI group elements), or oxide materials (such as SiCh, AI2O3, TiCh, ZnO, (In, Ga)2O3), or sapphire. This method can be applied to other material systems.

[0082] • The second material of the second layer may be comprised of a different chemical composition containing at least one or more elements of the first material of the first layer.

[0083] • The chemical composition of the second material of the second layer may change in a gradient manner in a depth direction.

[0084] • The first material of the first layer may comprise AlxGai-xN wherein 0<x<l, and the second material of the second layer may comprise Alx'Gai-x wherein 0<x'<l and x= x'.

[0085] • The first material of the first layer may comprise InxGai-xN wherein 0<x<l, and the second material of the second layer may comprise InxGai-x wherein 0<x'<l and x= x'. • The first and second materials of the first and second layers may include other elements as dopants with a doping level is 1 X IO10cm'3or more and 1 X 1022cm'3or less.

[0086] • The mask used to pattern the first layer may be comprised of a material selected from an oxide, a nitride, a fluoride, or a metal element.

[0087] • The patterns of the first layer may be arranged such that one side of one of the patterns and an opposite side of another of the patterns face each other.

[0088] • The pattern height of the first layer may be 10 nm or more and 5000 nm or less.

[0089] • The length of one side of the patterns of the first layer may be 10 nm or more and 50000 nm or less.

[0090] • The length of one side of the patterns of the first layer may be 10 nm or more and 5000 nm or less.

[0091] • The distance between the patterns of the first layer may be 10 nm or more and 50000 nm or less.

[0092] • The distance between the patterns of the first layer may be 10 nm or more and 5000 nm or less.

[0093] References

[0094] The following publications are incorporated by reference herein:

[0095] 1. H. Miyake, N. Matsuda, Y. Ogawahara, M. Narukawa, K. Hiramatsu, T. Ezaki, N. Kuwano, J. Cryst. Growth. 2008, 310, 4885-4887.

[0096] 2. J. Wang, N. Xie, F. Xu, L. Zhang, J. Lang, X. Kang, Z. Qin, X. Yang, N. Tang, X. Wang, W. Ge. B. Shen, Nat. Mater. 2023, 22. 853-859.

[0097] Conclusion

[0098] This concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A structure, comprising: a base substrate; a first layer comprised of a first material located on or above the base substrate; and an epitaxially grown second layer comprised of a second material located on or above the first layer; wherein:(a) the first layer has one or more patterns that have the same shape as a cry stal system of the first material in a plane parallel to a top surface of the first layer; and(b) the second material of the second layer has the crystal system of the first material but a different lattice constant.

2. The structure of claim 1, wherein the base substrate is selected from III-V group materials (such as InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs. AlAs, or alloys of III group and V group elements), VI group materials (such as Si, SiGe, SiC, C, or alloys of VI group elements), oxide materials (such as S1O2. AI2O3, TiCh, ZnO, (In, Ga)2Ch), or sapphire.

3. The structure of claim 1, wherein the first material of the first layer is selected from III-V group materials (such as InN, GaN, AIN, InP, GaP, A1P, InAs, GaAs, AlAs, or alloys of III group and V group elements), VI group materials (such as Si, SiC, C, or alloys of VI group elements), or oxide materials (such as SiCh, AI2O3. T1O2. ZnO. (In. Ga)2Os). or sapphire.

4. The structure of claim 1, wherein the patterns of the first layer are either etched or masks formed from a material selected from an oxide, a nitride, a fluoride, or a metal element.

5. The structure of claim 1 , wherein the patterns of the first layer are arranged such that one side of one of the patterns and an opposite side of another of the patterns face each other.

6. The structure of claim 1, wherein a pattern height of the first layer is 10 nm or more and 5000 nm or less.

7. The structure of claim 1, wherein a length of one side of the patterns of the first layer is 10 nm or more and 50000 nm or less.

8. The structure of claim 7, wherein a length of one side of the patterns of the first layer is 10 nm or more and 5000 nm or less.

9. The structure of claim 1, wherein a distance between the patterns of the first layer is 10 nm or more and 50000 nm or less.

10. The structure of claim 9, wherein a distance between the patterns of the first layer is 10 nm or more and 5000 nm or less.

11. The structure of claim 1 , wherein the second material of the second layer is comprised of a different chemical composition containing at least one or more elements of the first material of the first layer.

12. The structure of claim 1, wherein the chemical composition of the second material of the second layer changes in a gradient manner in a depth direction.

13. The structure of claim 1, wherein the first material of the first layer is AlxGai-xN wherein 0<x<l, and the second material of the second layer is Alx’Gai-x'N wherein 0<x'<l and x Ax'.

14. The structure of claim 1, wherein the first material of the first layer is InxGai-xN wherein 0<x<l, and the second material of the second layer is InX’Gai-X'N wherein 0<x'< 1 and x Ax'.

15. The structure of claim 1, wherein the first and second materials of the first and second layers include other elements as dopant and a doping level is 1 X IO10cm’3or more and 1 X 1022cm’3or less.

16. A light-emitting device comprising the structure of claim 1.

17. A laser diode comprising the structure of claim 1.

18. A power device comprising the structure of claim 1.

19. A radio frequency (RF) device comprising the structure of claim 1.

20. A method, comprising: providing a base substrate; forming a first layer comprised of a first material located on or above the base substrate; and epitaxially growing a second layer comprised of a second material located on or above the first layer; wherein:(a) the first layer has one or more patterns that have the same shape as a cry stal system of the first material in a plane parallel to a top surface of the first layer; and(b) the second material of the second layer has the crystal system of the first material but a different lattice constant.

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