High-quality gallium nitride crystals, their flux growth method and applications

Abstract

The present invention discloses a high-quality gallium nitride crystal, a flux growth method thereof and applications. The growth method includes: performing primary growth using a first flux system to obtain an intermediate crystal, forming a plurality of gallium nitride nanowires on the growth surface of the intermediate crystal to form a nanowire template layer, and the first flux system contains metallic nickel; using a second flux system, and performing secondary growth with the intermediate crystal as a basis to form a merged growth layer that grows outward and merges from the nanowire template layer, and finally obtaining a high-quality gallium nitride crystal. The present invention uses a two-step flux method to achieve crystal growth. During the first growth, gallium nitride nanowires are formed by the catalytic action of metallic nickel. The nanowire template layer composed of the gallium nitride nanowires has the characteristics of being dense and uniform. The gallium nitride crystal obtained by performing secondary growth based on the nanowire template layer grows uniformly, more effectively reducing the dislocation density of the regrown gallium nitride and reducing stress at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of gallium nitride semiconductors, and in particular, to a high-quality gallium nitride crystal, a flux growth method thereof, and an application thereof. Background Art

[0002] Gallium nitride-based devices are widely used in solid-state lighting, lasers, and high-power devices. With the increasing requirements for performance parameters, high-quality gallium nitride substrates are an important way to achieve high-performance devices. A gallium nitride substrate with a low dislocation density and low curvature can effectively reduce problems such as dislocation leakage and stress concentration in gallium nitride-based devices.

[0003] The flux method is an important single-crystal substrate growth technology. Using a two-step growth method, first, a high-density nanowire array is grown on a substrate by the flux method, and further, a gallium nitride bulk single crystal with low dislocations and low stress is grown on the nanowire array template by the flux method, which can effectively improve the crystal quality and promote the development of high-performance gallium nitride-based devices.

[0004] However, the current technical solutions for growing gallium nitride crystals by the two-step method still have some problems, mainly reflected in the insufficient process controllability of the nanowire array template, resulting in poor uniformity of the nanowires on the plane, and ultimately leading to a decline in the quality of the obtained crystals. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a high-quality gallium nitride crystal, a flux growth method thereof, and an application thereof.

[0006] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0007] In a first aspect, the present invention provides a flux growth method for a high-quality gallium nitride crystal, which includes:

[0008] Using a first flux system, performing a first growth based on an original substrate to obtain an intermediate crystal, and forming a plurality of gallium nitride nanowires on the growth surface of the intermediate crystal to form a nanowire template layer, wherein the surface material of the original substrate is gallium nitride, and the first flux system contains metallic nickel;

[0009] Using a second flux system, performing a second growth based on the intermediate crystal to form a merged growth layer that grows outward and merges from the nanowire template layer, and finally obtaining a high-quality gallium nitride crystal.

[0010] In a second aspect, the present invention further provides a high-quality gallium nitride crystal obtained by the above flux growth method, which includes an original substrate, a nanowire template layer, and a merged growth layer that are sequentially stacked in the thickness direction;

[0011] Among them, the dislocation density of the combined growth layer is 10 3 cm -2 or less.

[0012] Thirdly, the present invention also provides the application of the above high-quality gallium nitride crystal in the fields of solid-state lighting, lasers, and high-power electrical devices.

[0013] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0014] The technical solution provided by the present invention uses a two-step flux method to achieve crystal growth. During the first growth, gallium nitride nanowires are formed by the catalytic action of metallic nickel. The nanowire template layer composed of the gallium nitride nanowires has the characteristics of being dense and uniform. The gallium nitride crystal obtained by secondary growth based on the nanowire template layer grows uniformly, more effectively reducing the dislocation density of the regrown gallium nitride and reducing stress at the same time.

[0015] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it in accordance with the content of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic flow chart of a flux growth method provided by a typical embodiment of the present invention;

[0017] Figure 2 is a schematic principle diagram of a flux growth method provided by a typical embodiment of the present invention;

[0018] Figure 3 is a SEM photograph of the cross-section and surface morphology of a nanowire template layer formed by a flux growth method provided by a typical embodiment of the present invention;

[0019] Figure 4 is a SEM photograph of the cross-section morphology of a high-quality gallium nitride crystal obtained by a flux growth method provided by a typical embodiment of the present invention;

[0020] Figure 5 is a transmission electron image of a high-quality gallium nitride crystal obtained by a flux growth method provided by a typical embodiment of the present invention under one diffraction condition;

[0021] Figure 6 is a transmission electron image of a high-quality gallium nitride crystal obtained by a flux growth method provided by a typical embodiment of the present invention under another diffraction condition. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Currently, the conventional flux method for growing gallium nitride generally directly uses a HVPE gallium nitride seed crystal or a gallium nitride template substrate coated on sapphire for a single growth. During the growth process, the dislocation density is affected by the substrate, making it difficult to reduce the dislocation density. At the same time, the stress state is also affected by the substrate effect, and cracking may occur in extreme cases.

[0023] As shown in the above background technology, in order to improve the problems of the above conventional growth methods, a large number of existing technologies have tried to grow high-quality gallium nitride crystals. For example:

[0024] (1) Chinese invention patent with publication number CN111434811A: Self-separated gallium nitride single crystal and its flux method growth method, which discloses a method for growing self-separated gallium nitride single crystal by the flux method, including: using the flux method, using self-supporting gallium nitride as a seed crystal, growing a microporous layer on the self-supporting gallium nitride; and using the liquid phase epitaxy method to grow a self-separated gallium nitride single crystal on the microporous layer.

[0025] (2) An existing article (IMADE M, IMANISHI M, TODOROKI Y, et al. Fabrication of low-curvature 2 in. GaN wafers by Na-flux coalescence growth technique[J]. Appl Phys Express, 2014, 7(3).) reported a method of using metal organic chemical vapor deposition to mask a layer of gallium nitride multi-point seeds on a sapphire substrate, and then growing gallium nitride by the flux method. The lateral coalescence growth on the gallium nitride multi-point seeds is used to reduce dislocations and curvature.

[0026] (3) An existing article (Nanowire-Templated Lateral Epitaxial Growth of Low-Dislocation Density Nonpolar a-Plane GaN on r-Plane Sapphire. Adv Mater, 2009, 21(23): 2416-20.) reported a method of first growing a layer of nanowire template on a sapphire substrate, and then laterally growing and merging gallium nitride on the gallium nitride nanowire template to finally obtain a gallium nitride thick film with a low dislocation density.

[0027] (4)Chinese invention patent with publication number CN103387213A: A gallium nitride nanowire and its preparation method, which discloses a gallium nitride nanowire and its preparation method, including: under normal pressure, chemically vapor depositing GaN nanowires on a substrate loaded with a catalyst for preparing gallium nitride nanowires by using elemental gallium, gallium oxide and a gas containing ammonia.

[0028] (5)Chinese invention patent with publication number CN103774230A: A method for preparing gallium nitride nanowires without ammonia, which discloses a method for preparing gallium nitride nanowires without ammonia. Mix gallium oxide powder and carbon powder, grind for more than 2 minutes to obtain a precursor powder; deposit a metal catalyst film with a thickness of 5 nm - 30 nm on a substrate that has been cleaned, treated with hydrofluoric acid and dried; put the precursor powder and the substrate into a plasma-enhanced chemical vapor deposition system to prepare gallium nitride nanowires.

[0029] (6)Chinese invention patent with publication number CN104313548A: A method for preparing gallium nitride nanowires, which discloses a method for preparing gallium nitride nanowires by reacting ammonia with potassium oxide using nickel or gold on a silicon substrate.

[0030] (7)Chinese invention patent with publication number CN104966666A: A method for fabricating nitride nanowires, which discloses a method for catalytically growing gallium nitride nanowires using a mask template.

[0031] (8)Chinese invention patent with publication number CN113488433A: Funnel-shaped gallium nitride nanowires and their preparation method, which discloses a funnel-shaped gallium nitride nanowires and their preparation method.

[0032] (9)Chinese invention patent with publication number CN111434811A: Self-separating gallium nitride single crystal and its growth method by flux method, which adopts a two-step growth mode, first forming a microporous layer, and then forming a crystal layer.

[0033] The above-mentioned prior arts can be roughly divided into two categories. One category catalytically grows gallium nitride nanowires and then performs secondary growth. The morphology of the grown nanowires is poorly controlled and the growth orientations are inconsistent, which is not conducive to using the nanowires as a template for subsequent nanowire growth. Among them, some technical solutions disclose the use of a template to catalytically grow a gallium nitride nanowire array. Although the orientation consistency is better, the process is complex and the cost of the nanowire template is increased. That is, the defect of this type of prior art is that it is difficult to obtain high-density and uniform nanowires at a low cost or with relatively simple process steps.

[0034] Another category of prior arts first manufactures micropores and then grows gallium nitride by the flux method. This method cannot control the uniformity of the micropores on the substrate, and the grown gallium nitride may have uneven dislocation density distribution.

[0035] In view of the deficiencies in the prior art, through long-term research and a large number of practices, the inventors of this case have been able to propose the technical solution of the present invention. The following will further explain the technical solution, its implementation process, principles, etc.

[0036] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0037] Moreover, relational terms such as "first" and "second" are only used to distinguish one component or method step with the same name from another, and do not necessarily require or imply any actual relationship or order between these components or method steps.

[0038] See Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a flux growth method for high-quality gallium nitride crystals, which includes the following steps:

[0039] Adopt a first flux system to perform primary growth based on the original substrate to obtain an intermediate crystal. A plurality of gallium nitride nanowires are formed on the growth surface of the intermediate crystal to form a nanowire template layer. Among them, the surface material of the original substrate is gallium nitride, and the first flux system contains metallic nickel;

[0040] Adopt a second flux system to perform secondary growth based on the intermediate crystal to form a merged growth layer that grows outward and merges from the nanowire template layer, and finally obtain high-quality gallium nitride crystals.

[0041] The present invention is based on the flux method for growing gallium nitride. It ingeniously adopts a two-step method. First, a low-stress and dislocation-free gallium nitride nanowire template is grown by the flux method. On this basis, a single crystal of gallium nitride is grown by the flux method. This not only reduces the process complexity and cost, but also reduces the dislocation density and stress, and improves the growth quality.

[0042] In addition, compared with the above-mentioned first type of prior art, the technical solution provided by the embodiment of the present invention directly catalyzes the growth of gallium nitride nanowires by using a flux device, without the need for a mask, with low process complexity, and through a nanowire growth method completely different from the above-mentioned prior art, the obtained nanowires have high orientation and uniformity, low stress and no dislocations. Compared with the above-mentioned second type of technical solution, the nanowires prepared in the first step of the present invention are dislocation-free and grow uniformly, more effectively reducing the dislocation density of the regrown gallium nitride and reducing the stress at the same time.

[0043] Regarding specific implementation details, in some embodiments, the first flux system is a Ga-Na system.

[0044] In some embodiments, the mass fraction of metallic nickel in the first flux system is 0.5% to 2.5%.

[0045] In some embodiments, the temperature for the primary growth is 750 to 850 °C, the nitrogen pressure is 2 to 4 MPa, and the growth time is 5 to 10 h.

[0046] In some embodiments, the height of the gallium nitride nanowires is 1 to 3 μm.

[0047] In some embodiments, the areal density of the gallium nitride nanowires is 10 7 cm -2 or more, that is, the number of gallium nitride nanowires per square centimeter is 10 7 or more.

[0048] In some embodiments, the temperature for the secondary growth is 600 to 850 °C, the nitrogen pressure is 2 to 5 MPa, and the growth time is 10 - 100 h.

[0049] In some embodiments, the original substrate includes a gallium nitride seed crystal or a hetero-substrate having a gallium nitride layer on its surface.

[0050] In some embodiments, when the original substrate uses a hetero-substrate, the thickness of the gallium nitride layer is 3 to 5 μm.

[0051] As some typical examples of the above technical solutions, some representative implementation cases of the present invention selected HVPE gallium nitride seeds and used a two-step growth method to grow high-quality gallium nitride single crystals.

[0052] First step: Using metallic nickel as a catalyst, add it to the gallium-sodium raw material according to a mass fraction of 0.5% to 2.5%, at a temperature of 750 to 850 °C, a nitrogen pressure of 2 to 4 MPa, and grow for 5 to 10 h to obtain a high-density gallium nitride array with a height of 1 to 3 μm. After the growth is completed, clean the growth with absolute ethanol and water.

[0053] Second step: Re-grow the substrate with the obtained nanowire template layer using the flux method. The growth system uses the currently mature gallium-sodium melt, at a temperature of 600 to 850 °C, a nitrogen pressure of 2 to 5 MPa, and grow for 10 - 100 h.

[0054] After experiments and tests under various conditions, it is found that the gallium nitride single crystals grown by the above process have almost no stress and the dislocation density is lower than 10 3 cm -2 .

[0055] The principle of achieving the above technical effects lies in:

[0056] High-quality gallium nitride single crystals are grown by a two-step method. First, nickel metal is used as a catalyst, and the flux method is used to form a nano-scale catalyst in the melt to catalytically grow a high-density, dislocation-free gallium nitride nanowire array template. Then, the gallium nitride nanowire template is used as a substrate, and high-quality gallium nitride single crystals are continuously grown by the traditional flux method (gallium-sodium system). Since the gallium nitride grown in the second growth is grown on the nanowires, the spacing between the nanowires will promote the lateral merging of the growth layer, causing the dislocations to bend and annihilate under the radial force, while leaving voids to release stress. Therefore, the grown gallium nitride has the characteristics of low dislocation density and low stress.

[0057] Corresponding to the above growth process, the second aspect of the embodiments of the present invention also provides high-quality gallium nitride crystals obtained by the flux growth method provided in any of the above embodiments, which includes a raw substrate, a nanowire template layer, and a merged growth layer stacked in sequence along the thickness direction; wherein, the dislocation density of the merged growth layer is within 10 3 cm -2 or less.

[0058] In addition, the third aspect of the embodiments of the present invention also provides the application of the high-quality gallium nitride crystals provided in any of the above embodiments in the fields of solid-state lighting, lasers, and high-power electrical devices.

[0059] The technical solution of the present invention will be further described in detail below through several embodiments in combination with the drawings. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0060] Example 1

[0061] In this example, an HVPE gallium nitride seed crystal is selected, and high-quality gallium nitride single crystals are grown by a two-step growth method.

[0062] First step: Nickel metal is used as a catalyst and added to the raw material with a sodium-gallium molar ratio of 30:70 at a molar fraction of 1.5%. The temperature is 800 °C, the nitrogen pressure is 3 MPa, and the growth is carried out for 7.5 h to obtain a high-density gallium nitride array with a height of 2 μm. After the growth is completed, it is washed clean with anhydrous ethanol and water. The cross-section and surface morphology of the obtained product are as shown in the Figure 3 tilted-field electron microscope photograph shown, and it can be seen that the gallium nitride nanowires formed in this way are extremely uniformly distributed and densely arranged on the surface.

[0063] Second step: The substrate with the nanowire template obtained is grown again using the flux method. The growth system uses the currently mature gallium-sodium melt, the temperature is 750 °C, the nitrogen pressure is 3.5 MPa, and the growth is carried out for 50 h. The growth result is as shown in Figure 4As shown

[0064] After testing, the grown gallium nitride single crystal has almost no stress, and the dislocation density is lower than 10 3 cm -2 .

[0065] Example 2

[0066] This example is generally the same as Example 1, except that the substrate is replaced with a sapphire substrate with a 3 - 5 μm thick gallium nitride template on its surface. The grown gallium nitride single crystal has a lower compressive stress, and the dislocation density is lower than 10 3 cm -2 .

[0067] Example 3

[0068] This example is generally the same as Example 1, except that the specific parameter conditions are different:

[0069] In the first step, the addition amount of metallic nickel is adjusted to 0.5%, the temperature is 850 °C, the nitrogen pressure is 4 MPa, and the growth time is 5 h;

[0070] In the second step, the temperature is 600 °C, the nitrogen pressure is 2 MPa, and the growth time is 10 h.

[0071] Example 4

[0072] This example is generally the same as Example 1, except that the specific parameter conditions are different:

[0073] In the first step, the addition amount of metallic nickel is adjusted to 2.5%, the temperature is 750 °C, the nitrogen pressure is 2 MPa, and the growth time is 10 h;

[0074] In the second step, the temperature is 850 °C, the nitrogen pressure is 5 MPa, and the growth time is 100 h.

[0075] Comparative Example 1

[0076] This example is generally the same as Example 1, except that the first - step growth in the two - step method is not carried out, and the substrate is directly subjected to the second - step growth. The grown gallium nitride has a large stress, is significantly affected by the substrate, and the dislocation density is greater than 10 5 cm -2 .

[0077] Comparative Example 2

[0078] This example is generally the same as Comparative Example 1, except that similar to Example 2, the substrate is replaced with a sapphire substrate with a 3 - 5 μm thick gallium nitride template on its surface. The grown gallium nitride has a large stress, cracks appear, and the dislocation density is greater than 10 6 cm -2 .

[0079] Comparative Example 3

[0080] This example is generally the same as Comparative Example 1, except that only the first-step growth of the nanowire array is carried out. The obtained gallium nitride nanowires are dislocation-free. The results are shown in the Figure 5 and Figure 6 transmission electron double-beam diffraction images under different conditions shown.

[0081] Comparative Example 4

[0082] This example is generally the same as Comparative Example 1, except that the nanowire array in the first step is changed to an artificial cavity layer prepared by pre-corroding the seed crystal with a sodium hydroxide-potassium hydroxide solution, and then the second-step bulk single crystal growth is directly carried out. The growth result shows that the dislocation density is greater than 10 5 cm -2 .

[0083] Comparative Example 5

[0084] This example is generally the same as Comparative Example 1, except that the nanowire array in the first step is changed to grow a microporous layer under the conditions of a pressure of 5 MPa and a temperature of 700 °C. The diameter of the microporous layer is 5 μm and the thickness is 30 μm. Then the second-step bulk single crystal growth is directly carried out. The growth result shows that the microporous layer is prone to increase the probability of inclusions, affecting the growth quality. The dislocation density in some local areas is greater than 10 7 cm -2 , and the dislocation density in some areas is less than 10 5 cm -2 .

[0085] In addition, the inventors of the present invention repeated various prior art technical solutions of first forming nanowires and then performing combined growth during the technology research and development process. However, these technical solutions all have problems of uneven distribution of gallium nitride nanowires and insufficient areal density. The quality of the finally formed gallium nitride crystals is inferior to that of the crystals obtained in the representative embodiments of the present invention.

[0086] Based on the above embodiments and comparative examples, it can be clearly seen that the technical solution provided by the embodiments of the present invention uses a two-step flux method to achieve crystal growth. During the first growth, gallium nitride nanowires are formed by the catalytic action of metallic nickel. The nanowire template layer composed of the gallium nitride nanowires has the characteristics of being dense and uniform. The gallium nitride crystals obtained by secondary growth based on this nanowire template layer grow uniformly, more effectively reducing the dislocation density of the regenerated gallium nitride and at the same time reducing the stress.

[0087] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A flux growth method for high-quality gallium nitride crystals, characterized in that, Comprising: Using a first flux system, a primary growth is carried out based on the original substrate to obtain an intermediate crystal. A plurality of gallium nitride nanowires with dense and uniformly arranged surfaces are formed on the growth surface of the intermediate crystal, constituting a nanowire template layer. Among them, the surface material of the original substrate is gallium nitride, the first flux system contains metallic nickel, the first flux system is a Ga-Na system, the mass fraction of metallic nickel in the first flux system is 0.5 to 2.5%, the temperature of the primary growth is 750 to 850 °C, the nitrogen pressure is 2 to 4 MPa, the growth time is 5 to 10 h, and the areal density of the gallium nitride nanowires is 10 7 cm -2 or more; Adopting a second flux system, secondary growth is carried out based on the intermediate crystal to form a merged growth layer that grows outward and merges from the nanowire template layer, and finally a high-quality gallium nitride crystal is obtained.

2. The flux growth method according to claim 1, wherein, The height of the gallium nitride nanowires is 1 to 3 μm.

3. The flux growth method according to claim 1, characterized in that, The temperature of the secondary growth is 600 to 850 °C, the nitrogen pressure is 2 to 5 MPa, and the growth time is 10 - 100 h.

4. The flux growth method according to claim 1, wherein, The original substrate includes a gallium nitride seed crystal or a hetero-substrate with a gallium nitride layer on its surface.

5. The flux growth method according to claim 4, wherein When the original substrate uses a hetero-substrate, the thickness of the gallium nitride layer is 3 to 5 μm.

6. The high-quality gallium nitride crystal obtained by the flux growth method according to any one of claims 1-5, characterized in that Including an original substrate, a nanowire template layer, and a merged growth layer that are sequentially stacked along the thickness direction; Among them, the dislocation density of the merged growth layer is 10 3 cm -2 or less.

7. Application of the high-quality gallium nitride crystal according to claim 6 in the fields of solid-state lighting, lasers, and high-power electrical devices.

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