High-quality gallium nitride crystal and fluxing agent growth method and application thereof

Abstract

The invention discloses a high-quality gallium nitride crystal and a fluxing agent growth method and application thereof. The growth method comprises the steps that a first fluxing agent system is adopted for primary growth to obtain an intermediate crystal, a plurality of gallium nitride nanowires are formed on the growth face of the intermediate crystal to form a nanowire template layer, and the first fluxing agent system contains metal nickel; a second fluxing agent system is adopted, secondary growth is carried out on the basis of the middle crystal, a combined growth layer which grows outwards in a combined mode from the nanowire template layer is formed, and finally the high-quality gallium nitride crystal is obtained. According to the method, the crystal growth is realized by adopting a two-step fluxing agent method, the gallium nitride nanowires are formed by utilizing the catalytic action of metal nickel during the first growth, the nanowire template layer formed by the gallium nitride nanowires has the characteristics of compactness and uniformity, and the gallium nitride crystal obtained by carrying out the secondary growth based on the nanowire template layer is uniform in growth and high in yield. The dislocation density of regrown gallium nitride is reduced more effectively, and the stress is reduced at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of gallium nitride semiconductors, and particularly 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 technique. 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: In the first aspect, the present invention provides a flux growth method for a high-quality gallium nitride crystal, which includes: Using a first flux system, performing primary 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; Using a second flux system, performing 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 obtaining a high-quality gallium nitride crystal.

[0007] In the 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; Among them, the dislocation density of the merged growth layer is below 10 3 cm -2 hereinafter.

[0008] In a third aspect, the present invention also provides the application of the above high-quality gallium nitride crystals in the fields of solid-state lighting, lasers, and high-power electrical devices.

[0009] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include: 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 crystals obtained by secondary growth based on this nanowire template layer grow uniformly, more effectively reducing the dislocation density of the regrown gallium nitride and simultaneously reducing the stress.

[0010] 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 takes the preferred embodiments of the present invention and combines detailed drawings for illustration as follows. Description of the Drawings

[0011] Figure 1 is a schematic flow chart of a flux growth method provided by a typical embodiment of the present invention; Figure 2 is a schematic principle diagram of a flux growth method provided by a typical embodiment of the present invention; Figure 3 is a SEM photograph of the cross-section and surface morphology of the nanowire template layer formed by a flux growth method provided by a typical embodiment of the present invention; Figure 4 is a SEM photograph of the cross-sectional morphology of high-quality gallium nitride crystals obtained by a flux growth method provided by a typical embodiment of the present invention; Figure 5 is a transmission electron image of high-quality gallium nitride crystals obtained by a flux growth method provided by a typical embodiment of the present invention under one diffraction condition; Figure 6 is a transmission electron image of high-quality gallium nitride crystals obtained by a flux growth method provided by a typical embodiment of the present invention under another diffraction condition. Detailed Embodiments

[0012] Currently, the conventional flux method for gallium nitride growth generally directly uses HVPE gallium nitride seeds or a gallium nitride template substrate plated on sapphire for primary growth. The dislocation density during the growth process 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 in extreme cases, cracking will occur.

[0013] As shown in the background art above, in order to improve the problems of the above-mentioned conventional growth methods, a great deal of existing technologies have attempted to grow high-quality gallium nitride crystals. For example: (1) Chinese invention patent with publication number CN111434811A: Self-separating gallium nitride single crystal and its flux method growth method, discloses a method for growing self-separating gallium nitride single crystal by the flux method, including: using the flux method, taking 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-separating gallium nitride single crystal on the microporous layer.

[0014] (2) An existing article (IMADE M, IMANISHI M, TODOROKI Y, et al. Fabricationof 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.

[0015] (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 low dislocation density gallium nitride thick film.

[0016] (4) Chinese invention patent with publication number CN103387213A: A gallium nitride nanowire and its preparation method, 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.

[0017] (5)Chinese invention patent with publication number CN103774230A: A method for preparing gallium nitride nanowires without ammoniation, which discloses a method for preparing gallium nitride nanowires without ammoniation. Gallium oxide powder is mixed with carbon powder and ground for more than 2 minutes to obtain a precursor powder; a metal catalyst film with a thickness of 5 nm - 30 nm is deposited on a substrate that has been cleaned, treated with hydrofluoric acid, and dried; the precursor powder and the substrate are placed in a plasma-enhanced chemical vapor deposition system to prepare gallium nitride nanowires.

[0018] (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 gas with potassium oxide using nickel or gold on a silicon substrate.

[0019] (7)Chinese invention patent with publication number CN104966666A: A method for fabricating nitride nanowires, which discloses a method for catalytic growth of gallium nitride nanowires using a mask template.

[0020] (8)Chinese invention patent with publication number CN113488433A: Funnel-shaped gallium nitride nanowires and a preparation method thereof, which discloses a funnel-shaped gallium nitride nanowires and a preparation method thereof.

[0021] (9)Chinese invention patent with publication number CN111434811A: Self-separating gallium nitride single crystal and a flux method for growing the same, which adopts a two-step growth mode, first forming a microporous layer, and then forming a crystal layer.

[0022] The above-mentioned prior arts can be roughly divided into two categories. One category is to catalytically grow gallium nitride nanowires and then perform secondary growth. The morphology control of the grown nanowires is poor, and the growth orientations are inconsistent, which is not conducive to subsequent nanowire growth as a nanowire template. 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, increasing the cost of the nanowire template. 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.

[0023] Another category of prior art uses a method of first creating micropores and then growing gallium nitride by the flux method. This method cannot control the uniformity of the micropores on the substrate, and the dislocation density distribution of the grown gallium nitride may be uneven.

[0024] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention through long-term research and a large number of practices. The following will further explain the technical solution, its implementation process, principle, etc.

[0025] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those described herein. Therefore, the scope of the present invention is not limited by the specific embodiments disclosed below.

[0026] 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 such actual relationship or order between these components or method steps.

[0027] 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: 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 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, and the first flux system contains metallic nickel; Using a second flux system, a 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.

[0028] 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.

[0029] 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 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.

[0030] Regarding specific implementation details, in some embodiments, the first flux system is a Ga-Na system.

[0031] In some embodiments, the mass fraction of metallic nickel in the first flux system is 0.5 - 2.5%.

[0032] In some embodiments, the temperature of the primary growth is 750 - 850 °C, the nitrogen pressure is 2 - 4 MPa, and the growth time is 5 - 10 h.

[0033] In some embodiments, the height of the gallium nitride nanowires is 1 - 3 μm.

[0034] In some embodiments, the areal density of the gallium nitride nanowires is above 10 7 cm -2 , that is, the number of gallium nitride nanowires per square centimeter is above 10 7 roots.

[0035] In some embodiments, the temperature of the secondary growth is 600 - 850 °C, the nitrogen pressure is 2 - 5 MPa, and the growth time is 10 - 100 h.

[0036] In some embodiments, the original substrate includes a gallium nitride seed crystal or a hetero-substrate with a gallium nitride layer on its surface.

[0037] In some embodiments, when the original substrate uses a hetero-substrate, the thickness of the gallium nitride layer is 3 - 5 μm.

[0038] As some typical examples of the above technical solutions, some representative implementation cases of the present invention select HVPE gallium nitride seed crystals and grow high-quality gallium nitride single crystals by a two-step growth method.

[0039] First step: Add metallic nickel as a catalyst to the gallium-sodium raw material according to a mass fraction of 0.5% - 2.5%, at a temperature of 750 - 850 °C, a nitrogen pressure of 2 - 4 MPa, and grow for 5 - 10 h to obtain a high-density gallium nitride array with a height of 1 - 3 μm. After the growth is completed, clean the growth with absolute ethanol and water.

[0040] Second step: Re-grow the substrate with the nanowire template layer obtained above by the flux method. The growth system uses the currently mature gallium-sodium melt, at a temperature of 600 - 850 °C, a nitrogen pressure of 2 - 5 MPa, and grow for 10 - 100 h.

[0041] Through 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 .

[0042] The principle of achieving the above technical effects lies in: High-quality gallium nitride single crystals are grown by a two-step method. First, nickel metal is used as a catalyst, and a flux method is adopted to form a nanoscale 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 stage grows on the nanowires, the spacing between the nanowires promotes the lateral merging of the growth layer, causing the dislocations to bend and annihilate under the radial force, and at the same time leaving voids to release stress. Therefore, the grown gallium nitride has the characteristics of low dislocation density and low stress.

[0043] 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.

[0044] 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.

[0045] The technical solutions of the present invention are further described in detail below through several embodiments in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0046] Example 1 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.

[0047] 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 absolute 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, and it can be seen that the gallium nitride nanowires formed in this way are extremely uniformly distributed and densely arranged on the surface.

[0048] 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 the Figure 4 figure.

[0049] After testing, the grown gallium nitride single crystal has almost no stress, and the dislocation density is lower than 103 cm -2 。

[0050] Example 2 This example is generally the same as Example 1, except that the substrate is replaced with a sapphire substrate having a 3 - 5 μm thick gallium nitride template on its surface. The grown gallium nitride single crystal has a relatively low compressive stress, and the dislocation density is less than 10 3 cm -2 。

[0051] Example 3 This example is generally the same as Example 1, except that the specific parameter conditions are different: 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; In the second step, the temperature is 600 °C, the nitrogen pressure is 2 MPa, and the growth time is 10 h.

[0052] Example 4 This example is generally the same as Example 1, except that the specific parameter conditions are different: 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; In the second step, the temperature is 850 °C, the nitrogen pressure is 5 MPa, and the growth time is 100 h.

[0053] Comparative Example 1 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 。

[0054] Comparative Example 2 This example is generally the same as Comparative Example 1, except that similar to Example 2, the substrate is replaced with a sapphire substrate having 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 。

[0055] Comparative Example 3 This example is generally the same as Comparative Example 1, except that only the growth of the nanowire array in the first step is carried out. The obtained gallium nitride nanowires have no dislocations. The results are shown in Figure 5 and Figure 6 the transmission electron double - beam diffraction images under different conditions shown.

[0056] Comparative Example 4 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 bulk single crystal growth in the second step is directly carried out. As a result of the growth, the dislocation density is greater than 10 5 cm -2 .

[0057] Comparative Example 5 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 bulk single crystal growth in the second step is directly carried out. As a result of the growth, the microporous layer is prone to increasing the probability of inclusions, affecting the growth quality, and 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 .

[0058] 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 technical research and development process. However, these technical solutions all have the problems of uneven distribution of gallium nitride nanowires and insufficient areal density, and 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.

[0059] Based on the above examples 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.

[0060] It should be understood that the above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It cannot be used 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: include: A first flux system is used to perform a growth process based on an original substrate to obtain an intermediate crystal, wherein a plurality of gallium nitride nanowires are formed 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 metal nickel; A second flux system is used to perform secondary growth based on the intermediate crystal to form a combined growth layer that grows outward from the nanowire template layer, and finally obtain a high-quality gallium nitride crystal.

2. The flux growth method according to claim 1, characterized in that: The first flux system is a Ga-Na system; And / or, the mass fraction of metallic nickel in the first flux system is 0.5-2.5%.

3. The flux growth method according to claim 1 or 2, characterized in that: The primary growth temperature is 750-850° C., the nitrogen pressure is 2-4 MPa, and the growth time is 5-10 hours.

4. The flux growth method according to claim 1, characterized in that: The height of the gallium nitride nanowire is 1-3 μm.

5. The flux growth method according to claim 4, characterized in that: The surface density of the gallium nitride nanowires is 10 7 cm -2 above.

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

7. The flux growth method according to claim 1, characterized in that: The original substrate includes a gallium nitride seed crystal or a heterogeneous substrate with a gallium nitride layer on the surface.

8. The flux growth method according to claim 7, characterized in that: When the original substrate is a heterogeneous substrate, the thickness of the gallium nitride layer is 3-5 μm.

9. The high-quality gallium nitride crystal obtained by the flux growth method according to any one of claims 1 to 8, characterized in that: It includes an original substrate, a nanowire template layer and a merged growth layer which are sequentially stacked in a thickness direction; Wherein, the dislocation density of the merged growth layer is 10 3 cm -2 the following.

10. Application of the high-quality gallium nitride crystal according to claim 9 in the fields of solid-state lighting, lasers, and high-power electrical devices.

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