Method for improving quality of nitrogen polar gallium nitride heterojunction thin film material of diamond substrate

Abstract

The invention discloses a method for improving the quality of a diamond substrate nitrogen polar gallium nitride heterojunction thin film material, and the method comprises the following steps: firstly preparing beveled angle gallium polar GaN on a beveled angle substrate, combining the beveled angle gallium polar GaN with diamond in a bonding manner, and then sequentially removing the substrate and a composite buffer layer by adopting a laser lift-off (or polishing) and dry etching method, so as to improve the quality of the diamond substrate nitrogen polar gallium nitride heterojunction thin film material. Forming a diamond / beveled nitrogen polar GaN substrate for nitrogen polar GaN epitaxial growth, and finally growing the nitrogen polar GaN heterojunction thin film material by adopting chemical vapor deposition equipment or molecular beam epitaxy equipment. By adopting the method disclosed by the invention, the quality of the nitrogen polar material can be greatly improved, and the surface quality, the crystallization quality and the electrical property of the diamond substrate nitrogen polar gallium nitride thin film heterojunction material are improved by utilizing the characteristic that the nitrogen polar beveled gallium nitride is easier to grow; the method is favorable for improving the performance of a diamond substrate nitrogen polar gallium nitride heterojunction thin film material and a device, and is suitable for a high-frequency power device.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor epitaxial materials, and in particular relates to a method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates. Background Art

[0002] Gallium nitride (GaN) materials have properties such as high electron mobility and high breakdown, and can meet the application requirements of RF devices such as higher power density, higher operating frequency, smaller size and more harsh environment. They are an important foundation and key support for the manufacture of GaN microwave power devices and circuits. Nitrogen-polarity GaN-based devices prepared with nitrogen-polarity GaN materials have lower ohmic contact resistance, better carrier limiting threshold, stronger short channel effect suppression ability and other characteristics, which makes nitrogen-polarity GaN materials more advantageous in high-frequency and high-power microwave device applications. With the continuous improvement of epitaxial material crystal quality and the continuous improvement of device technology, microwave and millimeter wave devices and circuits developed based on nitrogen-polarity GaN have higher and higher operating frequencies and higher and higher output powers. At this time, the problem of "heat" has become more and more prominent, and has gradually become one of the important issues restricting the device from upgrading to higher performance. Using high thermal conductivity diamond as the substrate for high-frequency, high-power GaN devices can reduce the impact of the self-heating effect of GaN high-power devices on indicators such as power and efficiency. Therefore, introducing diamond into high-frequency, high-power GaN-based microwave power devices and circuits to solve the heat dissipation problem of the devices has become an international research hotspot in recent years.

[0003] Diamond-based substrate transfer technology, single-crystal diamond-based direct epitaxy, and device surface coating technology based on nanodiamond films all hold significant potential for addressing heat dissipation in high-frequency, high-power GaN devices. However, the integration of GaN-on-diamond wafers is susceptible to stress, warping, cracks, interface roughness, and high thermal boundary resistance. The interface between the transition layer and the buffer layer hinders heat flow from the device channel, significantly impacting device performance. GaN-on-diamond grown using direct epitaxy has the lowest theoretical thermal resistance, but due to large lattice and thermal mismatches, the crystal quality and mobility of GaN epitaxial materials still lag significantly behind those grown on traditional sapphire, silicon, silicon carbide, and free-standing GaN substrates. Diamond-GaN composite substrates fabricated by bonding GaN thin films to diamond can effectively address these lattice and thermal mismatches. However, the resulting nitrogen-polar GaN materials exhibit numerous defects, such as threading dislocations, vacancies, and inversion domains, which severely degrade the film's crystal quality. Inversion domain defects extend upward to the surface, forming numerous hexagonal defects. The high surface roughness and defect density cause scattering of the two-dimensional electron gas in the GaN channel, resulting in reduced mobility and severely limiting the performance of nitrogen-polar GaN materials.

[0004] In recent years, patents related to diamond-based gallium nitride heterojunction materials have primarily focused on gallium-polarized gallium nitride, while patents related to the preparation of nitrogen-polarized gallium nitride materials on diamond substrates remain relatively rare. For example, CN108538723A discloses a diamond-based nitrogen-polarized gallium nitride device and its manufacturing method. This method only provides a method for controlling the polarity of nitrogen-polarized gallium nitride on a diamond substrate, but does not address how to improve the quality of nitrogen-polarized GaN films produced through secondary high-temperature epitaxy. CN116936361A discloses a diamond-substrate nitrogen-polarity gallium nitride heterojunction material and a preparation method thereof. The material adopts a bonding-first-bevel-then-angle-cutting scheme, and mechanical polishing is used to make the surface of the diamond-GaN composite substrate template present a bevel angle. After the bevel angle is achieved, the GaN thickness in the template exhibits significant deviations. For example, the thickness difference between the thickest and thinnest parts of a 1mm-sized GaN with a 2° bevel angle reaches more than 1μm, which affects the quality of the subsequent nitrogen-polarity GaN heterojunction film. Furthermore, this method is difficult to prepare and control, making it difficult to meet the requirements for industrial applications of nitrogen-polarity GaN materials. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for improving the quality of nitrogen-polarity gallium nitride heterojunction thin film materials on diamond substrates. By growing nitrogen-polarity GaN materials on silicon carbide or sapphire substrates with a certain bevel angle, the migration of atoms on the growth surface can be promoted, surface hexagonal island defects are eliminated, and the quality of the nitrogen-polarity material is greatly improved. By utilizing the characteristic that nitrogen-polarity bevel-cut gallium nitride is easier to grow, the surface quality, crystallization quality and electrical properties of nitrogen-polarity gallium nitride thin film heterojunction materials on diamond substrates are improved. This method is beneficial to improving the performance of nitrogen-polarity gallium nitride heterojunction thin film materials and devices on diamond substrates, and is suitable for high-frequency power devices.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for improving the quality of diamond substrate nitrogen-polar gallium nitride heterojunction thin film material, comprising the following steps:

[0008] Step 1) Selecting a silicon carbide or sapphire pattern substrate with a specific bevel angle and placing it on a susceptor in a reaction chamber of a high-temperature chemical vapor deposition device;

[0009] Step 2) adjusting the pressure of the reaction chamber, introducing hydrogen into the reaction chamber, raising the temperature, and baking the substrate in a hydrogen atmosphere to remove surface oxides and contamination;

[0010] Step 3) Maintaining the flow of hydrogen, adjusting the pressure and temperature of the reaction chamber, and introducing ammonia, sequentially growing a composite buffer layer and a gallium nitride epitaxial layer on the silicon carbide or sapphire pattern substrate having a specific bevel angle, thereby forming a bevel angled silicon carbide or sapphire pattern substrate gallium nitride material;

[0011] Step 4) After the growth is completed, the growth source is turned off, the temperature is lowered in an ammonia atmosphere, and finally the beveled silicon carbide or sapphire pattern substrate GaN material is removed;

[0012] Step 5) using a thin film bonding device to bond a diamond substrate to the surface of the beveled silicon carbide or sapphire pattern substrate gallium nitride material;

[0013] Step 6) Inverting the beveled silicon carbide or sapphire patterned substrate GaN material processed in step 5), removing the beveled silicon carbide or sapphire substrate by laser lift-off or polishing, and dry-etching the composite buffer layer to form a diamond / beveled nitrogen-polar GaN substrate;

[0014] Step 7) placing the diamond / bevel-cut nitrogen-polarity gallium nitride substrate in a metal organic chemical vapor deposition device or a molecular beam epitaxy device, introducing a reaction source, and sequentially growing a nitrogen-polarity aluminum nitride buffer layer, a nitrogen-polarity gallium nitride buffer layer, a nitrogen-polarity aluminum nitride barrier layer, an aluminum nitride isolation layer, and a gallium nitride channel layer on the diamond / bevel-cut nitrogen-polarity gallium nitride substrate to form a diamond substrate nitrogen-polarity gallium nitride thin film heterojunction material;

[0015] Step 8) After the epitaxial growth is completed, the growth source is turned off, and the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material is removed after cooling.

[0016] Preferably, the specific bevel angle in step 1) is ≤8°.

[0017] Preferably, in step 2), the pressure of the reaction chamber is adjusted to 50-500 mbar, the temperature of the heating is 1000-1100° C., and the time of baking the substrate is 5-15 minutes.

[0018] Preferably, in step 3), the pressure of the reaction chamber is adjusted to 50-200 mbar and the temperature is adjusted to 700-1150°C.

[0019] Preferably, in step 3), the composite buffer layer consists of an aluminum nitride nucleation layer, a gallium nitride buffer layer and an aluminum nitride barrier layer, wherein the thickness of the aluminum nitride nucleation layer is 10 to 500 nm, the thickness of the gallium nitride buffer layer is 50 to 500 nm, and the thickness of the aluminum nitride barrier layer is 10 to 50 nm; and the thickness of the gallium nitride epitaxial layer is 300 to 3000 nm.

[0020] Preferably, in step 7), the thickness of the nitrogen-polar aluminum nitride buffer layer is 10 to 200 nm; the thickness of the nitrogen-polar gallium nitride buffer layer is 50 to 4000 nm; the thickness of the nitrogen-polar aluminum nitride barrier layer is 3 to 30 nm; the thickness of the aluminum nitride isolation layer is 0 to 1 nm; and the thickness of the gallium nitride channel layer is 5 to 50 nm.

[0021] Preferably, the nitrogen-polar aluminum nitride barrier layer further includes metal indium, metal scandium or metal gallium.

[0022] The diamond substrate nitrogen-polarity gallium nitride thin film heterojunction material prepared by the above method comprises, from bottom to top, a diamond base, a beveled nitrogen-polarity gallium nitride epitaxial layer, a nitrogen-polarity aluminum nitride buffer layer, a nitrogen-polarity gallium nitride buffer layer, a nitrogen-polarity aluminum nitride barrier layer, an aluminum nitride isolation layer and a gallium nitride channel layer.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention adopts the method of inverted epitaxy after bonding gallium-polar gallium nitride to diamond on a bevel-cut substrate to grow high-quality nitrogen-polar materials, thereby achieving the control of the growth polarity of gallium nitride on a diamond substrate and improving the surface quality. Gallium-polar gallium nitride with the same bevel angle is grown on a substrate with a bevel angle not exceeding 8°, and is combined with diamond by bonding or deposition. The gallium-polar gallium nitride substrate carrier and the composite buffer layer are then removed to form a diamond substrate nitrogen-polar gallium nitride template with a certain deflection angle. The bevel angle characteristics of gallium nitride are used to guide the growth of higher-quality nitrogen-polar heterojunctions, thereby further improving the surface quality and electrical properties of the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material.

[0025] (2) The bevel-cut substrate (such as silicon carbide, sapphire, etc.) used for the growth of gallium-polarity gallium nitride in the present invention has its surface patterned. The patterned surface is used to promote the lateral epitaxial growth of bevel-cut gallium nitride, solve the step bunching problem in the growth of gallium-polarity bevel-cut gallium nitride, thereby effectively improving the surface quality of the gallium nitride material on the bevel-cut substrate and meeting the requirements for direct bonding of diamond on the surface after epitaxy.

[0026] (3) The beveled silicon carbide, sapphire substrate and patterned preparation technology used in the present invention have all been industrialized and applied. The diamond-beveled nitrogen-polar gallium nitride template preparation method prepared by the present invention has higher process stability and stronger promotion ability, and has certain industrial application value.

[0027] (4) Compared with CN116936361A, the present invention adopts a scheme of beveling first and then bonding, which achieves uniform GaN thickness in the template after beveling, and the angle is the same as that of the beveled substrate used for guidance, with higher control accuracy, and is more suitable for the industrial application and promotion of wafer-level nitrogen-polarity GaN heterojunction thin film products. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the beveled silicon carbide (or sapphire) pattern substrate gallium nitride material combined with the diamond substrate;

[0029] Figure 2Schematic diagram of the structure of nitrogen-polar gallium nitride heterojunction thin film material on diamond substrate;

[0030] Figure 1 、 2 Middle: 1-1, silicon carbide (or sapphire) patterned substrate with a specific bevel angle; 1-2, aluminum nitride nucleation layer; 1-3, gallium nitride buffer layer; 1-4, aluminum nitride barrier layer; 1-5, gallium nitride epitaxial layer; 1-6, diamond substrate; 1-7, composite buffer layer; 2-1, diamond / bevel-angle nitrogen-polar gallium nitride substrate; 2-2, nitrogen-polar aluminum nitride buffer layer; 2-3, nitrogen-polar gallium nitride buffer layer; 2-4, nitrogen-polar aluminum (gallium) nitride (indium / scandium) nitride barrier layer; 2-5, aluminum nitride isolation layer; 2-6, gallium nitride channel layer;

[0031] Figure 3 Optical microscope images of the surface morphology of diamond substrate bevel-cut nitrogen-polarity gallium nitride heterojunction thin film materials: A is a diamond / 4° nitrogen-polarity gallium nitride heterojunction thin film material; B is a diamond / 2° nitrogen-polarity gallium nitride heterojunction thin film material; C is a diamond / 0° nitrogen-polarity gallium nitride heterojunction thin film material;

[0032] Figure 4 The contact Hall test results of diamond substrate bevel-cut nitrogen-polarity gallium nitride heterojunction thin film material are shown in Figure 1: A is diamond / 0° nitrogen-polarity gallium nitride heterojunction thin film material; B is diamond / 4° nitrogen-polarity gallium nitride heterojunction thin film material. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] A method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates, comprising the following steps:

[0035] (1) A silicon carbide (or sapphire) patterned substrate with a specific bevel angle (no more than 8°) is selected and placed on a susceptor in the reaction chamber of a high-temperature chemical vapor deposition (HTCVD) device. Beveled substrate processing can be performed using beveled silicon carbide or sapphire, and nano-patterning technology is used to improve the surface quality of the GaN material on the beveled substrate, making it more conducive to subsequent diamond surface bonding.

[0036] (2) Set the pressure of the reaction chamber to 50-500 mbar, introduce hydrogen, heat the reaction chamber to 1000-1100°C, and bake the substrate in a hydrogen atmosphere for 5-15 minutes to remove surface oxides and contamination.

[0037] (3) Maintain hydrogen flow, set the pressure of the reaction chamber to 50-200 mbar, the temperature of the reaction chamber to 700-1150°C, and introduce ammonia and other reaction sources, such as Figure 1As shown, a composite buffer layer 1-7 consisting of an aluminum nitride nucleation layer 1-2 (thickness 10-500nm), a gallium nitride buffer layer 1-3 (thickness 50-500nm), and an aluminum nitride barrier layer 1-4 (thickness 10-50nm) is sequentially grown on a silicon carbide (or sapphire) patterned substrate 1-1 with a specific off-cut angle, followed by a gallium nitride epitaxial layer 1-5 (thickness 300-3000nm), forming a gallium nitride material on a silicon carbide (or sapphire) patterned substrate with an off-cut angle. In the composite buffer layer 1-7 consisting of the aluminum nitride nucleation layer 1-2, gallium nitride buffer layer 1-3, and aluminum nitride barrier layer 1-4, the aluminum nitride nucleation layer 1-2 can block impurity diffusion from the substrate, the gallium nitride buffer layer 1-3 can promote consistent growth polarity, and the aluminum nitride barrier layer 1-4 can achieve quantitative etching of gallium nitride, thereby achieving higher-quality bonding of the gallium nitride epitaxial layer 1-5 to the diamond substrate 1-6.

[0038] (4) After the growth is completed, the growth source is turned off, the temperature is lowered in an ammonia atmosphere, and finally the beveled silicon carbide (or sapphire) pattern substrate gallium nitride material is taken out.

[0039] (5) Figure 1 As shown, a thin film bonding device is used to bond a diamond substrate 1-6 to the surface of the gallium nitride material of a beveled silicon carbide (or sapphire) pattern substrate.

[0040] (6) Figure 2 As shown, the material bonded to the diamond substrate 1-6 is inverted, the beveled silicon carbide (or sapphire) substrate is removed by laser lift-off or polishing, and the composite buffer layer 1-7 is removed by dry etching to form a diamond / beveled nitrogen-polarity gallium nitride substrate 2-1. Diamond is bonded to the gallium-polarity gallium nitride surface of the beveled substrate, and the beveled substrate and aluminum nitride nucleation layer are removed to form a diamond / beveled nitrogen-polarity gallium nitride substrate 2-1 suitable for nitrogen-polarity gallium nitride epitaxial growth. The beveled angle characteristics of gallium nitride are utilized to guide the growth of higher-quality nitrogen-polarity gallium nitride heterojunctions, thereby improving the quality of nitrogen-polarity GaN thin film heterojunction materials on diamond substrates.

[0041] (7) Figure 2 As shown, a diamond / bevel-cut nitrogen-polar gallium nitride substrate 2-1 is placed in a metal organic chemical vapor deposition device or a molecular beam epitaxy device, and a reaction source is introduced to sequentially grow a nitrogen-polar aluminum nitride buffer layer 2-2 (thickness 10 to 200 nm), a nitrogen-polar gallium nitride buffer layer 2-3 (thickness 50 to 4000 nm), a nitrogen-polar nitride (indium / scandium) aluminum (gallium) barrier layer 2-4 (thickness 3 to 30 nm), an aluminum nitride isolation layer 2-5 (thickness 0 to 1 nm) and a gallium nitride channel layer 2-6 (thickness 5 to 50 nm) thereon to form a diamond substrate nitrogen-polar gallium nitride thin film heterojunction material.

[0042] (8) After the epitaxial growth is completed, the growth source is turned off, and after cooling, the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material is taken out.

[0043] The diamond substrate nitrogen-polar gallium nitride heterojunction thin film material prepared based on the above method is as follows: Figure 2 As shown, from bottom to top, it includes a diamond / bevel-cut nitrogen-polarity gallium nitride substrate 2-1 (composed of a diamond base 1-6 and a bevel-cut nitrogen-polarity gallium nitride epitaxial layer 1-5), a nitrogen-polarity aluminum nitride buffer layer 2-2, a nitrogen-polarity gallium nitride buffer layer 2-3, a nitrogen-polarity nitride (indium / scandium) aluminum (gallium) barrier layer 2-4, an aluminum nitride isolation layer 2-5 and a gallium nitride channel layer 2-6.

[0044] Example 1

[0045] A method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates, comprising the following steps:

[0046] (1) A 4-inch 2° silicon carbide patterned substrate was selected and placed on a susceptor in a reaction chamber of a high-temperature chemical vapor deposition device.

[0047] (2) The pressure of the reaction chamber was set to 150 mbar, hydrogen was introduced, the temperature of the reaction chamber was raised to 1080°C, and the substrate was baked in a hydrogen atmosphere for 5 minutes to remove surface oxides and contamination.

[0048] (3) Maintaining the flow of hydrogen, setting the pressure of the reaction chamber to 100 mbar, the temperature of the reaction chamber to 1100°C, introducing ammonia and other reaction sources, and sequentially growing a composite buffer layer consisting of a 30 nm thick aluminum nitride nucleation layer, an 80 nm thick gallium nitride buffer layer, and a 20 nm thick aluminum nitride barrier layer, and a 1000 nm thick gallium nitride epitaxial layer on a 2° silicon carbide patterned substrate to form a 2° silicon carbide patterned substrate bevel-cut gallium nitride material.

[0049] (4) After the growth is completed, the growth source is turned off, the temperature is lowered in an ammonia atmosphere, and finally the 2° bevel angle GaN material on the SiC pattern substrate is removed.

[0050] (5) A 3-inch polycrystalline diamond substrate was bonded to the surface of the 2° bevel angle GaN material on the silicon carbide patterned substrate using a thin film bonding device.

[0051] (6) The 2° silicon carbide pattern substrate beveled gallium nitride material is inverted, the beveled silicon carbide substrate is removed by polishing, and the composite buffer layer is removed by dry etching to form a diamond / 2° nitrogen polar gallium nitride substrate.

[0052] (7) Placing the diamond / 2° nitrogen-polar gallium nitride substrate in a metal organic chemical vapor deposition device or a molecular beam epitaxy device, introducing a reaction source, and sequentially growing a 50 nm thick nitrogen-polar aluminum nitride buffer layer, a 1500 nm thick nitrogen-polar gallium nitride buffer layer, a 20 nm thick nitrogen-polar aluminum gallium nitride barrier layer, a 1 nm thick aluminum nitride isolation layer, and a 20 nm thick gallium nitride channel layer thereon to form a diamond substrate nitrogen-polar gallium nitride heterojunction thin film material.

[0053] (8) After the epitaxial growth is completed, the growth source is turned off, and after cooling, the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material is taken out.

[0054] Example 2

[0055] A method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates, comprising the following steps:

[0056] (1) A 4-inch 4° silicon carbide patterned substrate was selected and placed on a susceptor in a reaction chamber of a high-temperature chemical vapor deposition device.

[0057] (2) The pressure of the reaction chamber was set to 150 mbar, hydrogen was introduced, the temperature of the reaction chamber was raised to 1080°C, and the substrate was baked in a hydrogen atmosphere for 5 minutes to remove surface oxides and contamination.

[0058] (3) Maintaining the flow of hydrogen, setting the pressure of the reaction chamber to 100 mbar, the temperature of the reaction chamber to 1100°C, introducing ammonia and other reaction sources, and sequentially growing a composite buffer layer consisting of a 30 nm thick aluminum nitride nucleation layer, an 80 nm thick gallium nitride buffer layer, and a 20 nm thick aluminum nitride barrier layer, and a 1000 nm thick gallium nitride epitaxial layer on a 4° silicon carbide patterned substrate to form a 4° silicon carbide patterned substrate bevel angle gallium nitride material.

[0059] (4) After the growth is completed, the growth source is turned off, the temperature is lowered in an ammonia atmosphere, and finally the 4° bevel angle GaN material on the SiC pattern substrate is taken out.

[0060] (5) A 3-inch polycrystalline diamond substrate was bonded to the surface of the GaN material with a 4° bevel angle on a silicon carbide patterned substrate using a thin film bonding device.

[0061] (6) The 4° beveled GaN material on the SiC pattern substrate is inverted, the beveled SiC substrate is removed by laser lift-off, and the composite buffer layer is removed by dry etching to form a diamond / 4° nitrogen-polar GaN substrate.

[0062] (7) Placing the diamond / 4° nitrogen-polar gallium nitride substrate in a metal organic chemical vapor deposition device or a molecular beam epitaxy device, introducing a reaction source, and sequentially growing a 50 nm thick nitrogen-polar aluminum nitride buffer layer, a 1500 nm thick nitrogen-polar gallium nitride buffer layer, a 20 nm thick nitrogen-polar aluminum gallium nitride barrier layer, a 1 nm thick aluminum nitride isolation layer, and a 20 nm thick gallium nitride channel layer thereon to form a diamond substrate nitrogen-polar gallium nitride heterojunction thin film material.

[0063] (8) After the epitaxial growth is completed, the growth source is turned off, and after cooling, the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material is taken out.

[0064] Test Example 1

[0065] In the above-mentioned Examples 1 and 2, gallium-polarity gallium nitride materials grown on 2° and 4° silicon carbide patterned substrates are bonded to a diamond substrate, respectively. The silicon carbide substrate and the composite buffer layer are removed by polishing or laser lift-off and dry etching, thereby realizing the preparation of a diamond / 2° nitrogen-polarity gallium nitride template and a diamond / 4° nitrogen-polarity gallium nitride template, respectively. Based on the above templates, the preparation of diamond substrate nitrogen-polarity gallium nitride heterojunction thin film materials is realized.

[0066] The diamond / 2° nitrogen-polarity gallium nitride heterojunction thin film materials and the diamond / 4° nitrogen-polarity gallium nitride heterojunction thin film materials prepared in Examples 1 and 2 were observed using an optical microscope and compared with the diamond / 0° nitrogen-polarity gallium nitride heterojunction thin film material prepared using a conventional positive crystal orientation silicon carbide substrate.

[0067] Observation results such as Figure 3 As shown, the diamond / 0° nitrogen polarity gallium nitride heterojunction thin film material prepared by conventional methods is as follows Figure 3 As shown in C, the surface hexagonal defects are densely distributed and the surface undulations are large; and the diamond substrate nitrogen-polar gallium nitride heterojunction thin film materials prepared by the scheme of the present invention are respectively as shown in Figure 3 Medium A (diamond / 4° nitrogen-polar gallium nitride heterojunction thin film material) and Figure 3 As shown in B (diamond / 2° nitrogen-polar gallium nitride heterojunction thin film material), it can be seen that the material surface is relatively smooth and the hexagonal defects are greatly reduced.

[0068] In order to analyze the effect of this method on improving the electrical properties of nitrogen-polarized gallium nitride heterojunction materials, we conducted a comparative analysis of the Van der Pauw test of heterojunction materials. Figure 4 As shown in the figure, compared with the diamond / 0° nitrogen-polarity gallium nitride heterojunction thin film material grown by conventional methods, the mobility of the diamond / 2° nitrogen-polarity gallium nitride heterojunction thin film material prepared by the scheme of the present invention is increased from 519 cm 2 / (V·s)( Figure 4 Middle A) Raised to 844cm2 / (V·s)( Figure 4 Middle B).

[0069] It can be seen that the diamond substrate nitrogen-polar gallium nitride thin film heterojunction material grown by the method provided by the present invention exhibits more excellent surface quality and electrical properties, the surface hexagonal defects are significantly reduced, and the heterojunction two-dimensional electron gas mobility is greatly improved, meeting the performance improvement requirements for device use.

[0070] The embodiments described above are only some of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but merely represents selected embodiments of the present invention. The scope of protection of the present invention shall be based on the scope required by the claims. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates, characterized in that: The following steps are involved: Step 1) Selecting a silicon carbide or sapphire pattern substrate with a specific bevel angle and placing it on a susceptor in a reaction chamber of a high-temperature chemical vapor deposition device; Step 2) adjusting the pressure of the reaction chamber, introducing hydrogen into the reaction chamber, raising the temperature, and baking the substrate in a hydrogen atmosphere to remove surface oxides and contamination; Step 3) Maintaining the flow of hydrogen, adjusting the pressure and temperature of the reaction chamber, and introducing ammonia, sequentially growing a composite buffer layer and a gallium nitride epitaxial layer on the silicon carbide or sapphire pattern substrate having a specific bevel angle, thereby forming a bevel angled silicon carbide or sapphire pattern substrate gallium nitride material; Step 4) After the growth is completed, the growth source is turned off, the temperature is lowered in an ammonia atmosphere, and finally the beveled silicon carbide or sapphire pattern substrate GaN material is removed; Step 5) using a thin film bonding device to bond a diamond substrate to the surface of the beveled silicon carbide or sapphire pattern substrate gallium nitride material; Step 6) Inverting the beveled silicon carbide or sapphire patterned substrate GaN material processed in step 5), removing the beveled silicon carbide or sapphire substrate by laser lift-off or polishing, and dry-etching the composite buffer layer to form a diamond / beveled nitrogen-polar GaN substrate; Step 7) placing the diamond / bevel-cut nitrogen-polarity gallium nitride substrate in a metal organic chemical vapor deposition device or a molecular beam epitaxy device, introducing a reaction source, and sequentially growing a nitrogen-polarity aluminum nitride buffer layer, a nitrogen-polarity gallium nitride buffer layer, a nitrogen-polarity aluminum nitride barrier layer, an aluminum nitride isolation layer, and a gallium nitride channel layer on the diamond / bevel-cut nitrogen-polarity gallium nitride substrate to form a diamond substrate nitrogen-polarity gallium nitride thin film heterojunction material; Step 8) After the epitaxial growth is completed, the growth source is turned off, and the diamond substrate nitrogen-polar gallium nitride heterojunction thin film material is removed after cooling.

2. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 1, characterized in that: The specific bevel angle in step 1) is ≤8°.

3. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 1, characterized in that: In step 2), the pressure of the reaction chamber is adjusted to 50-500 mbar, the temperature of the heating is 1000-1100° C., and the time of baking the substrate is 5-15 minutes.

4. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 1, characterized in that: Step 3) The pressure of the reaction chamber is adjusted to 50-200 mbar and the temperature is adjusted to 700-1150°C.

5. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 1, characterized in that: Step 3) The composite buffer layer consists of an aluminum nitride nucleation layer, a gallium nitride buffer layer and an aluminum nitride barrier layer, wherein the thickness of the aluminum nitride nucleation layer is 10 to 500 nm, the thickness of the gallium nitride buffer layer is 50 to 500 nm, and the thickness of the aluminum nitride barrier layer is 10 to 50 nm; the thickness of the gallium nitride epitaxial layer is 300 to 3000 nm.

6. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 1, characterized in that: Step 7) The thickness of the nitrogen-polar aluminum nitride buffer layer is 10 to 200 nm; the thickness of the nitrogen-polar gallium nitride buffer layer is 50 to 4000 nm; the thickness of the nitrogen-polar aluminum nitride barrier layer is 3 to 30 nm; the thickness of the aluminum nitride isolation layer is 0 to 1 nm; and the thickness of the gallium nitride channel layer is 5 to 50 nm.

7. The method for improving the quality of nitrogen-polar gallium nitride heterojunction thin film materials on diamond substrates according to claim 6, characterized in that: The nitrogen-polar aluminum nitride barrier layer further includes metal indium, metal scandium or metal gallium.

8. The diamond substrate nitrogen-polar gallium nitride thin film heterojunction material prepared by the method according to any one of claims 1 to 7, characterized in that: The diamond substrate nitrogen-polarity gallium nitride thin film heterojunction material comprises, from bottom to top, a diamond base, a beveled nitrogen-polarity gallium nitride epitaxial layer, a nitrogen-polarity aluminum nitride buffer layer, a nitrogen-polarity gallium nitride buffer layer, a nitrogen-polarity aluminum nitride barrier layer, an aluminum nitride isolation layer and a gallium nitride channel layer.

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