Method for improving the quality of epitaxially grown gallium nitride crystals and its application

Abstract

The present invention discloses a method for improving the quality of epitaxially grown gallium nitride crystals and its application. The method for improving the quality of epitaxially grown gallium nitride crystals comprises: performing a long-term annealing and etching treatment on an aluminum nitride buffer layer with a thickness of less than or equal to 20nm under the conditions of a temperature of 1100-1200°C, a pressure of 500-800torr, and alternating input of pure hydrogen and pure nitrogen; thereafter, depositing gallium nitride material on the aluminum nitride buffer layer. The method for improving the quality of epitaxially grown gallium nitride crystals provided by an embodiment of the present invention can stably reduce the dislocation density of the gallium nitride film by nearly 1 order of magnitude, and has good practical application value.

Description

Technical Field

[0001] The present invention particularly relates to a method for improving the quality of epitaxially grown gallium nitride crystals and an application thereof, belonging to the technical field of semiconductors. Background Art

[0002] The main challenge in heteroepitaxial GaN thin films is the crystal quality of the material. Due to the mismatch between the substrate and the epitaxial layer, a large number of dislocations are generated during the growth process. The two-step growth method, which inserts a buffer layer between the substrate and the epitaxial layer, has improved the material quality to a usable level; however, the dislocation density of the grown material is still quite high. For example, the dislocation density of the grown GaN film after low-temperature deposition on a sapphire substrate as a buffer layer is still as high as 10 8 ~10 9 cm -2 .

[0003] Currently, to shorten growth time and improve the crystal quality of gallium nitride, people have begun using aluminum nitride sputtering templates as buffer layers. Because aluminum nitride has a high nucleation density, the density of screw dislocations (the dislocations of gallium nitride material can be simply regarded as the sum of screw dislocations and edge dislocations) in the gallium nitride layer grown on it is very low; this is its advantage, but due to the high bond energy of aluminum nitride, its mobility on the surface is very poor, making it difficult to move and difficult to decompose. When traditional low-temperature gallium nitride is used as a buffer layer, a recrystallization process can be carried out under the protection of ammonia, causing small islands to slowly migrate and merge, eventually forming large three-dimensional islands, thereby reducing the formation of edge dislocations during the growth and merging process from three-dimensional to two-dimensional. However, when aluminum nitride is used as a buffer layer, the above-mentioned goal of recrystallizing aluminum nitride and transforming small islands into large three-dimensional islands is no longer feasible.

[0004] Therefore, it becomes more difficult to reduce the edge dislocations of the GaN material under the AlN buffer layer, which also becomes a key technical issue that hinders further reduction of the crystal quality of the GaN epitaxial layer. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for improving the quality of epitaxially grown gallium nitride crystals and its application, so as to overcome the deficiencies in the prior art.

[0006] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0007] An embodiment of the present invention provides a method for improving the quality of epitaxially grown gallium nitride crystals, comprising:

[0008] The aluminum nitride buffer layer is subjected to a long-term annealing and etching process at a temperature of 1100-1200°C, a pressure of 500-800 torr, and an alternating supply of pure hydrogen and pure nitrogen.

[0009] Then, a gallium nitride material is deposited on the aluminum nitride buffer layer.

[0010] An embodiment of the present invention also provides a pretreatment method for an aluminum nitride buffer layer, which includes: performing long-term annealing and etching treatment on the aluminum nitride buffer layer at a temperature of 1100-1200°C, a pressure of 500-800 torr, and alternating input of pure hydrogen and pure nitrogen.

[0011] The present invention also provides a method for preparing a gallium nitride crystal, which specifically includes:

[0012] providing a substrate with an aluminum nitride buffer layer;

[0013] Pre-treating the aluminum nitride buffer layer by using the method described above;

[0014] Depositing a thin layer of gallium nitride material on the aluminum nitride buffer layer at a temperature of 1000-1040° C., a pressure of 400-600 torr, and a low V / III ratio, wherein the low V / III ratio is N / Ga=100-900; and

[0015] The gallium nitride bulk material is continuously grown on the thin layer of gallium nitride material using conventional gallium nitride growth conditions.

[0016] Compared with the prior art, the advantages of the present invention include:

[0017] 1) The present invention provides a method for improving the quality of epitaxially grown gallium nitride crystals. This method uses an existing aluminum nitride sputtering template as a buffer layer to reduce edge dislocations while minimizing screw dislocations. This method provides an epitaxial growth method for further reducing the dislocation density of heteroepitaxial gallium nitride materials. The method is simple and easy to implement and can be implemented directly during the growth process.

[0018] 2) The method for improving the quality of epitaxially grown gallium nitride crystals provided by the embodiment of the present invention can stably reduce the dislocation density of the gallium nitride film by nearly one order of magnitude, and has great practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the rocking curve of the (002) crystal plane of the samples obtained in Examples 1, 2, and 3 of the present invention;

[0020] Figure 2 It is the rocking curve of the crystal plane of the sample (102) obtained in Example 1, Example 2 and Example 3 of the present invention. DETAILED DESCRIPTION

[0021] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0022] In order to overcome the above technical problems existing in the prior art, the present invention provides a special annealing and pretreatment epitaxial method suitable for aluminum nitride as a buffer layer, aiming to further improve the crystal quality of the subsequently grown gallium nitride thin film and reduce the dislocation density of the material; specifically, the specific process of this method mainly includes:

[0023] 1) Before growing the GaN bulk material, turn off the ammonia gas and bake the aluminum nitride for a long time at a temperature of 1100-1200°C, a pressure of 500-800 torr, and an alternating supply of pure hydrogen and pure nitrogen.

[0024] 2) Lowering the growth temperature, depositing a layer of gallium nitride on the aluminum nitride buffer layer at a temperature of 1000-1040°C, a pressure of 400-600 torr, and a low V / III ratio (N / Ga=100-900), and then performing two-dimensional growth of the gallium nitride material using conventional gallium nitride growth conditions.

[0025] The embodiment of the present invention provides a method for improving the quality of epitaxially grown gallium nitride crystals, the mechanism of which is at least:

[0026] Under the aforementioned temperature and pressure conditions, the alternating switching input of pure hydrogen and pure nitrogen can maximize the etching and purging effects of hydrogen, achieving the effect of corroding the aluminum nitride surface, so that the aluminum nitride surface is corroded to form small holes;

[0027] GaN deposited under the aforementioned growth conditions tends to grow three-dimensionally. There are two crystal orientations at the growth interface: the sidewalls of the holes and the surface of the aluminum nitride. Their interface energies are different. GaN will aggregate and grow at the low-energy interface, and the three-dimensional growth method will accelerate this aggregation effect. Slowly, the aluminum nitride buffer layer will become rough as it grows upward, completing the coarsening process that is difficult for aluminum nitride to form. Thereafter, when the two-dimensional GaN bulk material is grown under conventional GaN growth conditions, a merging process similar to that under the low-temperature GaN buffer layer will occur, thereby achieving the effect of reducing the generation of edge dislocations. It can be understood that the original planar aluminum nitride buffer layer is annealed and etched to form holes and island-like structures, so that the treated aluminum nitride buffer layer produces an interface different from that before treatment. Then, the difference in interface energy is used to carry out three-dimensional non-steady-state growth of GaN. GaN grows faster in the low-energy direction and slower in the high-energy direction, and ultimately material coarsening can be achieved.

[0028] An embodiment of the present invention provides a method for improving the quality of epitaxially grown gallium nitride crystals, comprising:

[0029] The aluminum nitride buffer layer is subjected to a long-term annealing and etching process at a temperature of 1100-1200°C, a pressure of 500-800 torr, and an alternating supply of pure hydrogen and pure nitrogen.

[0030] Then, a gallium nitride material is deposited on the aluminum nitride buffer layer.

[0031] Furthermore, the method for improving the quality of epitaxially grown gallium nitride crystals includes depositing a thin layer of gallium nitride material on an aluminum nitride buffer layer under conditions of a temperature of 1000-1040°C, a pressure of 400-600 torr, and a low V / III ratio, wherein the low V / III ratio is N / Ga=100-900.

[0032] Furthermore, the thickness of the gallium nitride material is less than or equal to 500 nm.

[0033] Furthermore, the method for improving the quality of epitaxially grown gallium nitride crystals specifically includes: after the aluminum nitride buffer layer is grown in the epitaxial reaction equipment, the input of ammonia is stopped, the temperature in the reaction chamber is increased to 1100-1200°C, the pressure is increased to 500-800 torr, and pure hydrogen and pure nitrogen are alternately input into the reaction chamber to perform long-term annealing and etching treatment on the aluminum nitride buffer layer to process the aluminum nitride buffer layer into an island structure.

[0034] Furthermore, the thickness of the aluminum nitride buffer layer is less than or equal to 20 nm.

[0035] Furthermore, in each cycle, the single introduction time of the pure hydrogen is 20-50 seconds, and the single introduction time of the pure nitrogen is 10-25 seconds.

[0036] Furthermore, the annealing and etching treatment takes longer than 5 minutes and shorter than 15 minutes.

[0037] Furthermore, the method for improving the quality of epitaxially grown gallium nitride crystals specifically includes: after completing a long-term annealing and etching treatment of the aluminum nitride buffer layer, lowering the temperature in the reaction chamber to 1000-1040°C, adjusting the pressure to 400-600 torr, and adjusting the V / III ratio to N / Ga=100-900, thereby growing a thin layer of gallium nitride material on the aluminum nitride buffer layer.

[0038] In some more specific embodiments, the method for improving the quality of epitaxially grown gallium nitride crystals further comprises: utilizing conventional gallium nitride growth conditions to continue growing a bulk gallium nitride material on the thin layer of gallium nitride material.

[0039] Furthermore, the gallium nitride bulk material includes a gallium nitride thin film.

[0040] An embodiment of the present invention also provides a pretreatment method for an aluminum nitride buffer layer, which includes: performing long-term annealing and etching treatment on the aluminum nitride buffer layer at a temperature of 1100-1200°C, a pressure of 500-800 torr, and alternating input of pure hydrogen and pure nitrogen.

[0041] Furthermore, the pretreatment method of the aluminum nitride buffer layer specifically includes: growing an aluminum nitride buffer layer on a substrate in an epitaxial reaction device, then stopping the input of ammonia, raising the temperature in the reaction chamber to 1100-1200°C, raising the pressure to 500-800 torr, and alternately inputting pure hydrogen and pure nitrogen into the reaction chamber, performing long-term annealing and etching treatment on the aluminum nitride buffer layer to process the aluminum nitride buffer layer into an island structure.

[0042] Furthermore, in each cycle, the single introduction time of the pure hydrogen is 20-50 seconds, and the single introduction time of the pure nitrogen is 10-25 seconds.

[0043] Furthermore, the annealing and etching treatment takes longer than 5 minutes and shorter than 15 minutes.

[0044] Furthermore, the substrate includes a sapphire substrate.

[0045] An embodiment of the present invention further provides a method for preparing a gallium nitride crystal, which specifically includes:

[0046] providing a substrate with an aluminum nitride buffer layer;

[0047] Pre-treating the aluminum nitride buffer layer by using the method described above;

[0048] Depositing a gallium nitride material on the aluminum nitride buffer layer at a temperature of 1000-1040° C., a pressure of 400-600 torr, and a low V / III ratio, wherein the low V / III ratio is N / Ga=100-900; and

[0049] The gallium nitride bulk material is continuously grown on the thin layer of gallium nitride material using conventional gallium nitride growth conditions.

[0050] Furthermore, the thickness of the gallium nitride material is less than or equal to 500 nm.

[0051] The following will further explain the technical solution, its implementation process and principles with reference to specific cases.

[0052] Example 1

[0053] 1) Using a sapphire substrate with an aluminum nitride sputtering template as a substrate, the substrate was first annealed at a temperature of 1020° C., a pressure of 200 torr, and an H 2 / N 2 / NH 3 mixed atmosphere for 10 minutes;

[0054] 2) A thin layer of gallium nitride material was grown on the substrate under the conditions of a temperature of 1050°C, a pressure of 200 torr, and NH3 / TMGa=1500. The growth rate of the gallium nitride material was 2.5 μm / h, and the growth time was 1 hour. The final sample obtained was marked as sample A.

[0055] Example 2

[0056] 1) Using a sapphire substrate with an aluminum nitride sputtering template as a substrate, the substrate was first annealed at a temperature of 1150° C. and a pressure of 500 torr in a cyclic alternating H2 environment and N2 environment. The duration of each cycle in the H2 environment was 45 seconds, the duration of the N2 environment was 15 seconds, and the number of cycles was 10;

[0057] 2) Gallium nitride material was grown on the substrate under the conditions of temperature of 1050° C., pressure of 200 torr, NH 3 / TMGa=1500, growth rate of 2.5 μm / h, growth time of 1 hour, and the final sample obtained was marked as sample B.

[0058] Example 3

[0059] 1) Using a sapphire substrate with an aluminum nitride sputtering template as a substrate, the substrate was first annealed at a temperature of 1150° C. and a pressure of 500 torr in a cyclic alternating H2 environment and N2 environment. The duration of each cycle in the H2 environment was 45 seconds, the duration of the N2 environment was 15 seconds, and the number of cycles was 10;

[0060] 2) Lowering the temperature to 1020°C, maintaining the pressure at 500 torr, and adjusting the NH3 / TMGa ratio to 500, thereby growing a thin layer of gallium nitride material on the aluminum nitride layer of the substrate at a growth rate of 1 μm / h for 15 minutes;

[0061] 3) Gallium nitride material was further grown on the thin layer of gallium nitride material on the substrate at a temperature of 1050° C., a pressure of 200 torr, and NH 3 / TMGa = 1500, with a growth rate of 2.5 μm / h and a growth time of 1 hour. The final sample obtained was marked as sample C.

[0062] It should be noted that the sapphire substrates with aluminum nitride sputtering templates in Examples 1 to 3 are all made of the same material and have the same parameters, and the growth equipment used in Examples 1, 2, and 3 is also the same equipment.

[0063] The three samples obtained in Examples 1-3 were subjected to X-ray diffraction tests respectively, and the rocking curves of the (002) and (102) crystal planes of the three samples were obtained as follows: Figure 1 and Figure 2 As shown in the figure, the half-peak width of the former represents the amount of screw dislocations to a certain extent, while the latter represents edge dislocations.

[0064] Specifically, by Figure 1 and Figure 2 It can be seen that the (002) half-height widths of sample A, sample B, and sample C are 81 arc seconds, 99 arc seconds, and 118 arc seconds respectively; the (102) half-height widths of sample A, sample B, and sample C are 504 arc seconds, 216 arc seconds, and 169 arc seconds respectively. Figure 1 It can be seen that the (102) half-width can be significantly reduced through special annealing treatment, and the (102) half-width can be further reduced by pre-treatment growth. At the same time, we also see that the (002) half-width of the sample is slowly increasing, but it still maintains the advantage of low screw dislocation of the aluminum nitride buffer layer.

[0065] From the above half-height width, it can be estimated that the dislocation density of sample A, sample B, and sample C corresponds to 5.5x10 8 cm -2 , 1.1x10 8 cm -2 and 7.3x10 7 cm -2 The two-step special treatment epitaxial growth method of the present invention can stably reduce the dislocation density of the gallium nitride film by nearly one order of magnitude, which has great practical application value.

[0066] A method for improving the quality of epitaxially grown gallium nitride crystals provided by an embodiment of the present invention is based on the existing aluminum nitride sputtering template as a buffer layer, with the purpose of reducing edge dislocations under low screw dislocations, and providing an epitaxial method for further reducing the dislocation density of heteroepitaxial gallium nitride materials. The method is simple and easy to implement and can be implemented directly during the growth process. Using the method for improving the quality of epitaxially grown gallium nitride crystals provided by an embodiment of the present invention, the dislocation density of gallium nitride films can be stably reduced by nearly one order of magnitude, and has great practical application value.

[0067] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A method for improving the quality of epitaxially grown gallium nitride crystals, characterized in that include: An aluminum nitride buffer layer is grown in an epitaxial reaction device, and then the input of ammonia is stopped, and the temperature in the reaction chamber is increased to 1100-1200° C., the pressure is increased to 500-800 torr, and pure hydrogen and pure nitrogen are alternately input into the reaction chamber to perform a long-term annealing and etching treatment on the aluminum nitride buffer layer to form an island structure. In each cycle, the single introduction time of the pure hydrogen is 20-50 seconds, and the single introduction time of the pure nitrogen is 10-25 seconds; Afterwards, three-dimensional non-steady-state growth of gallium nitride is performed on the aluminum nitride buffer layer under the conditions of a temperature of 1000-1040°C, a pressure of 400-600 torr and a low V / III ratio to form a thin layer of gallium nitride material, wherein the low V / III ratio is N / Ga=100-900.

2. The method for improving the quality of epitaxially grown gallium nitride crystals according to claim 1, characterized in that: The thickness of the gallium nitride material is less than or equal to 500 nm.

3. The method for improving the quality of epitaxially grown gallium nitride crystals according to claim 1, characterized in that: The thickness of the aluminum nitride buffer layer is less than or equal to 20 nm.

4. The method for improving the quality of epitaxially grown gallium nitride crystals according to claim 1, characterized in that: The time of the annealing and etching treatment is greater than 5 minutes and less than 15 minutes.

5. The method for improving the quality of epitaxially grown gallium nitride crystals according to claim 1, characterized in that The method also includes: using conventional growth conditions of gallium nitride to continue growing a gallium nitride bulk material on the thin layer of gallium nitride material.

6. The method for improving the quality of epitaxially grown gallium nitride crystals according to claim 5, characterized in that: The gallium nitride bulk material includes a gallium nitride thin film.

7. A method for preparing gallium nitride crystal, characterized in that Specifically include: An aluminum nitride buffer layer is grown on a substrate in an epitaxial reaction device, and then the input of ammonia is stopped, and the temperature in the reaction chamber is increased to 1100-1200° C., the pressure is increased to 500-800 torr, and pure hydrogen and pure nitrogen are alternately input into the reaction chamber to perform long-term annealing and etching treatment on the aluminum nitride buffer layer to form an island structure. In each cycle, the single introduction time of the pure hydrogen is 20-50 seconds, and the single introduction time of the pure nitrogen is 10-25 seconds; Depositing a thin layer of gallium nitride material on the aluminum nitride buffer layer at a temperature of 1000-1040° C., a pressure of 400-600 torr and a low V / III ratio of N / Ga=100-900; and The gallium nitride bulk material is continuously grown on the thin layer of gallium nitride material using conventional growth conditions of gallium nitride.

8. The method for preparing gallium nitride crystal according to claim 7, characterized in that: The thickness of the gallium nitride material is less than or equal to 500 nm.

9. The method for preparing gallium nitride crystal according to claim 7, characterized in that: The time of the annealing and etching treatment is greater than 5 minutes and less than 15 minutes.

10. The method for preparing gallium nitride crystal according to claim 7, characterized in that: The substrate includes a sapphire substrate.

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