GaN thin film grown on Si substrate and preparation method thereof

Abstract

Embodiments of the present application provide a GaN film grown on a Si substrate and a preparation method thereof. The GaN film grown on the Si substrate includes at least a Si substrate and a transition layer, a GaN buffer layer, a GaN channel layer, and a barrier layer epitaxially grown in sequence on the Si substrate. The GaN buffer layer includes a first GaN layer and a second GaN layer. The first GaN layer, the second GaN layer, and the GaN channel layer are epitaxially grown under first conditions, second conditions, and third conditions, respectively, and deposited step by step. The first GaN layer is first grown at an extremely low V / III ratio as a stress retention layer, so that the first GaN layer can introduce sufficient compressive stress to balance subsequent thermal stress and improve the film layer's resistance to bending deformation. The second GaN layer with high impedance is grown at a lower V / III ratio, which can effectively increase the C doping concentration, thereby improving the voltage resistance of the GaN film, and further improving the overall voltage resistance effect of the power device.

Description

Technical Field

[0001] The present invention relates to the technical field of GaN thin films, and in particular to a GaN thin film grown on a Si substrate and a preparation method thereof. Background Art

[0002] Currently, Si (silicon) substrates are widely used in the production and fabrication of GaN (gallium nitride)-based semiconductor devices due to their mature fabrication process, good thermal conductivity, high crystal quality, and low production cost. However, due to the significant lattice mismatch (16.9%) and thermal mismatch (54%) between Si and GaN, as well as melt-back etching issues, a large number of threading dislocations are easily generated during the growth process, leading to cracks in the GaN epitaxial films and even epitaxial failure.

[0003] In view of this, it is usually necessary to first grow a buffer layer on the Si substrate, and then use the buffer layer as the bottom layer to grow epitaxial layers such as GaN thin film, GaN channel layer, isolation layer, etc. However, in order to overcome problems such as thermal stress adaptation, when growing GaN thin film on the buffer layer, it is usually necessary to grow a stress release layer at a lower speed (about 2μm / h) or low temperature. What's more, it is necessary to grow GaN thin film at an ultra-low speed of less than 1μm / h. Although the controllability is relatively high, its efficiency is extremely low, and it also fails to fully utilize the characteristics of the film layer to resist the thermal stress accumulated in the bottom layer. For power devices prepared by such thin films, although the above method can obtain better film quality, for the device, the quality of such film layers has limited impact on the performance of the device, but it brings about cumbersome process flow.

[0004] Therefore, it is necessary to develop a GaN thin film grown on a Si substrate and a preparation method thereof to solve the above technical problems. Summary of the Invention

[0005] The embodiments of the present invention provide a GaN film grown on a Si substrate and a preparation method thereof, which can effectively improve the growth efficiency of the GaN film, enhance the growth quality of the GaN film, and improve the withstand voltage capability of power devices.

[0006] An embodiment of the present invention provides a GaN thin film grown on a Si substrate, comprising at least a Si substrate and a transition layer, a GaN buffer layer, a GaN channel layer, and a barrier layer epitaxially grown in sequence on the Si substrate;

[0007] The GaN buffer layer includes at least a first GaN layer, which is provided on a side of the transition layer away from the Si substrate, wherein the first GaN layer is configured as a stress retention layer epitaxially grown under a first condition; and

[0008] a second GaN layer, disposed on a side of the first GaN layer away from the transition layer, the second GaN layer being configured as a non-doped GaN high-resistance layer epitaxially grown under a second condition;

[0009] The GaN channel layer is configured as a non-doped GaN layer epitaxially grown under a third condition;

[0010] Wherein, the first condition at least includes a molar ratio of Group V to Group III raw materials not higher than 100.

[0011] Optionally, the molar ratio of the group V and group III raw materials is defined as a V / III ratio, the V / III ratio in the second condition is not less than the V / III ratio in the first condition, and the V / III ratio in the third condition is not less than the V / III ratio in the second condition.

[0012] Optionally, the first GaN layer is a fast layered growth layer, and the first condition further includes an average growth rate of not less than 8 μm / h.

[0013] Optionally, an average growth rate of the first GaN layer is higher than an average growth rate of the GaN channel layer.

[0014] Optionally, the thickness of the first GaN layer is in the range of 300-500 nm, and the thickness of the second GaN layer is in the range of 2-2.5 μm.

[0015] Optionally, the transition layer includes an AlN buffer layer and an Al x Ga (1-x) N buffer layer; the AlN buffer layer is grown on the Si substrate, the Al x Ga (1-x) The N buffer layer is grown between the AlN buffer layer and the first GaN layer; x Ga (1-x) The N buffer layer is configured as a step buffer layer with x gradually changing from 1 to 0, and / or Al x Ga (1-x) N and GaN alternating superlattice buffer layer.

[0016] Accordingly, an embodiment of the present invention further provides a method for preparing the GaN thin film grown on a Si substrate as described above. The preparation method comprises the following steps:

[0017] S1. Provide a Si substrate;

[0018] S2, growing a transition layer on the Si substrate;

[0019] S3, epitaxially growing a first GaN layer under a first condition on a side of the transition layer facing away from the Si substrate;

[0020] S4, epitaxially growing a second GaN layer on a side of the first GaN layer away from the transition layer under a second condition;

[0021] S5. epitaxially growing a GaN channel layer on a side of the second GaN layer facing away from the first GaN layer under a third condition;

[0022] S6. Growing a barrier layer on a side of the GaN channel layer away from the second GaN layer.

[0023] Optionally, the molar ratio of group V and group III raw materials is defined as V / III ratio, and the first condition in step S3 at least includes: maintaining the V / III ratio at 50-100; and the second condition in step S4 at least includes increasing the V / III ratio to 300-500.

[0024] Optionally, the first condition in step S3 further includes: maintaining an average growth rate of the first GaN layer (31) of not less than 8 μm / h; maintaining a growth temperature of 900-1100° C. and a reaction chamber pressure of 45-55 mbar, so as to deposit and form the first GaN layer (31) on the transition layer (20).

[0025] Optionally, the second condition in step S4 further includes maintaining an average growth rate of the second GaN layer (32) at 10-20 μm / h; maintaining a growth temperature at 900-1100° C. and a reaction chamber pressure at 45-55 mbar, so as to deposit and form the second GaN layer (32) on the first GaN layer (31).

[0026] Optionally, the flow rate of the Group III source gas introduced in step S3 is controlled to be 4000-6000 μmol / min; and the flow rate of the Group III source gas introduced in step S4 is controlled to be 4000-8000 μmol / min.

[0027] Optionally, the third condition in step S5 at least includes increasing the V / III ratio to 2000-5000 and reducing the average growth rate of the GaN channel layer (40) to 0.1-4 μm / h.

[0028] The embodiments of the present invention have the following beneficial effects: The embodiments of the present invention provide a GaN film grown on a Si substrate and a preparation method thereof. The GaN film grown on the Si substrate comprises at least a Si substrate and a transition layer, a GaN buffer layer, a GaN channel layer and a barrier layer epitaxially grown in sequence on the Si substrate. The GaN buffer layer comprises a first GaN layer and a second GaN layer, and the first GaN layer, the second GaN layer and the GaN channel layer are configured to be epitaxially grown under a first condition, a second condition and a third condition, respectively. The GaN film is deposited step by step, and the three-dimensional growth of GaN is suppressed by an extremely low V / III ratio at the initial stage of growth. A flat layered first GaN layer is rapidly grown as a stress-maintaining layer at the expense of the crystal quality of the film layer, so that sufficient structural compressive stress can be introduced at the first GaN layer to balance the subsequent thermal stress and improve the film layer's resistance to bending deformation. After quickly forming the first GaN layer, slightly increasing the V / III ratio and rapidly growing the high-impedance second GaN layer at a lower V / III ratio can effectively increase the C doping concentration, thereby substantially improving the voltage withstand capability of the GaN film and thus improving the overall voltage withstand effect of the power device.

[0029] In other words, the present application controls the growth orientation of the first GaN layer and the second GaN layer respectively with a low V / III ratio, and controls the first GaN layer and the second GaN layer to be deposited rapidly at an extremely high growth rate. In addition to improving the growth efficiency, the high growth rate combined with the low V / III ratio can also significantly increase the C doping concentration of the GaN film, increase the impedance, thereby improving the growth quality of the GaN film and improving the voltage resistance of the power device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A schematic structural diagram of a first embodiment of a GaN thin film grown on a Si substrate according to an embodiment of the present invention;

[0032] Figure 2 is a graph showing the relationship between C doping concentration and GaN growth rate;

[0033] Figure 3 A schematic structural diagram of a second embodiment of a GaN thin film grown on a Si substrate provided in an embodiment of the present invention;

[0034] The numbers in the figure represent:

[0035] Si substrate 10;

[0036] transition layer 20; AlN buffer layer 21; Al x Ga (1-x) N buffer layer 22;

[0037] GaN buffer layer 30; first GaN layer 31; second GaN layer 32;

[0038] GaN channel layer 40;

[0039] Barrier layer 50 . DETAILED DESCRIPTION

[0040] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, and are not exhaustive. Based on the embodiments of the present invention, all other embodiments derived by persons skilled in the art without inventive effort are within the scope of protection of the present invention. Furthermore, it should be understood that the specific embodiments described herein are intended only to illustrate and explain the present invention and are not intended to limit the present invention. In the present invention, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to upper and lower positions of the device in actual use or operation, specifically the directions of the drawings in the accompanying drawings. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed to indicate or imply relative importance or to implicitly specify the number of the technical features indicated. Therefore, features designated as "first," "second," etc. may explicitly or implicitly include one or more features. Furthermore, hereinafter and throughout this specification, the term "V / III ratio" refers to the molar ratio of the Group V to Group III raw materials.

[0041] The embodiments of the present invention provide a GaN film grown on a Si substrate and a preparation method thereof, which will be described in detail below. It should be understood that the description order of the following embodiments does not limit the preferred order of the embodiments of the present invention. In the following embodiments, the description of each embodiment has its own focus. For the part that is not described in detail in a certain embodiment, please refer to the relevant description of other embodiments. The embodiments of the present invention provide a GaN film grown on a Si substrate and a preparation method thereof, which are preferably implemented by MOCVD (metal organic chemical vapor deposition), and the equipment is preferably a planetary rotary MOCVD equipment.

[0042] The embodiment of the present invention provides a GaN film grown on a Si substrate. Figure 1As shown, the GaN thin film grown on the Si substrate includes a Si substrate 10 and a transition layer 20, a GaN buffer layer 30, a GaN channel layer 40, and a barrier layer 50 epitaxially grown on the Si substrate 10 from bottom to top. The GaN buffer layer 30 includes a first GaN layer 31 and a second GaN layer 32. The first GaN layer 31 is provided on the side of the transition layer 20 facing away from the Si substrate 10, and the second GaN layer 32 is provided on the side of the first GaN layer 31 facing away from the transition layer 20.

[0043] Specifically, the first GaN layer 31 in the embodiment of the present invention is configured as a stress-retaining layer epitaxially grown under a first condition, the second GaN layer 32 is configured as a non-doped GaN high-resistance layer epitaxially grown under a second condition, and the GaN channel layer 40 is configured as a non-doped GaN layer epitaxially grown under a third condition. Among them, the first condition needs to include at least a V / III ratio of not more than 100. Compared with the GaN film grown at a low speed using traditional processes, the first GaN layer 31 in this embodiment can be grown at a high speed under conditions of an extremely low V / III ratio (the average growth rate is generally not less than 8μm / h, which is higher than the average growth rate of the GaN channel layer 40), thereby effectively improving the growth efficiency of the GaN film and suppressing the growth orientation of the first GaN layer 31. Compared with the simultaneous existence of island and layered growth in traditional GaN thin film growth, the extremely low V / III ratio in this embodiment enhances the surface migration of Ga atoms, thereby inhibiting the layered growth of the first GaN layer 31, so that the first GaN layer 31 has a continuous, complete and relatively dense flat surface, thereby being able to greatly maintain the structural compressive stress of the entire film layer relative to the transition layer 20, so that more compressive stress can be used to balance the tensile stress generated by thermal mismatch during the cooling process, thereby improving the film layer's resistance to bending deformation.

[0044] Furthermore, the V / III ratio in the second condition is not less than the V / III ratio in the first condition, and the V / III ratio in the third condition is not less than the V / III ratio in the second condition. Figure 2As shown, under ideal conditions (excluding other influencing factors, from the perspective of data fitting), the C doping concentration is positively correlated with the square of the GaN growth rate. Therefore, the C doping concentration of the second GaN layer 32 can be increased by accelerating or maintaining a high growth rate of the second GaN layer 32, thereby increasing the impedance, substantially improving the voltage withstand capability of the GaN film, and thus improving the overall voltage withstand effect of the power device. In order to achieve a better C doping concentration, it is preferred that the average growth rate of the GaN buffer layer 30 is not less than 8μm / h. However, during actual growth, the film quality is negatively correlated with the growth rate. Unlimitedly increasing the film growth rate will cause the film quality to become very poor, which will in turn cause the risk of unreliable electrical properties of the film. In a preferred embodiment of the present invention, the average growth rate of the GaN buffer layer 30 is controlled to be 8-20μm / h. In particular, when differential growth is employed during the formation of the first GaN layer 31 and the second GaN layer 32, the overall performance of the GaN buffer layer 30 is improved significantly (including crystal quality, withstand voltage, etc.). Specifically, preferably, the second GaN layer 32 has a higher average growth rate than the first GaN layer 31, with a difference of 2-5 μm / h. The V / III ratio of the second GaN layer 32 contributes less to the C doping concentration, exhibiting an overall negative correlation (not shown). Maintaining a low V / III ratio during the growth of the second GaN layer 32 not only promotes the layered growth of the second GaN layer 32 but also improves the C doping concentration of the second GaN layer 32 to a certain extent. Furthermore, the process conditions for growth from the first GaN layer to the second GaN layer remain minimal, facilitating process control.

[0045] Furthermore, the third condition includes an average GaN growth rate of 0.1-4 μm / h. When growing the GaN channel layer, the growth rate is reduced and the V / III ratio is increased to improve the film quality. The V / III ratio is preferably 2000-5000.

[0046] Furthermore, the thickness of the first GaN layer 31 is preferably in the range of 300-500 nm to ensure that sufficient compressive stress can be introduced into the first GaN layer 31. The thickness of the second GaN layer 32 is preferably in the range of 2-2.5 μm to ensure the overall pressure resistance of the GaN film.

[0047] It can be understood that the present application controls the growth orientation of the first GaN layer 31 and the second GaN layer 32 respectively by a low V / III ratio, and controls the first GaN layer 31 and the second GaN layer 32 to be deposited rapidly at an extremely high growth rate, which can not only improve the growth efficiency of the GaN film, but also greatly increase the C doping concentration of the GaN film, thereby improving the growth quality of the GaN film and improving the voltage resistance of the power device. Obviously, the present application does not need to impose too many restrictions on the structure of the transition layer 20. In fact, the transition layer 20 in the embodiment of the present invention can be of various structures, for example, it can be a SiC (silicon carbide) pre-buffer layer, a low-temperature AlN (aluminum nitride) buffer layer, a high-temperature AlN buffer layer, an AlN nucleation layer and an Al x Ga (1-x) One or more common buffer layer structures such as a N (gallium aluminum nitride) buffer layer. Similarly, the epitaxial layer structure on the upper side of the GaN buffer layer 30 is not limited to the aforementioned GaN channel layer 40 and barrier layer 50, but may further include traditional epitaxial structures such as an AlN insertion layer, a GaN cap layer, and device layers (source, drain, gate, etc.), which are not listed in detail in this application. In addition, the third condition mentioned above can be a traditional GaN channel layer 40 growth condition, which is not excessively limited in this application.

[0048] In order to better illustrate the above embodiment, as an optional implementation method, Figure 3 As shown, the transition layer 20 in the embodiment of the present invention may include an AlN buffer layer 21 and an Al x Ga (1-x) N buffer layer 22. Among them, the AlN buffer layer 21 is grown on the Si substrate 10, which can avoid the degradation of the GaN film due to the reaction between Si and Ga, and inhibit the remelting of the Si substrate 10. In addition, the AlN buffer layer 21 can also alleviate the lattice mismatch problem between the Si substrate 10 and the overall film to a certain extent. x Ga (1-x) The N buffer layer 22 is grown between the AlN buffer layer 21 and the first GaN layer 31. x Ga (1-x) The lattice matching rate between the N buffer layer 22 and the AlN buffer layer 21 is relatively high, which can alleviate the lattice mismatch and thermal mismatch problems between the AlN buffer layer 21 and the first GaN layer 31 .

[0049] Al x Ga (1-x) The N buffer layer 22 may be a step buffer layer where x changes gradually from 1 to 0 (for example, x is 1.0, 0.8, 0.5, and 0.2 in sequence). x Ga (1-x) The number of N layers is at least two, and the Al composition x is higher. x Ga(1-x) N is close to the AlN buffer layer 21, and Al with a lower Al composition x x Ga (1-x) N is close to the first GaN layer 31 (i.e., the Al content decreases layer by layer toward the first GaN layer 31), so that the film layers between the AlN buffer layer 21 and the first GaN layer 31 have a high lattice adaptation rate. And / or, Al x Ga (1-x) The N buffer layer 22 can also be made of Al x Ga (1-x) The above embodiments are merely examples and do not limit the structure of the transition layer 20 in the embodiment of the present invention.

[0050] Accordingly, an embodiment of the present invention further provides a method for preparing the GaN thin film grown on a Si substrate as described above. The preparation method mainly comprises the following steps:

[0051] S1. Provide a Si substrate 10.

[0052] The Si substrate 10 has good thermal conductivity and high crystalline quality. Furthermore, the current preparation process for the Si substrate 10 is relatively mature, resulting in low production costs, which can reduce the manufacturing costs of power devices. Furthermore, before epitaxially growing other film layers on the Si substrate 10, the surface of the Si substrate 10 can be cleaned in advance to ensure the quality of the subsequent film layers.

[0053] S2. Growing a transition layer 20 on the Si substrate 10 (the orientation of the deposition surface of the Si substrate 10 is not limited).

[0054] Taking into account the serious lattice mismatch, thermal mismatch, and melt-back etching problems between the Si substrate 10 and the GaN film, in this embodiment, a transition layer 20 is grown on the Si substrate 10 as a buffer structure between the Si substrate 10 and the GaN film to alleviate the lattice mismatch and other problems between the Si substrate 10 and the GaN film, thereby ensuring the growth quality of the GaN film.

[0055] It is understandable that the transition layer 20 in this embodiment can be of various structures, such as a SiC pre-buffer layer, a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, an AlN nucleation layer, and an AlN buffer layer. x Ga (1-x) The embodiment does not impose too many restrictions on one or more common buffer layer structures such as N buffer layer.

[0056] As Figure 3 Taking one embodiment of the GaN film grown on the Si substrate as an example, in this embodiment, the transition layer 20 includes an AlN buffer layer 21 and an Al xGa (1-x) N buffer layer 22. AlN buffer layer 21 is grown on Si substrate 10 to improve the lattice adaptation of the entire film. x Ga (1-x) The N buffer layer 22 is grown between the AlN buffer layer 21 and the first GaN layer 31 to reduce the lattice mismatch and thermal mismatch between the AlN and GaN film layers. Accordingly, the above step S2 of growing the transition layer 20 on the Si substrate 10 may specifically include:

[0057] S2 - 1 . Growing an AlN buffer layer 21 on the Si substrate 10 .

[0058] As an example, a conventional AlN buffer layer 21 growth method may be employed: introducing NH3 pre-flow for 15 seconds, first growing a low-temperature AlN layer at 1020-1030°C, and then raising the temperature to 1120-1130°C to grow a high-temperature AlN layer, thereby forming the AlN buffer layer 21.

[0059] S2-2, growing Al on the AlN buffer layer 21 x Ga (1-x) N buffer layer 22 .

[0060] As an example, conventional Al x Ga (1-x) N buffer layer 22 growth method: For example, by step-grading method, three layers of Al are grown at a temperature of 1080-1090 ° C. x Ga (1-x) N film layer, where x can be 0.8, 0.5, 0.2, and decreases layer by layer in the direction away from the AlN buffer layer 21. Alternatively, the AlN film layer can be grown alternately at a temperature of 1040-1090 ° C by SLS. x Ga (1-x) N film layer and GaN film layer are alternated about 50-100 times to form Al with superlattice structure x Ga (1-x) N buffer layer 22. Of course, the Al can also be grown in a mixed manner of Step-Graded (step) and SLS (solid-liquid-solid) x Ga (1-x) The N buffer layer 22 is not described in detail here.

[0061] The above implementation is merely an example and does not limit the transition layer 20 in the embodiment of the present invention.

[0062] S3 . Epitaxially grow a first GaN layer 31 on the side of the transition layer 20 facing away from the Si substrate 10 under the first condition.

[0063] In this embodiment, when growing the first GaN layer 31, an extremely low V / III ratio (not higher than 100) is used to suppress the three-dimensional growth of GaN, and a continuous and flat first GaN layer 31 is rapidly grown at the expense of the crystal quality of the film layer, so that sufficient compressive stress can be introduced in the first GaN layer 31 to balance the subsequent thermal stress, thereby improving the film layer's resistance to bending deformation.

[0064] Furthermore, as a preferred embodiment, the process of step S3 can be specifically as follows: introducing source gas (such as TMGa, etc.) under the first conditions of a growth temperature of 900-1100°C, a reaction chamber pressure of 45-55mbar, and a V / III ratio of 50-100 to deposit and form a first GaN layer 31 on the transition layer 20.

[0065] S4 , epitaxially growing a second GaN layer 32 on a side of the first GaN layer 31 away from the transition layer 20 under a second condition.

[0066] In this embodiment, when growing the second GaN layer 32, it is necessary to appropriately increase the V / III ratio and rapidly grow the high-impedance second GaN layer 32 under the condition of a lower V / III ratio, which can effectively increase the C doping concentration, thereby substantially improving the voltage resistance of the GaN film, and further improving the overall voltage resistance effect of the power device.

[0067] Furthermore, as a preferred embodiment, the process of step S4 can be specifically as follows: maintaining the growth temperature at 900-1100°C and the reaction chamber pressure at 45-55 mbar, increasing the V / III ratio to 300-500, so as to deposit and form the second GaN layer 32 on the first GaN layer 31.

[0068] In addition, as some preferred embodiments, the source gas flow rate introduced in step S3 is preferably 4000-6000 μmol / min; the source gas flow rate introduced in step S4 is preferably 4000-8000 μmol / min to control the growth rate of GaN. It should be noted that this parameter is applicable to the more commonly used MOCVD equipment, such as Aixtron's G5, Taiyo Nippon Sanso's UR-25K, etc. In order to effectively increase the C doping concentration, the average growth rate of the first GaN layer 31 is preferably not less than 8 μm / h, and the average growth rate of the second GaN layer 32 is preferably 10-20 μm / h. The above embodiments are only some preferred schemes. The source gas flow rate can be fine-tuned according to the growth conditions of the first GaN layer 31 and the second GaN layer 32 to achieve the expected growth rate. Therefore, the source gas flow rate in the embodiments of the present invention is not specifically limited.

[0069] S5 . Epitaxially grow a GaN channel layer 40 on a side of the second GaN layer 32 facing away from the first GaN layer 31 under the third condition.

[0070] The GaN channel layer 40 can be epitaxially grown using conventional growth conditions. Undoped GaN can be used for the GaN channel layer 40, and a two-dimensional electron gas (2DEG) is formed between the GaN channel layer 40 and the subsequent barrier layer 50. To achieve optimal device performance, the third growth condition for the GaN channel layer 40 includes a growth rate significantly lower than that in the first growth condition and a V / III ratio significantly higher than that in the first growth condition. Preferably, the film growth rate in the third growth condition is 1 / 2 to 1 / 50 of the growth rate in the first growth condition, and the V / III ratio in the third growth condition is 20 to 100 times that in the first growth condition. Specifically, the third growth condition preferably includes an average GaN growth rate of 0.1 to 4 μm / h and a V / III ratio of 2000 to 5000 to improve film quality and increase the 2DEG concentration.

[0071] S6 , growing a barrier layer 50 on a side of the GaN channel layer 40 facing away from the second GaN layer 32 .

[0072] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present invention. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A GaN thin film grown on a Si substrate, comprising at least a Si substrate (10) and a transition layer (20), a GaN buffer layer (30), a GaN channel layer (40) and a barrier layer (50) epitaxially grown in sequence on the Si substrate (10), characterized in that: The GaN buffer layer (30) comprises at least a first GaN layer (31), which is provided on a side of the transition layer (20) facing away from the Si substrate (10), and the first GaN layer (31) is configured as a stress retention layer epitaxially grown under a first condition; as well as A second GaN layer (32) is provided on a side of the first GaN layer (31) away from the transition layer (20), and the second GaN layer (32) is configured as a non-doped GaN high-resistance layer epitaxially grown under a second condition; The GaN channel layer (40) is configured as a non-doped GaN layer epitaxially grown under a third condition; The first condition also includes an average growth rate of not less than 8 μm / h; The molar ratio of group V to group III raw materials is defined as a V / III ratio, wherein the first condition includes at least maintaining the V / III ratio at 50-100; and the second condition includes at least increasing the V / III ratio to 300-500; The second condition also includes maintaining an average growth rate of the second GaN layer (32) at 10-20 μm / h.

2. The GaN thin film grown on a Si substrate according to claim 1, wherein: The molar ratio of the Group V and Group III raw materials is defined as a V / III ratio, the V / III ratio in the second condition is not less than the V / III ratio in the first condition, and the V / III ratio in the third condition is not less than the V / III ratio in the second condition.

3. The GaN thin film grown on a Si substrate according to claim 1, wherein: The first GaN layer (31) is a fast layered growth layer.

4. The GaN thin film grown on a Si substrate according to claim 3, wherein: The average growth rate of the first GaN layer (31) is higher than the average growth rate of the GaN channel layer (40).

5. The GaN thin film grown on a Si substrate according to claim 1, wherein: The thickness of the first GaN layer (31) is in the range of 300-500 nm, and the thickness of the second GaN layer (32) is in the range of 2-2.5 μm.

6. The GaN thin film grown on a Si substrate according to any one of claims 1 to 5, characterized in that: The transition layer (20) includes an AlN buffer layer (21) and an Al x Ga (1-x) N buffer layer (22); the AlN buffer layer (21) is grown on the Si substrate (10), the Al x Ga (1-x) A N buffer layer (22) is grown between the AlN buffer layer (21) and the first GaN layer (31); the Al x Ga (1-x) The N buffer layer (22) is configured as a step buffer layer with x gradually changing from 1 to 0, and / or Al x Ga (1-x) N and GaN alternating superlattice buffer layer.

7. A method for preparing a GaN thin film grown on a Si substrate according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. providing a Si substrate (10); S2, growing a transition layer (20) on the Si substrate (10); S3, epitaxially growing a first GaN layer (31) under a first condition on a side of the transition layer (20) facing away from the Si substrate (10); S4, epitaxially growing a second GaN layer (32) on a side of the first GaN layer (31) facing away from the transition layer (20) under a second condition; S5. epitaxially growing a GaN channel layer (40) on a side of the second GaN layer (32) facing away from the first GaN layer (31) under a third condition; S6, growing a barrier layer (50) on a side of the GaN channel layer (40) facing away from the second GaN layer (32); The first condition in S3 further includes: maintaining an average growth rate of the first GaN layer (31) not less than 8 μm / h.

8. The method for preparing a GaN thin film grown on a Si substrate according to claim 7, wherein: The first condition in S3 further includes: maintaining a growth temperature of 900-1100° C. and a reaction chamber pressure of 45-55 mbar, so as to deposit and form the first GaN layer (31) on the transition layer (20).

9. The method for preparing a GaN thin film grown on a Si substrate according to claim 8, wherein: The growth temperature is maintained at 900-1100° C. and the reaction chamber pressure is maintained at 45-55 mbar to deposit and form the second GaN layer (32) on the first GaN layer (31).

10. The method for preparing a GaN thin film grown on a Si substrate according to claim 9, wherein: The flow rate of the Group III source gas introduced in S3 is controlled to be 4000-6000 μmol / min; the flow rate of the Group III source gas introduced in S4 is controlled to be 4000-8000 μmol / min.

11. The method for preparing a GaN thin film grown on a Si substrate according to claim 7, wherein: The molar ratio of group V and group III raw materials is defined as V / III ratio, and the third condition in S5 at least includes increasing the V / III ratio to 2000-5000 and reducing the average growth rate of the GaN channel layer (40) to 0.1-4 μm / h.

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