High-al component algan device structure and preparation method thereof

Abstract

The application discloses a high-Al-component AlGaN device structure and a preparation method thereof. The high-Al-component AlGaN device structure comprises a substrate with an inclination range of 0.7-2 degrees to a (001) plane, and a buffer layer, an AlGaN channel layer, a high-Al-component AlGaN barrier layer and a p-type AlGaN cap layer which are sequentially epitaxially grown. The surface roughness of the buffer layer is not more than 2 nm, the surface roughness of the AlGaN channel layer is less than 2 nm, and the p-type AlGaN cap layer has a macro-step superlattice structure. Thus, high hole concentration of the p-type AlGaN cap layer can be realized while avoiding interface scattering of the channel layer, threshold voltage is improved, and a high-Al-component AlGaN enhancement-mode HEMT device capable of working in a normally-off mode is obtained.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, specifically to a high-Al content AlGaN device structure and its fabrication method. Background Technology

[0002] High-aluminum (Al) AlGaN (aluminum gallium nitride) materials possess wide bandgap characteristics, demonstrating significant application prospects in high-temperature, high-voltage power devices. Compared to other ultra-wide bandgap semiconductor materials such as gallium oxide and diamond, a major advantage of AlGaN is its ability to simultaneously achieve n-type and p-type doping, thus forming homogeneous pn junctions. This means that homogeneous semiconductor thin films can be fabricated through a single epitaxial process, resulting in higher device reliability and stability under high-temperature and high-electric-field operating conditions. Currently, while gallium oxide is easily doped with n-type, p-type doping is extremely difficult, typically requiring the use of heterogeneous p-type nickel oxide; although diamond can achieve p-type conductivity through doping, effective n-type doping has not yet been reported. In contrast, AlGaN has an irreplaceable inherent advantage in constructing homogeneous pn structures.

[0003] However, high-Al composition AlGaN also faces the challenge of high activation energies in doping, making it difficult to increase carrier concentration. Furthermore, power devices typically require enhancement-mode (normally off) operation, meaning that the 2DEG (two-dimensional electron gas) in the channel region under the gate should be depleted when no external bias voltage is applied between the gate and drain, and the device can only be effectively turned on when a positive gate voltage is applied. Although high-Al composition AlGaN has p-type doping capability, achieving effective depletion of the channel 2DEG and increasing the threshold voltage in a thin p-type cap layer requires a sufficiently high hole concentration.

[0004] In practice, the Al content of the barrier layer of high Al content AlGaN devices is usually more than 0.6. If a GaN (gallium nitride) p-type layer is grown on it, the large lattice mismatch between the two will cause the huge compressive stress to make it difficult for GaN to maintain a two-dimensional growth mode. It is easy to exhibit island-like growth, resulting in deterioration of p-type material quality and a significant decrease in uniformity, making it difficult to stably deplete the under-gate channel.

[0005] Traditional p-type AlGaN materials also face challenges. While reducing the Al content lowers the hole activation energy, facilitating higher hole concentrations, the increased lattice mismatch between the lower Al content and the channel or barrier layer leads to increased compressive stress that can induce material relaxation with increasing thickness, resulting in quality degradation and problems similar to those encountered in p-GaN growth. Conversely, if p-type AlGaN with an Al content close to that of the channel or barrier layer is used, the hole activation energy in the conventional structure is as high as approximately 0.4 eV, with an activation rate of less than 1%. Furthermore, heavy doping can easily lead to a compensation effect, resulting in lower hole concentrations and further deterioration of material quality.

[0006] In summary, how to obtain a p-type cap layer with high hole concentration in high-Al composition AlGaN enhancement-mode HEMT (high electron mobility transistor) devices to achieve stable and reliable enhancement-mode operation has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address at least one of the aforementioned problems, the inventors conducted extensive research and experiments, discovering that when the tilt angle between the substrate and the (001) plane is in the range of 0.7° to 2°, the atomic steps can be effectively controlled. This allows the migration ability of Al atoms to be kept under control through growth conditions, preventing the formation of macrosteps due to excessively wide atomic steps and the formation of step aggregation due to excessively narrow atomic steps, thus avoiding difficulties in forming a smooth surface during epitaxy. Furthermore, since the substrate of this invention is a slanted substrate, it tends to result in a high surface roughness of the AlGaN channel layer. A high-roughness AlGaN channel layer increases interface scattering during 2DEG movement, which in turn makes it difficult to improve device performance. To avoid the problem of high surface roughness in the AlGaN channel layer, the inventors conducted extensive research and experiments, discovering that when the roughness of the buffer layer is controlled at a low level, the surface roughness of the AlGaN channel layer can also be controlled at a low level. Meanwhile, the inventors also discovered that when the p-type AlGaN cap layer has a macrostep superlattice structure, the p-type AlGaN cap layer can have a high hole concentration, thereby achieving effective depletion of the channel 2DEG and obtaining a stable high-Al-content AlGaN enhancement-mode HEMT device. Therefore, according to one aspect of the present invention, a high-Al-content AlGaN device structure is provided.

[0008] The high-Al composition AlGaN device structure includes a substrate with an inclination angle of 0.7° to 2° relative to the (001) plane; and a buffer layer, an AlGaN channel layer, a high-Al composition AlGaN barrier layer, and a p-type AlGaN cap layer epitaxially grown sequentially; wherein the surface roughness of the buffer layer does not exceed 2 nm; the surface roughness of the AlGaN channel layer is less than 2 nm; and the p-type AlGaN cap layer has a macrostep superlattice structure.

[0009] Therefore, while avoiding interface scattering in the channel layer, a high hole concentration in the p-type AlGaN cap layer can be achieved, thereby increasing the threshold voltage and obtaining a high-Al composition AlGaN enhancement-mode HEMT device that can operate normally off.

[0010] In some embodiments, the buffer layer comprises an AlN buffer layer and an AlGaN buffer layer epitaxially grown sequentially; the surface roughness of the AlN buffer layer does not exceed 1 nm; the surface roughness of the AlGaN buffer layer does not exceed 2 nm. The AlN buffer layer allows for the removal of impurities beneath the AlN buffer layer (the substrate or template layer grown on the substrate) during AlN buffer layer fabrication via surface purging or other methods. Furthermore, the surface roughness of the AlN buffer layer can be controlled to meet the growth conditions of the AlGaN buffer layer. When the substrate tilt angle is 0.7°, the width of the AlN unit sub-step is approximately 20 nm, and the width of the double-layer step is approximately 40 nm; when the substrate tilt angle is 2°, the width of the AlN unit sub-step is approximately 8 nm, and the width of the double-layer step is approximately 16 nm. Atomic steps within this width range have strong controllability, allowing for controlled migration of Al atoms through growth conditions, thus enabling control over the surface roughness of both the AlN and AlGaN buffer layers. Setting up an AlGaN buffer layer can alleviate the compressive strain caused by the large compositional difference between the AlGaN buffer layer and the AlGaN channel layer by using multiple AlGaN buffer layers with different Al compositions, thereby avoiding the problem of AlGaN channel layer degradation.

[0011] Since the buffer layer comprises sequentially epitaxially grown AlN and AlGaN buffer layers, a thicker AlGaN buffer layer is needed to release stress if the Al composition of the AlGaN channel layer is low. However, because the AlGaN buffer layer is grown on top of the AlN buffer layer, this heteroepitaxial growth causes the surface roughness of the AlGaN buffer layer to increase with increasing thickness (and stress). Therefore, it is necessary to control the Al composition of the AlGaN channel layer. In some embodiments, the Al composition of the AlGaN channel layer is required to be not less than 0.4 and not more than 0.8.

[0012] Although the hole activation energy of a uniformly doped p-type AlGaN cap layer in a bulk material with an Al composition below 0.2 is approximately 0.2 eV, which is higher than that of a GaN cap layer, a higher overall hole surface concentration can be achieved by increasing the thickness of the p-type AlGaN cap layer, thereby achieving channel depletion. For example, in AlGaN, a 2DEG surface concentration of 1 × 10⁻⁶ eV can be achieved. 13 cm -2 Under these conditions, if the hole concentration of the p-type AlGaN cap layer is 5 × 10⁻⁶ 17 cm -3Therefore, at least 200nm is needed to achieve hole depletion. However, when the Al composition of the AlGaN channel layer is above 0.4, in order to reduce the huge mismatch stress caused by the thick p-type AlGaN cap layer, the Al composition of the p-type AlGaN cap layer also needs to be increased accordingly. However, increasing the Al composition of the p-type AlGaN cap layer will significantly increase the activation energy, resulting in a significant decrease in hole concentration. That is, the relationship between increasing Al composition and increasing hole concentration is negatively correlated. Meanwhile, due to the severe alloy scattering of AlGaN, the carrier mobility is relatively low. To achieve a high conduction current, a high concentration of 2DEG is required. This necessitates a high concentration of holes in the p-type AlGaN cap layer, resulting in a thickness of the p-type AlGaN cap layer far exceeding 500 nm. However, an excessively thick p-type AlGaN cap layer not only presents significant growth challenges and severe epitaxial quality degradation, but also makes it difficult to effectively deplete the channel (due to the relatively low hole mobility). Therefore, the thickness of the p-type AlGaN cap layer that effectively depletes the channel cannot be too thick. To this end, the inventors discovered that when the p-type AlGaN cap layer has a macrostep superlattice structure, the p-type AlGaN cap layer can have a high hole concentration, thereby achieving effective depletion of the channel 2DEG. Moreover, when the p-type AlGaN cap layer includes periodically alternating high-Al composition AlGaN layers and low-Al composition AlGaN layers, and the thickness of both high-Al composition AlGaN layers and low-Al composition AlGaN layers does not exceed 4 nm, and the Al composition difference between the high-Al composition AlGaN layers and low-Al composition AlGaN layers is greater than 0.2, it can maintain the p-type AlGaN cap layer in a strained state, better facilitate the effective tunneling of excited holes, and control the thickness of the p-type AlGaN cap layer from becoming too thick. At the same time, since the inventors also discovered that Ga in AlGaN has stronger migration ability, and the Ga composition in the low-Al composition AlGaN layer is higher, growing the low-Al composition AlGaN layer on the high-Al composition AlGaN barrier layer can make the Ga migration ability stronger and more likely to form a conditionally non-uniform distribution of Al and Ga composition in the plane. Therefore, in some embodiments, the p-type AlGaN cap layer includes periodically alternating high-Al composition AlGaN layers and low-Al composition AlGaN layers; the thickness of both the high-Al composition AlGaN layers and the low-Al composition AlGaN layers does not exceed 4 nm; the Al composition difference between the high-Al composition AlGaN layers and the low-Al composition AlGaN layers is greater than 0.2, and the low-Al composition AlGaN layers are grown on the high-Al composition AlGaN barrier layer. The number of periods of the high-Al composition AlGaN layers and the low-Al composition AlGaN layers can be adjusted according to the required forward threshold voltage range.

[0013] In some preferred embodiments, the Al composition difference between the high-Al-content AlGaN layer and the low-Al-content AlGaN layer is greater than 0.3. This allows the p-type AlGaN cap layer to maintain a stable strain state.

[0014] Since the growth of the AlGaN channel layer and the high-Al content AlGaN barrier layer is continuous, normal growth methods struggle to create a steep interface between them, leading to severe 2DEG interface scattering. To address this issue, the inventors conceived of introducing an insertion layer between the AlGaN channel layer and the high-Al content AlGaN barrier layer to form a steep interface. Furthermore, a high concentration of 2DEG is required to achieve high conduction current. To solve these problems, the inventors conducted extensive research and experiments, discovering that the extremely strong spontaneous polarization effect of AlN (aluminum nitride) can induce a high-density two-dimensional electron gas (2DEG) at the high-Al content channel interface, ensuring excellent carrier transport capabilities. Therefore, according to one aspect of the invention, an AlN insertion layer is provided between the AlGaN channel layer and the high-Al content AlGaN barrier layer, with the thickness of the AlN insertion layer controlled to not exceed 3 nm. Therefore, the confinement effect of 2DEG can be deteriorated due to the flattening of the energy band of the barrier layer caused by the excessive thickness of the insertion layer. This invention introduces an AlN insertion layer with a thickness of no more than 3 nm between the AlGaN channel layer and the high Al composition AlGaN barrier layer, which enables the device to have a high 2DEG concentration, thereby improving the device's operating performance.

[0015] Since the substrate of the high-Al-content AlGaN device structure of this invention is a slanted substrate, the inventors discovered during the fabrication of the high-Al-content AlGaN device structure that although a controllable macrostep morphology can be obtained by growing AlN and AlGaN in a high-temperature quasi-equilibrium state on a slanted substrate, this macrostep morphology leads to AlGaN exhibiting a low Al content at the step edges and a high Al content at the mesa. While this macrostep AlGaN structure, combined with superlattice doping, can achieve Al content exceeding 1×10⁻⁶ under high Al content conditions, it is not feasible to obtain AlGaN with a superlattice doping profile. 18 cm -3The device exhibits extremely high hole concentration. However, the channel morphology of the macrosteps introduces interface scattering; moreover, the significant Al composition fluctuations in the macrostep channels greatly increase alloy scattering, limiting device performance. To address these issues, the inventors conducted extensive research and experiments, discovering that introducing non-equilibrium growth on an inclined substrate allows for two-dimensional growth of the AlGaN barrier layer and preceding epitaxial films, resulting in a low-roughness surface. Subsequently, p-type AlGaN cap layers are grown in a quasi-equilibrium state, maintaining the superlattice structure of the p-type AlGaN cap layer while forming macrosteps on it. The resulting device structure achieves high current performance and stable enhancement-mode drive. Therefore, according to another aspect of the present invention, a method for fabricating a high-Al-content AlGaN device structure is provided.

[0016] In the fabrication method of the high-Al composition AlGaN device structure, a buffer layer, an AlGaN channel layer, and a high-Al composition AlGaN barrier layer are sequentially grown on the substrate by non-equilibrium growth, and the surface roughness of the buffer layer is controlled to be no more than 2 nm, and the surface roughness of the AlGaN channel layer is less than 2 nm. Then, a p-type AlGaN cap layer is grown on the high-Al composition AlGaN barrier layer by quasi-equilibrium growth, so that the p-type AlGaN cap layer has a macrostep superlattice structure.

[0017] Due to the unique properties of AlN, significant step aggregation effects easily occur under high-temperature growth conditions. When the buffer layer includes an AlN buffer layer, conventional AlN buffer layer fabrication methods result in high surface roughness of the AlN buffer layer, which in turn leads to high surface roughness of the AlGaN channel layer. Ultimately, this increases interface scattering during 2DEG movement, degrading the performance of power devices. To address these issues, the inventors conducted extensive research and experiments. Initially, they used high temperatures to fabricate the AlN buffer layer, as high temperatures are theoretically required for high-quality AlN epitaxial growth. However, after testing, they found that the AlN buffer layer fabricated at high temperatures exhibited high surface roughness and macrosteps. Analysis revealed that the poor surface roughness of the high-temperature grown AlN buffer layer was primarily due to the oblique substrate. When the AlN buffer layer was fabricated at high temperatures, it grew closer to an equilibrium state, making it more prone to macrostep formation under oblique substrate conditions. Therefore, the inventors conceived of using a low-temperature, high 5:3 ratio and high growth rate (non-equilibrium high-speed growth) process to prepare the AlN buffer layer, in order to fabricate a smooth, two-dimensionally grown AlN buffer layer on an inclined substrate. For example, in this method for fabricating a high-Al-content AlGaN device structure, when preparing the AlN buffer layer, the reaction chamber temperature does not exceed 1200°C, the reaction chamber pressure is 50 mbar to 100 mbar, the 5:3 ratio is greater than 500, and the AlN growth rate is greater than 1.5 μm / h. In some embodiments, the 5:3 ratio during AlN buffer layer preparation is the molar ratio of ammonia to trimethylaluminum.

[0018] In some embodiments, to ensure a low surface roughness of the prepared AlGaN buffer layer, a low-temperature, high 5:3 ratio, and high growth rate process are employed during AlGaN buffer layer fabrication. For example, in this method for fabricating a high-Al-content AlGaN device structure, the reaction chamber temperature is no higher than 1080°C, the reaction chamber pressure is 75 mbar to 150 mbar, the 5:3 ratio is greater than 1500, and the AlGaN growth rate is greater than 2 μm / h. In some embodiments, the 5:3 ratio during AlGaN buffer layer fabrication is the molar ratio of ammonia to trimethylaluminum + trimethylgallium.

[0019] In some embodiments, to ensure a low surface roughness of the prepared AlGaN channel layer, a low-temperature and high 5:3 ratio process is used during AlGaN channel layer preparation. Furthermore, the inventors have found that when the growth rate of the AlGaN channel layer is too fast, not only does the increased Al source flow rate lead to increased pre-reaction of the Al source, resulting in numerous impurity defects in the epitaxial layer, but also, at high growth rates, Al atoms hardly migrate, leading to increased Al composition fluctuations. The resulting poor uniformity of the Al composition in the channel layer causes severe 2DEG scattering. Therefore, it is necessary to control the growth rate of the channel layer to prevent it from becoming too high. In some embodiments, during AlGaN channel layer preparation, the reaction chamber temperature does not exceed 1050°C, the reaction chamber pressure is 75 mbar to 150 mbar, the 5:3 ratio is greater than 1500, and the AlGaN growth rate is between 1 μm / h and 2 μm / h (0.3 nm / s to 0.6 nm / s). In some embodiments, the 5:3 ratio during AlGaN channel layer preparation is the molar ratio of ammonia to trimethylaluminum + trimethylgallium.

[0020] In some embodiments, to achieve a stable 2DEG surface concentration distribution, a low-temperature, high 5:3 ratio process is used when preparing the high-Al composition AlGaN barrier layer. Since the high-Al composition AlGaN barrier layer has a higher Al content, the growth rate of the high-Al composition AlGaN barrier layer needs to be strictly controlled to ensure a uniform distribution of Al and Ga components. This avoids problems such as insufficient Al atom migration, increased Al composition fluctuations, and poor thickness uniformity caused by excessively rapid growth, thereby improving the current performance and consistency of the device. In some embodiments, when preparing the high-Al composition AlGaN barrier layer, the reaction chamber temperature does not exceed 1050℃, the reaction chamber pressure is 75mbar~150mbar, the 5:3 ratio is greater than 2000, and the AlGaN growth rate is between 0.7μm / h and 1.4μm / h (0.2nm / s~0.4nm / s). In some embodiments, the 5:3 ratio used in preparing the high-Al composition AlGaN barrier layer is the molar ratio of ammonia to trimethylaluminum + trimethylgallium.

[0021] In some embodiments, to ensure a steep interface between the AlN insertion layer and the high-Al content AlGaN barrier layer, a low growth rate is required to maintain stable surface morphology. Therefore, during AlN insertion layer preparation, the reaction chamber pressure is maintained at 50-100 mbar (the reaction chamber temperature and pressure can be consistent with those used during AlGaN channel layer preparation), the 5:3 ratio is controlled to be greater than 2000, and the AlN growth rate is kept below 0.1 nm / s. This prevents a significant increase in the 5:3 ratio due to Ga source shutdown during AlN insertion layer preparation (which can be achieved by rapidly switching the ammonia bypass), which could lead to unstable AlN insertion layer quality. In some embodiments, the 5:3 ratio during AlN insertion layer preparation is the molar ratio of ammonia to trimethylaluminum.

[0022] In some embodiments, when preparing the p-type AlGaN cap layer, the reaction chamber temperature is higher than 1050°C, the reaction chamber pressure is 50 mbar to 133 mbar, the 5:3 ratio is less than 500, and the Al source is introduced first, followed by the Ga source and ammonia.

[0023] In some embodiments, to achieve a steep interface of the superlattice and a non-uniform distribution of Al composition in the macrosteps, the growth process needs to be interrupted after the preparation of both high-Al-composed and low-Al-composed AlGaN layers. This is achieved through a pulsed growth method. For example, after preparing a low-Al-composed AlGaN layer, the Al source, Ga source, and ammonia gas are interrupted; or a small amount of Ga source (less than one-tenth of the epitaxial flux) and ammonia gas are introduced during Al source preparation (to avoid excessive Ga desorption leading to abnormally high Al composition at the interface), and growth is stopped. This ensures effective Al atom migration and achieves a near-equilibrium macrostep structure. Since the tilt angle between the substrate and the (001) plane of this invention ranges from 0.7° to 2°, it ensures strong controllability of the atomic steps, and the controlled step height and width can match the migration length of Al atoms in the p-type AlGaN cap layer prepared at temperatures above 1050°C (the migration length range is determined to be 10 nm to 30 nm based on the Al composition range and growth conditions).

[0024] In some embodiments, the growth of the substrate to the high-Al composition AlGaN barrier layer is a continuous growth (all growth conditions [temperature, pressure, group III source, group V source] are gradually and continuously changed within 240s [optionally 180s, 120s, 60s, etc.]) to avoid problems such as the desorption and migration of Ga atoms with strong migration ability due to interruption of the organic source, and morphological changes caused by the migration of surface Al atoms; and after the AlGaN channel layer is prepared, the Ga source is turned off, and during the growth time of the AlN insertion layer, the conditions such as Al source, Ga source, ammonia, temperature and pressure are gradually changed to the growth conditions of the high-Al composition AlGaN barrier layer until the AlN insertion layer is grown. Then, the Ga source is turned on to grow the high-Al composition AlGaN barrier layer. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a high-Al composition AlGaN device according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a high-Al composition AlGaN device according to another embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a high-Al composition AlGaN device according to another embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a high-Al composition AlGaN device according to another embodiment of the present invention; Figure 5 A schematic diagram of AFM (atomic force microscope) obtained after thermal annealing of an AlN template layer sputtered on an inclined substrate, which is a method for fabricating a high Al composition AlGaN device structure according to an embodiment of the present invention; Figure 6 A schematic diagram of AFM showing the high-alkalinity AlGaN device structure fabrication method according to an embodiment of the present invention, where an AlN buffer layer is grown at high speed on an inclined substrate. Figure 7 A schematic diagram of AFM for low-speed growth of AlN buffer layers on an inclined substrate; Figure 8 This is an AFM schematic diagram of the low-speed growth of a p-type AlGaN cap layer in a method for fabricating a high-Al composition AlGaN device structure according to an embodiment of the present invention. Figure 9 This is a schematic diagram of the Hall parameter testing structure of the p-type AlGaN device structure with high Al composition prepared in Example 3 of the present invention. Reference numerals: 11, Substrate; 12, Template layer; 13, Buffer layer; 131, AlN buffer layer; 132, AlGaN buffer layer; 14, AlGaN channel layer; 15, Insertion layer; 16, High Al composition AlGaN barrier layer; 17, p-type AlGaN cap layer; 171, Low Al composition AlGaN layer; 172, High Al composition AlGaN layer. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0027] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising" or "including" include not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The terminology used herein is generally that commonly used by those skilled in the art; in case of any discrepancy with commonly used terminology, the terminology used herein shall prevail.

[0028] In this invention, the term "5 / 3 ratio," also known as the V / III ratio, refers to the molar ratio of group 5 sources to group 3 sources.

[0029] Furthermore, for ease of description, spatial relative terms such as “below,” “under,” “lower,” “above,” and “upper” may be used herein to describe the relationship between one element or component and another (or other) element or component as shown in the figure. In addition to the orientation shown in the figure, spatial relative terms are intended to include different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptors used herein can be interpreted accordingly.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Figure 1The diagram schematically illustrates a high-Al composition AlGaN device structure according to a first embodiment of the present invention.

[0032] like Figure 1 As shown, the high Al composition AlGaN device structure includes a substrate with an inclination angle of 0.7° to 2° relative to the (001) plane; and a buffer layer, an AlGaN channel layer, a high Al composition AlGaN barrier layer, and a p-type AlGaN cap layer epitaxially grown sequentially; wherein, the surface roughness of the buffer layer does not exceed 2 nm; the surface roughness of the AlGaN channel layer is less than 2 nm; the p-type AlGaN cap layer has a macrostep superlattice structure; and the substrate is made of AlN.

[0033] Since the present invention sets the tilt angle between the substrate and the (001) surface in the range of 0.7° to 2°, it can ensure that the atomic steps have a strong controllability. Thus, the migration ability of Al atoms can be controlled by controlling the growth conditions. The atomic steps will not be too wide to generate step aggregation and form macro steps, nor will the atomic steps be too narrow to generate step aggregation too easily, making it difficult to form a smooth surface during epitaxy.

[0034] In some preferred embodiments, such as Figure 1 As shown, the buffer layer includes an AlN buffer layer and an AlGaN buffer layer grown epitaxially in sequence; the surface roughness of the AlN buffer layer does not exceed 1 nm; the surface roughness of the AlGaN buffer layer does not exceed 2 nm.

[0035] In some preferred embodiments, the thickness of the buffer layer ranges from 1 μm to 3 μm.

[0036] In some preferred embodiments, the Al composition of the AlGaN channel layer is required to be not less than 0.4 and not more than 0.8.

[0037] In some preferred embodiments, the thickness of the AlGaN channel layer ranges from 200 nm to 400 nm.

[0038] In some preferred embodiments, the surface roughness of the high-Al content AlGaN barrier layer does not exceed 2 nm to obtain a 2DEG with better uniformity. Preferably, the Al content in the high-Al content AlGaN barrier layer is uniformly distributed to obtain a 2DEG with better uniformity.

[0039] In some preferred embodiments, the thickness of the high-Al composition AlGaN barrier layer ranges from 15 nm to 35 nm.

[0040] In some preferred embodiments, such as Figure 1As shown, the p-type AlGaN cap layer includes periodically alternating high-Al-content AlGaN layers and low-Al-content AlGaN layers; the thickness of both the high-Al-content AlGaN layers and the low-Al-content AlGaN layers does not exceed 4 nm; the Al-content difference between the high-Al-content AlGaN layers and the low-Al-content AlGaN layers is greater than 0.2; and the low-Al-content AlGaN layer is grown on the high-Al-content AlGaN barrier layer. More preferably, the Al-content of the low-Al-content AlGaN layer is 0.2 to 0.5 lower than the Al-content AlGaN barrier layer, to avoid excessive strain between the low-Al-content AlGaN layer and the high-Al-content AlGaN barrier layer due to the large difference in Al-content, which could lead to relaxation phenomena when the low-Al-content AlGaN layer exceeds the critical thickness (p-type layers are generally composed of superlattices with a thickness of less than 4 nm).

[0041] In some preferred embodiments, the thickness of the p-type AlGaN cap layer ranges from 50 nm to 200 nm.

[0042] In some preferred embodiments, the Al content of the high Al content AlGaN barrier layer is 0.15 to 0.35 higher than that of the AlGaN channel layer.

[0043] Figure 2 The diagram schematically illustrates a high-Al composition AlGaN device structure according to a second embodiment of the present invention.

[0044] The main difference between this embodiment and the first embodiment is that: Figure 2 As shown, the high-Al composition AlGaN device structure also includes an insertion layer, which is disposed between the AlGaN channel layer and the high-Al composition AlGaN barrier layer. The material of the insertion layer is AlN.

[0045] In some preferred embodiments, the thickness of the insertion layer does not exceed 3 nm.

[0046] Figure 3 The diagram schematically illustrates a high-Al composition AlGaN device structure according to a third embodiment of the present invention.

[0047] The main difference between this embodiment and the first embodiment is that the substrate is made of sapphire or SiC (silicon carbide), preferably sapphire, and a template layer is provided between the substrate and the buffer layer, the template layer being made of AlN.

[0048] Figure 4 The diagram schematically illustrates a high-Al composition AlGaN device structure according to a fourth embodiment of the present invention.

[0049] The main difference between this embodiment and the second embodiment is that the substrate can be made of sapphire or SiC (silicon carbide), preferably sapphire, and a template layer is provided between the substrate and the buffer layer, the template layer being made of AlN.

[0050] In the high-Al composition AlGaN device structures of the third and fourth embodiments, sapphire is preferred as the substrate material because the cost of sapphire substrates is lower than that of SiC and AlN substrates. In particular, the substrate in this patent is a beveled substrate (with an angle). Sapphire, due to its long single-crystal rod, is easier to fabricate into beveled substrates. In contrast, SiC and AlN substrates have relatively thin wafers, resulting in significant wafer waste during bevel cutting, leading to a substantial increase in cost and hindering low-cost commercialization. In some preferred embodiments, the thickness of the AlN template layer is not less than 300 nm and does not exceed 2 μm to avoid insufficient dislocation interactions due to an excessively thin template layer, which could compromise crystal quality. It also avoids introducing excessive stress due to an excessively thick template layer, which could cause wafer warping.

[0051] According to one aspect of the present invention, a method for fabricating a high-Al-content AlGaN device structure according to a first embodiment is provided.

[0052] In this method for fabricating a high-Al composition AlGaN device structure, a buffer layer, an AlGaN channel layer, and a high-Al composition AlGaN barrier layer are sequentially grown on a substrate using a non-equilibrium growth method, while controlling the surface roughness of the buffer layer to be no more than 2 nm and the surface roughness of the AlGaN channel layer to be less than 2 nm. Then, a p-type AlGaN cap layer is grown on the high-Al composition AlGaN barrier layer using a quasi-equilibrium growth method, so that the p-type AlGaN cap layer has a macrostep superlattice structure.

[0053] Since the buffer layer, AlGaN channel layer, and high-Al content AlGaN barrier layer are grown in a non-equilibrium manner, the buffer layer and AlGaN channel layer can be guaranteed to have low surface roughness, thereby reducing interface scattering during 2DEG movement. Furthermore, by growing a p-type AlGaN cap layer on the high-Al content AlGaN barrier layer through a quasi-equilibrium growth method, the p-type AlGaN cap layer can have a macrostep superlattice structure, resulting in a high hole concentration. This enables effective depletion of the channel 2DEG, leading to a stable high-Al content AlGaN enhancement-mode HEMT device.

[0054] In some preferred embodiments, the growth of the substrate to the high-Al-content AlGaN barrier layer is continuous. In this method for fabricating the high-Al-content AlGaN device structure, when fabricating the AlN buffer layer, the reaction chamber temperature is no higher than 1200°C, the reaction chamber pressure is 50 mbar to 100 mbar, the molar ratio of ammonia to trimethylaluminum is greater than 500, and the AlN growth rate is greater than 1.5 μm / h; when fabricating the AlGaN buffer layer, the reaction chamber temperature is no higher than 1080°C, the reaction chamber pressure is 75 mbar to 150 mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is greater than 1500, and the AlGaN growth rate is greater than 2 μm / h. When fabricating the AlGaN channel layer, the reaction chamber temperature is no higher than 1050°C, the reaction chamber pressure is 75 mbar to 150 mbar, the 5 / 3 ratio is greater than 1500, and the AlGaN growth rate is between 1 μm / h and 2 μm / h. When preparing a high-Al content AlGaN barrier layer, the reaction chamber temperature should not exceed 1050℃, the reaction chamber pressure should be 75mbar~150mbar, the 5:3 ratio should be greater than 2000, and the AlGaN growth rate should be between 0.7μm / h and 1.4μm / h.

[0055] In some preferred embodiments, when preparing the p-type AlGaN cap layer, the reaction chamber temperature is higher than 1050°C, the reaction chamber pressure is 50 mbar to 133 mbar, the 5:3 ratio is less than 500, and the Al source is introduced first, followed by the Ga source and ammonia. After preparing the low-Al-content AlGaN layer, the Al source, Ga source, and ammonia are interrupted to stop growth; or after preparing the low-Al-content AlGaN layer, a small amount of Ga source and ammonia are introduced when introducing the Al source (to avoid excessive Ga desorption leading to abnormally high Al content at the interface), and growth is stopped. In some specific embodiments, after the AlGaN barrier layer is grown, a small amount of trimethylaluminum is introduced first (at the same flow rate as the subsequently introduced trimethylaluminum) for 4 seconds (without trimethylgallium); then, trimethylaluminum and trimethylgallium are introduced simultaneously for 40 seconds. TMA / F TMG =2, F is an abbreviation for flow rate; then, turn off trimethylaluminum and trimethylgallium, and purge for several seconds to tens of seconds (depending on the growth thickness and flow rate; for example, the larger the growth thickness and the higher the flow rate, the longer the purging time), and the superlattice AlGaN potential well (low Al composition AlGaN layer) is grown; then, turn on trimethylaluminum again (flow rate is the same as the subsequent trimethylaluminum flow rate), for 4 seconds, then simultaneously turn on trimethylaluminum and trimethylgallium, for 40 seconds, F TMA / F TMG=3; then, turn off trimethylaluminum and trimethylgallium, purge for several seconds to tens of seconds, and the superlattice AlGaN barrier (high Al composition AlGaN) or superlattice AlGaN well (low Al composition AlGaN) is grown. This method of pre-introducing Al atoms before AlN (or AlGaN) growth is an Al migration-enhanced growth method. Preferably, the low Al composition AlGaN layer grown on the AlGaN barrier layer needs to use this Al migration-enhanced growth method; of course, both the low Al composition AlGaN layer and the high Al composition AlGaN layer can use this Al migration-enhanced growth method; the AlGaN barrier layer can also use this Al migration-enhanced growth method. In some embodiments, when using the aforementioned Al migration-enhanced growth method, ammonia gas can also be introduced by reducing the flow rate or periodically interrupting the gas supply, such as not introducing ammonia gas when only TMA is introduced, and introducing ammonia gas at other times, or intermittently alternating the gas supply. This ensures that Al atoms can migrate effectively and obtain a macrostep structure in a near-equilibrium growth state.

[0056] In some preferred embodiments, the reaction chamber temperature is 1050℃~1100℃ when preparing the p-type AlGaN cap layer.

[0057] In some preferred embodiments, when preparing the p-type AlGaN cap layer, the p-type doped impurity is a Mg compound material, such as Mg2Mg.

[0058] According to one aspect of the present invention, a method for fabricating a high-Al-content AlGaN device structure according to a second embodiment is provided.

[0059] The difference between the fabrication method of the high-Al content AlGaN device structure in this embodiment and the first fabrication method of the high-Al content AlGaN device structure is that it also includes the following method: After the AlGaN channel layer is prepared, the Ga source is turned off, and during the growth time of the AlN insertion layer, the conditions such as Al source, Ga source, ammonia, temperature and pressure are gradually changed to the growth conditions of the high Al content AlGaN barrier layer until the AlN insertion layer is grown. Then, the Ga source is turned on to grow the high Al content AlGaN barrier layer to avoid problems such as the desorption and migration of Ga atoms with strong migration ability due to the interruption of the organic source, and morphological changes caused by the migration of surface Al atoms.

[0060] In some preferred embodiments, when preparing the AlN insertion layer, the 5:3 ratio is greater than 2000, and the AlN growth rate is below 0.1 nm / s.

[0061] According to one aspect of the present invention, a method for fabricating a high-Al-content AlGaN device structure according to a third or fourth embodiment is provided.

[0062] The difference between the fabrication method of the high-Al content AlGaN device structure in this embodiment and the fabrication method of the first or second high-Al content AlGaN device structure is that it further includes the following method: The AlN template layer is obtained by sputtering on the substrate followed by ultra-high temperature (1650℃~1750℃) annealing, or by direct epitaxial growth on the substrate using MOCVD (metal-organic chemical vapor deposition). Preferably, it is obtained by sputtering on the substrate followed by ultra-high temperature annealing to achieve a higher crystal quality AlN template layer, thereby reducing leakage channels and making it easier to suppress leakage under high-field conditions.

[0063] The following specific examples illustrate the fabrication method of AlGaN device structures with high Al content.

[0064] Example 1 In the first step, when preparing an AlN buffer layer on an AlN substrate with an inclination angle of 1° to the (001) plane, the reaction chamber temperature is 1150℃, the reaction chamber pressure is 75mbar, the molar ratio of ammonia to trimethylaluminum is 800, and the AlN growth rate is 2μm / h, so as to prepare an AlN buffer layer with a surface roughness of no more than 1nm.

[0065] In the second step, when preparing the AlGaN buffer layer on the AlN buffer layer, the reaction chamber temperature is 1050℃, the reaction chamber pressure is 100mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 2000, and the AlGaN growth rate is 3μm / h, so as to prepare an AlGaN buffer layer with a surface roughness of no more than 2nm.

[0066] In the third step, when preparing the AlGaN channel layer on the AlGaN buffer layer, the reaction chamber temperature is 1000℃, the reaction chamber pressure is 100mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 2000, and the AlGaN growth rate is 1.5μm / h, so as to prepare an AlGaN channel layer with a surface roughness of less than 2nm and an Al composition of 0.4.

[0067] In the fourth step, when preparing a high-Al content AlGaN barrier layer on the AlGaN channel layer, the reaction chamber temperature is 1000℃, the reaction chamber pressure is 100mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 3000, and the AlGaN growth rate is between 1.0μm / h.

[0068] Step 5: A p-type AlGaN cap layer is fabricated on the high-Al content AlGaN barrier layer. The reaction chamber temperature is 1080℃, the reaction chamber pressure is 100 mbar, and the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 400. The Al source is introduced first, followed by the Ga source and ammonia. After fabricating the low-Al content AlGaN layer, the Al source, Ga source, and ammonia are interrupted to stop growth, thus fabricating a p-type AlGaN cap layer with a periodically alternating high-Al content AlGaN layer and a low-Al content AlGaN layer. The low-Al content AlGaN layer is grown on the macrostep superlattice structure of the high-Al content AlGaN barrier layer (e.g., a p-type AlGaN cap layer). Figure 8 (As shown).

[0069] Furthermore, the growth of the substrate to the high-Al composition AlGaN barrier layer is a continuous growth.

[0070] Example 2 The difference between this embodiment and Embodiment 1 is that: After step three and before step four, the following steps are also included: After the AlGaN channel layer is prepared, the Ga source is turned off, and during the growth time of the AlN insertion layer, the conditions such as Al source, Ga source, ammonia, temperature and pressure are gradually changed to the growth conditions of the high Al content AlGaN barrier layer until the AlN insertion layer is grown. Then, the Ga source is turned on to grow the high Al content AlGaN barrier layer. When preparing the AlN insertion layer, the reaction chamber pressure is 100 mbar, the molar ratio of ammonia to trimethylaluminum is controlled at 2000, and the AlN growth rate is below 0.1 nm / s, so as to set an AlN insertion layer with a thickness of no more than 3 nm between the AlGaN channel layer and the high Al content AlGaN barrier layer.

[0071] Example 3 The difference between this embodiment and Embodiment 1 is that: The first step is to prepare an AlN template layer on a sapphire substrate with an inclination angle of 1° to the (001) plane. The AlN template layer is obtained by sputtering on the substrate followed by ultra-high temperature annealing. Then, an AlN buffer layer is prepared on the AlN template layer. When preparing the AlN buffer layer, the reaction chamber temperature is 1150℃, the reaction chamber pressure is 75mbar, the molar ratio of ammonia to trimethylaluminum is 800, and the AlN growth rate is 2μm / h, so as to prepare an AlN buffer layer with a surface roughness of no more than 1nm and a thickness of 1μm.

[0072] Step 5: Fabrication of a p-type AlGaN cap layer on the high-Al content AlGaN barrier layer: After the high-Al content AlGaN barrier layer is grown, trimethylaluminum (without ammonia) is first introduced for pre-laying aluminum. Then, at a reaction chamber temperature of 1100℃ and a reaction chamber pressure of 100mbar, a superlattice low-Al content AlGaN layer is grown by introducing trimethylaluminum, trimethylgallium, and ammonia, with a molar ratio of ammonia to trimethylaluminum + trimethylgallium of 400. Next, the Al and Ga sources are interrupted to stop growth, and only ammonia is introduced for purging. Then, trimethylaluminum is introduced again. Aluminum (without ammonia) is used for pre-laying; then trimethylaluminum, trimethylgallium, and ammonia are introduced to grow a superlattice high-Al composition AlGaN layer; then the Al and Ga sources are interrupted to stop growth, and only ammonia is introduced for purging; superlattice low-Al composition AlGaN layers and superlattice high-Al composition AlGaN layers are grown alternately to prepare a p-type AlGaN cap layer with a macrostep superlattice structure of periodically alternating high-Al composition AlGaN layers and low-Al composition AlGaN layers, and low-Al composition AlGaN layers grown on a high-Al composition AlGaN barrier layer.

[0073] The AFM image of the annealed AlN template layer prepared in this embodiment is shown below. Figure 5 As shown, according to Figure 5 As can be seen, the AlN template layer prepared in this embodiment has a smooth surface after annealing.

[0074] The AFM image of the AlN buffer layer prepared in this embodiment is as follows: Figure 6 As shown, according to Figure 6 It can be seen that the AlN buffer layer prepared in this embodiment has a highly flat surface morphology with a roughness of less than 1 nm, which is significantly better than the surface roughness of AlN buffer layers grown at low speed on tilted substrates using existing techniques (such as...). Figure 7 The roughness (as shown) is based on Figure 7 It can be seen that the existing technology grows AlN buffer layers at low speed on tilted substrates, resulting in surfaces with obvious macrosteps.

[0075] The AFM image of the p-type AlGaN cap layer prepared in this embodiment is as follows: Figure 8 As shown, according to Figure 8 It can be seen that the p-type AlGaN cap layer prepared in this embodiment has a distinct macrostep surface.

[0076] like Figure 9 As shown, the hole concentration of the p-type AlGaN cap layer prepared in this embodiment exceeds 1×10⁻⁶. 18 cm -3 .

[0077] Example 4 The difference between this embodiment and Embodiment 2 is as follows: The first step is to prepare an AlN template layer on a sapphire substrate with an inclination angle of 1° to the (001) plane. The AlN template layer is obtained by sputtering on the substrate followed by ultra-high temperature annealing. Then, an AlN buffer layer is prepared on the AlN template layer. When preparing the AlN buffer layer, the reaction chamber temperature is 1200℃, the reaction chamber pressure is 75mbar, the molar ratio of ammonia to trimethylaluminum is 800, and the AlN growth rate is 2μm / h, so as to prepare an AlN buffer layer with a surface roughness of no more than 1nm and a thickness of 1.5μm.

[0078] The fifth step involves preparing a p-type AlGaN cap layer on the high-Al content AlGaN barrier layer: After the high-Al content AlGaN barrier layer is grown, trimethylaluminum (without ammonia) is first introduced for pre-laying aluminum. Then, at a reaction chamber temperature of 1100℃ and a reaction chamber pressure of 100mbar, a superlattice low-Al content AlGaN layer is grown by introducing trimethylaluminum, trimethylgallium, and ammonia. The molar ratio of ammonia to trimethylaluminum + trimethylgallium is 400. The Al source is introduced first, followed by the Ga source and ammonia. Then, the Al source is interrupted, growth is stopped, and ammonia and a Ga source with a flow rate of one-tenth of the epitaxial growth flow rate are introduced for purging. Then, the superlattice high-Al content AlGaN and low-Al content AlGaN layers are grown periodically under quasi-equilibrium growth conditions to prepare a p-type AlGaN cap layer with a macrostep superlattice structure of periodically alternating high-Al content AlGaN layers and low-Al content AlGaN layers, and low-Al content AlGaN layers grown on the high-Al content AlGaN barrier layer.

[0079] Example 5 In the first step, when preparing an AlN buffer layer on an AlN substrate with an inclination angle of 0.7° to the (001) plane, the reaction chamber temperature is 1100℃, the reaction chamber pressure is 50mbar, the molar ratio of ammonia to trimethylaluminum is 500, and the AlN growth rate is 1.5μm / h, so as to prepare an AlN buffer layer with a surface roughness of no more than 1nm.

[0080] In the second step, when preparing the AlGaN buffer layer on the AlN buffer layer, the reaction chamber temperature is 1030℃, the reaction chamber pressure is 75mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 1500, and the AlGaN growth rate is 2μm / h, so as to prepare an AlGaN buffer layer with a surface roughness of no more than 2nm.

[0081] In the third step, when preparing the AlGaN channel layer on the AlGaN buffer layer, the reaction chamber temperature is 1000℃, the reaction chamber pressure is 75mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 1500, and the AlGaN growth rate is 1μm / h, so as to prepare an AlGaN channel layer with a surface roughness of less than 2nm and an Al composition of 0.6.

[0082] In the fourth step, when preparing a high-Al content AlGaN barrier layer on the AlGaN channel layer, the reaction chamber temperature was 1000℃, the reaction chamber pressure was 75mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium was 2000, and the AlGaN growth rate was 0.7μm / h.

[0083] The fifth step involves preparing a p-type AlGaN cap layer on the high-Al content AlGaN barrier layer. The reaction chamber temperature is 1080℃, the reaction chamber pressure is 50mbar, and the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 300. The Al source is introduced first, followed by the Ga source and ammonia. After preparing the low-Al content AlGaN layer, the Al source, Ga source, and ammonia are interrupted to stop the growth. This process prepares a p-type AlGaN cap layer with a periodically alternating high-Al content AlGaN layer and a low-Al content AlGaN layer, and the low-Al content AlGaN layer is grown on the macrostep superlattice structure of the high-Al content AlGaN barrier layer.

[0084] Furthermore, the growth of the substrate to the high-Al composition AlGaN barrier layer is a continuous growth.

[0085] Example 6 In the first step, when preparing an AlN buffer layer on an AlN substrate with an inclination angle of 2° to the (001) plane, the reaction chamber temperature is 1200℃, the reaction chamber pressure is 100mbar, the molar ratio of ammonia to trimethylaluminum is 1000, and the AlN growth rate is 3μm / h, so as to prepare an AlN buffer layer with a surface roughness of no more than 1nm.

[0086] In the second step, when preparing the AlGaN buffer layer on the AlN buffer layer, the reaction chamber temperature is 1080℃, the reaction chamber pressure is 150mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 3000, and the AlGaN growth rate is 4μm / h, so as to prepare an AlGaN buffer layer with a surface roughness of no more than 2nm.

[0087] In the third step, when preparing the AlGaN channel layer on the AlGaN buffer layer, the reaction chamber temperature is 1050℃, the reaction chamber pressure is 150mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 3000, and the AlGaN growth rate is 2μm / h, so as to prepare an AlGaN channel layer with a surface roughness of less than 2nm and an Al composition of 0.8.

[0088] In the fourth step, when preparing a high-Al content AlGaN barrier layer on the AlGaN channel layer, the reaction chamber temperature was 1050℃, the reaction chamber pressure was 150mbar, the molar ratio of ammonia to trimethylaluminum + trimethylgallium was 3000, and the AlGaN growth rate was 1.4μm / h.

[0089] The fifth step involves preparing a p-type AlGaN cap layer on the high-Al content AlGaN barrier layer. The reaction chamber temperature is 1100℃, the reaction chamber pressure is 133mbar, and the molar ratio of ammonia to trimethylaluminum + trimethylgallium is 500. The Al source is introduced first, followed by the Ga source and ammonia. After preparing the low-Al content AlGaN layer, the Al source, Ga source, and ammonia are interrupted to stop the growth, thereby preparing a p-type AlGaN cap layer with a periodically alternating high-Al content AlGaN layer and a low-Al content AlGaN layer, and the low-Al content AlGaN layer growing on the macrostep superlattice structure of the high-Al content AlGaN barrier layer.

[0090] Furthermore, the growth of the substrate to the high-Al composition AlGaN barrier layer is a continuous growth.

[0091] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A high-Al content AlGaN device structure, characterized in that, include: The substrate has an angle of inclination to the (001) plane ranging from 0.7° to 2°. And sequentially epitaxially grown buffer layer, AlGaN channel layer, high-Al composition AlGaN barrier layer, and p-type AlGaN cap layer; wherein, The surface roughness of the buffer layer does not exceed 2 nm; The surface roughness of the AlGaN channel layer is less than 2 nm; The p-type AlGaN cap layer has a macrostep superlattice structure.

2. The high Al content AlGaN device structure according to claim 1, characterized in that, The buffer layer comprises an AlN buffer layer and an AlGaN buffer layer grown epitaxially in sequence; The surface roughness of the AlN buffer layer does not exceed 1 nm; The surface roughness of the AlGaN buffer layer does not exceed 2 nm.

3. The high Al content AlGaN device structure according to claim 2, characterized in that, The Al composition of the AlGaN channel layer is required to be no less than 0.4 and no more than 0.

8.

4. The high Al content AlGaN device structure according to claim 3, characterized in that, The p-type AlGaN cap layer includes periodically alternating high-Al content AlGaN layers and low-Al content AlGaN layers; The thickness of both the high-Al content AlGaN layer and the low-Al content AlGaN layer does not exceed 4 nm. The difference in Al composition between the high-Al-content AlGaN layer and the low-Al-content AlGaN layer is greater than 0.2; Furthermore, the low-Al composition AlGaN layer is grown on the high-Al composition AlGaN barrier layer.

5. The high-Al composition AlGaN device structure according to any one of claims 1 to 4, characterized in that, An AlN insertion layer is disposed between the AlGaN channel layer and the high-Al composition AlGaN barrier layer; The thickness of the AlN insertion layer does not exceed 3 nm.

6. The method for fabricating a high-Al content AlGaN device structure according to any one of claims 1 to 5, characterized in that, A buffer layer, an AlGaN channel layer, and a high-Al composition AlGaN barrier layer are sequentially grown on a substrate using a non-equilibrium growth method, and the surface roughness of the buffer layer is controlled to be no more than 2 nm, while the surface roughness of the AlGaN channel layer is less than 2 nm. Then, a p-type AlGaN cap layer is grown on the high Al composition AlGaN barrier layer by a quasi-equilibrium growth method, so that the p-type AlGaN cap layer has a macrostep superlattice structure.

7. The method for fabricating the high-Al content AlGaN device structure according to claim 6, characterized in that, When preparing the AlN buffer layer, the reaction chamber temperature is not higher than 1200℃, the reaction chamber pressure is 50mbar~100mbar, the 5:3 ratio is greater than 500, and the AlN growth rate is greater than 1.5μm / h; When preparing the AlGaN buffer layer, the reaction chamber temperature is not higher than 1080℃, the reaction chamber pressure is 75mbar~150mbar, the 5:3 ratio is greater than 1500, and the AlGaN growth rate is greater than 2μm / h. When preparing the AlGaN channel layer, the reaction chamber temperature is not higher than 1050℃, the reaction chamber pressure is 75mbar~150mbar, the 5:3 ratio is greater than 1500, and the AlGaN growth rate is between 1μm / h and 2μm / h. When preparing the high-Al content AlGaN barrier layer, the reaction chamber temperature is not higher than 1050℃, the reaction chamber pressure is 75mbar~150mbar, the 5:3 ratio is greater than 2000, and the AlGaN growth rate is between 0.7μm / h and 1.4μm / h.

8. The method for fabricating a high-Al content AlGaN device structure according to claim 6, characterized in that, When preparing the AlN insertion layer, the reaction chamber pressure is 50 mbar to 100 mbar, the 5:3 ratio is greater than 2000, and the AlN growth rate is below 0.1 nm / s.

9. The method for fabricating a high-Al content AlGaN device structure according to claim 6, characterized in that, When preparing p-type AlGaN capping layers, the reaction chamber temperature is higher than 1050℃, the reaction chamber pressure is 50mbar~133mbar, the 5:3 ratio is less than 500, and the Al source is introduced first, followed by the Ga source and ammonia. After preparing both low-Al content AlGaN layers and high-Al content AlGaN layers, the Al source, Ga source, and ammonia gas were interrupted, and growth was stopped.

10. The method for fabricating a high-Al content AlGaN device structure according to any one of claims 6 to 9, characterized in that, The growth of the substrate to the high-Al composition AlGaN barrier layer is a continuous growth; After the AlGaN channel layer is prepared, the Ga source is turned off, and during the growth time of the AlN insertion layer, the conditions such as Al source, Ga source, ammonia, temperature and pressure are gradually changed to the growth conditions of the high Al content AlGaN barrier layer until the AlN insertion layer is grown. Then, the Ga source is turned on to grow the high Al content AlGaN barrier layer.

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