Heterojunction back-barrier gan hemt epitaxial structure and preparation method, and device

Abstract

The application discloses a heterojunction back barrier GaN HEMT epitaxial structure and a preparation method and a device thereof, relates to the technical field of semiconductor devices, and comprises a substrate layer, a nucleation layer arranged on the substrate layer, a GaN buffer layer arranged on the nucleation layer, a composite back barrier layer arranged on the GaN buffer layer, a GaN channel layer arranged on the composite back barrier layer, and an AlGaN barrier layer arranged on the GaN channel layer; the composite back barrier layer comprises a beta-Ga2O3 layer arranged on the GaN buffer layer and an AlGaN layer arranged on the beta-Ga2O3 layer. The heterojunction back barrier GaN HEMT epitaxial structure introduces the composite back barrier layer, uses the non-polarization characteristic of the beta-Ga2O3 layer to eliminate the parasitic channel at the interface between the AlGaN and the GaN buffer layer, simultaneously uses the AlGaN layer to improve the conduction band at the interface between the AlGaN and the GaN channel layer, suppresses the source-drain leakage current, and improves the breakdown voltage of the device.

Description

Technical Field

[0001] This application relates to the field of semiconductor device technology, and more specifically, to a heterojunction back barrier GaN HEMT epitaxial structure, its fabrication method, and the device thereof. Background Technology

[0002] Gallium nitride high electron mobility transistors (GaN HEMTs) have shown great potential in high-voltage, high-power, and high-frequency applications due to their excellent wide bandgap characteristics. However, in the off-state, traditional AlGaN / GaN HEMT devices suffer from drain-induced barrier lowering (DIBL) caused by high drain voltage, leading to significant leakage current in the GaN buffer layer. This buffer layer leakage problem severely restricts the device's breakdown voltage capability, becoming a key bottleneck limiting its performance and reliability in high-voltage scenarios. To address this issue, the industry commonly employs a method of introducing a single layer of AlGaN back barrier below the channel layer, utilizing its higher barrier to limit electron leakage to the buffer layer. However, due to the polarization effect between AlGaN and GaN, this approach causes the energy band at the AlGaN / GaN heterojunction to bend downwards, forming a parasitic channel. Under high voltage, this parasitic channel leads to punch-through leakage between the source and drain, limiting further improvements in the device's breakdown voltage.

[0003] In recent years, gallium oxide (β-Ga2O3) has attracted attention as an ultrawide bandgap semiconductor material. Its absence of spontaneous polarization and piezoelectric polarization effects causes the bandgap at the β-Ga2O3 / GaN heterojunction to bend upwards, theoretically preventing the formation of parasitic conductive channels. Simultaneously, its bandgap, far exceeding that of GaN, provides a higher electronic barrier, offering stronger confinement of channel carriers and potentially increasing channel electron concentration while suppressing leakage current. However, when using β-Ga2O3 alone as the back barrier, although it avoids parasitic channel problems at the GaN buffer layer interface, the conduction band may decrease at the heterojunction with the upper GaN channel layer due to bandgap mismatch, weakening the confinement effect on channel carriers and affecting further optimization of device on-resistance. Summary of the Invention

[0004] The purpose of this application is to provide a heterojunction back barrier GaN HEMT epitaxial structure, fabrication method, and device. By introducing a composite back barrier layer, the parasitic channel at the interface between AlGaN and GaN buffer layer is eliminated by utilizing the non-polarization characteristics of the β-Ga2O3 layer. At the same time, the conduction band at the interface between the AlGaN layer and the GaN channel layer is enhanced by utilizing the AlGaN layer, thereby suppressing drain-source leakage current and improving the device breakdown voltage.

[0005] The embodiments of this application are implemented as follows: A first aspect of this application provides a heterojunction back barrier GaN HEMT epitaxial structure, including a substrate layer, a nucleation layer disposed on the substrate layer, a GaN buffer layer disposed on the nucleation layer, a composite back barrier layer disposed on the GaN buffer layer, a GaN channel layer disposed on the composite back barrier layer, and an AlGaN barrier layer disposed on the GaN channel layer; wherein the composite back barrier layer includes a β-Ga2O3 layer disposed on the GaN buffer layer and an AlGaN layer disposed on the β-Ga2O3 layer.

[0006] As one possible implementation, the substrate layer is made of Si, Al2O3, SiC, or GaN.

[0007] In one possible implementation, the thickness of the β-Ga2O3 layer is 5-50 nm, and the thickness of the AlGaN layer is 10-100 nm.

[0008] As one possible implementation, the resistivity of the GaN buffer layer is greater than 1×10⁻⁶. 9 Ω˙cm.

[0009] As one possible implementation, a p-GaN layer and / or a GaN cap layer are also disposed on the AlGaN barrier layer.

[0010] A second aspect of this application provides a method for fabricating a heterojunction back-barrier GaN HEMT epitaxial structure, used to fabricate the aforementioned heterojunction back-barrier GaN HEMT epitaxial structure, the method comprising: A core layer and a GaN buffer layer are sequentially grown on the substrate; A composite back barrier layer is grown on the GaN buffer layer, the composite back barrier layer comprising a β-Ga2O3 layer and an AlGaN layer grown sequentially. A GaN channel layer and an AlGaN barrier layer are sequentially grown on the composite back barrier layer.

[0011] As one possible implementation, the sequential growth of a nucleation layer and a GaN buffer layer on the substrate includes: A nucleation layer and a GaN buffer layer were sequentially grown on the substrate using MOCVD technology.

[0012] As one possible implementation, growing a composite back barrier layer on the GaN buffer layer includes: A β-Ga2O3 layer and an AlGaN layer are sequentially grown on the GaN buffer layer using MOCVD or MBE processes.

[0013] As one possible implementation, the sequential growth of a GaN channel layer and an AlGaN barrier layer on the composite back barrier layer includes: A GaN channel layer and an AlGaN barrier layer were sequentially grown on the composite back barrier layer using the MOCVD process.

[0014] A third aspect of this application provides a heterojunction back barrier GaN HEMT device, including the above-described heterojunction back barrier GaN HEMT epitaxial structure, wherein a source, a gate, and a drain are disposed on the epitaxial structure.

[0015] The beneficial effects of the embodiments of this application include: The heterojunction back barrier GaN HEMT epitaxial structure includes a substrate layer, a nucleation layer disposed on the substrate layer, a GaN buffer layer disposed on the nucleation layer, a composite back barrier layer disposed on the GaN buffer layer, a GaN channel layer disposed on the composite back barrier layer, and an AlGaN barrier layer disposed on the GaN channel layer; wherein, the composite back barrier layer includes a β-Ga2O3 layer disposed on the GaN buffer layer and an AlGaN layer disposed on the β-Ga2O3 layer. By introducing a composite back barrier layer and leveraging the significant difference between the non-polarized characteristics of β-Ga2O3 and the polarization characteristics of AlGaN and GaN, the heterojunction band structure is synergistically designed, achieving the following significant improvements in overall performance: First, due to the non-polarized characteristics of β-Ga2O3, the parasitic conductive channels caused by polarization effects in the traditional monolayer AlGaN back barrier are effectively eliminated. This design fundamentally avoids punch-through leakage of parasitic channels under high voltage, significantly reducing off-state leakage current and thus substantially improving the device's breakdown voltage. Second, the conduction band at the interface between the AlGaN layer and the upper GaN channel layer is enhanced, suppressing electron overflow from the channel to the buffer layer and preventing current carrying capacity issues caused by poor band matching between the monolayer β-Ga2O3 back barrier and the GaN channel layer. The first aspect addresses the problem of insufficient carrier confinement. Secondly, the β-Ga2O3 and AlGaN layers form a "bandgap," with the two materials working in tandem. The β-Ga2O3 layer suppresses the underlying parasitic channel, while the AlGaN layer reduces carrier overflow to the buffer layer, achieving the dual goals of "no parasitic channel + strong carrier confinement," which cannot be achieved simultaneously with a single-layer β-Ga2O3 back barrier. Thirdly, through bandgap modulation of the GaN / β-Ga2O3 / AlGaN / GaN heterojunction back barrier, the two key characteristics of "high barrier" and "no parasitic channel" are simultaneously achieved in the same epitaxial structure. This not only resolves the contradiction between breakdown voltage and on-resistance in traditional single-layer AlGaN back barrier and single-layer β-Ga2O3 schemes, but also provides a basis for high-voltage, high-power GaN... HEMT devices offer a reliable, integrable, and controllable fabrication technology path. Fifthly, this epitaxial structure can be grown stepwise using conventional epitaxial processes such as MOCVD and MBE, without the need for complex doping or subsequent processing, facilitating integration with existing GaN device process platforms and exhibiting good process compatibility and scalability. In summary, the epitaxial structure provided in this application achieves synergistic innovation in material selection, bandgap design, and structural integration, providing an effective technical solution for the development of high-performance, high-reliability GaN-based power devices. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the heterojunction back barrier GaN HEMT epitaxial structure provided in an embodiment of this application; Figure 2 This is a schematic diagram illustrating the fabrication process of the heterojunction back barrier GaN HEMT epitaxial structure provided in the embodiments of this application; Figure 3 A comparison diagram of the energy bands of a heterojunction back barrier, a monolayer AlGaN back barrier, a monolayer β-Ga2O3 back barrier, and a GaN HEMT device without a back barrier, provided for embodiments of this application. Figure 4 This is a current distribution diagram of a heterojunction back barrier GaN HEMT device during breakdown, provided in an embodiment of this application. Figure 5 The current distribution diagram of a single-layer AlGaN back-barrier GaN HEMT device during breakdown is provided for the embodiments of this application; Figure 6 A comparison of breakdown voltages between a heterojunction back-barrier GaN HEMT device and a monolayer AlGaN back-barrier GaNHEMT device provided in the embodiments of this application.

[0018] Icons: 1-Substrate layer; 2-Nucleation layer; 3-GaN buffer layer; 4-β-Ga2O3 layer; 5-AlGaN layer; 6-GaN channel layer; 7-AlGaN barrier layer; 8-Source; 9-Gate; 10-Drain. Detailed Implementation

[0019] The embodiments described below represent the information necessary for those skilled in the art to practice the embodiments and illustrate the best mode for practicing the embodiments. After reading the following description with reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and will recognize the application of these concepts not specifically set forth herein. It should be understood that these concepts and applications fall within the scope of this disclosure and the appended claims.

[0020] It should be understood that when an element (such as a layer, region, or substrate) is referred to as "on another element" or "extending to another element," it may be directly on another element or directly extending to another element, or there may be an intermediate element. Similarly, it should be understood that when an element (such as a layer, region, or substrate) is referred to as "on another element" or "extending over another element," it may be directly on another element or directly extending to another element, or there may be an intermediate element.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that, when used herein, the term “comprising” indicates the presence of the stated feature, integer, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups of the foregoing.

[0022] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that the terms used herein should be interpreted as having the same meaning as they would in the context of this specification and the relevant field, and not in an idealized or overly formal sense, unless expressly defined herein.

[0023] Gallium nitride high electron mobility transistors (GaN HEMTs) possess excellent wide bandgap characteristics, making them suitable for high-voltage, high-power, and high-frequency applications. However, their traditional structures are prone to leakage in the GaN buffer layer during turn-off due to high drain voltage, limiting the improvement of breakdown voltage. While the commonly used monolayer AlGaN back barrier scheme can improve the barrier, the formation of parasitic channels at the interface due to polarization effects cannot completely solve the leakage problem. In recent years, gallium oxide (β-Ga2O3) has attracted attention as a non-polarized, ultra-wide bandgap material. The heterojunction between β-Ga2O3 and GaN bends the band upwards, avoiding parasitic channels and providing a higher electron barrier, which is beneficial for suppressing leakage and increasing channel electron concentration. However, when using β-Ga2O3 alone as a back barrier, although it can avoid parasitic channels at the interface with the GaN buffer layer, the conduction band may decrease at the heterojunction with the upper GaN channel layer due to band mismatch in the material system. This weakens the confinement effect on channel carriers, affecting further optimization of the device's on-resistance.

[0024] To solve the above problems, please refer to the following: Figure 1 and Figure 2This application provides a heterojunction back barrier GaNHEMT epitaxial structure, its fabrication method, and the device. By introducing a composite back barrier layer and utilizing the non-polarized characteristics of β-Ga2O3 and the significant difference in polarization characteristics between AlGaN and GaN, the heterojunction band structure is synergistically designed, achieving the following significant improvements in overall performance: Firstly, due to the non-polarized characteristics of the β-Ga2O3 layer 4, the parasitic conductive channel caused by polarization effect in the traditional single-layer AlGaN back barrier is effectively eliminated. This design fundamentally avoids the punch-through leakage of parasitic channels under high voltage, significantly reducing the off-state leakage current, thereby substantially improving the breakdown voltage of the device. Secondly, the conduction band at the interface between the AlGaN layer 5 and the upper GaN channel layer 6 is enhanced, suppressing the leakage of electrons from the channel to the buffer layer, and avoiding the leakage of electrons from the single-layer β-Ga2O3 back barrier due to polarization effect with GaN. The problem of insufficient carrier confinement caused by poor band matching in the N-channel layer 6 is addressed. Thirdly, the β-Ga2O3 layer 4 and AlGaN layer 5 form a "band ladder," with the two layers working in tandem. The β-Ga2O3 layer 4 suppresses the underlying parasitic channel, while the AlGaN layer 5 reduces carrier overflow to the buffer layer, achieving the dual goals of "no parasitic channel + strong carrier confinement," which cannot be achieved simultaneously with a single-layer β-Ga2O3 back barrier. Fourthly, through band modulation of the GaN / β-Ga2O3 / AlGaN / GaN heterojunction back barrier, the two key characteristics of "high barrier" and "no parasitic channel" are simultaneously achieved in the same epitaxial structure. This not only solves the contradiction between breakdown voltage and on-resistance in traditional single-layer AlGaN back barrier and single-layer β-Ga2O3 schemes, but also provides a basis for high-voltage, high-power GaN... HEMT devices offer a reliable, integrable, and controllable fabrication technology path. Fifthly, this epitaxial structure can be grown stepwise using conventional epitaxial processes such as MOCVD and MBE, without the need for complex doping or subsequent processing, facilitating integration with existing GaN device process platforms and exhibiting good process compatibility and scalability. In summary, the epitaxial structure provided in this application achieves synergistic innovation in material selection, bandgap design, and structural integration, providing an effective technical solution for the development of high-performance, high-reliability GaN-based power devices.

[0025] Specifically, such as Figures 1 to 2 As shown, in a first aspect of this application, a heterojunction back barrier GaNHEMT epitaxial structure is provided, including a substrate layer 1, a nucleation layer 2 disposed on the substrate layer 1, a GaN buffer layer 3 disposed on the nucleation layer 2, a composite back barrier layer disposed on the GaN buffer layer 3, a GaN channel layer 6 disposed on the composite back barrier layer, and an AlGaN barrier layer 7 disposed on the GaN channel layer 6; wherein, the composite back barrier layer includes a β-Ga2O3 layer 4 disposed on the GaN buffer layer 3 and an AlGaN layer 5 disposed on the β-Ga2O3 layer 4.

[0026] It should be noted that the epitaxial structure includes a substrate layer 1 and a nucleation layer 2, a GaN buffer layer 3, a composite back barrier layer, a GaN channel layer 6, and an AlGaN barrier layer 7 stacked on the substrate layer 1. The substrate layer 1 serves as the supporting substrate for the entire epitaxial structure, providing a stable physical carrier for the subsequent growth of each functional layer. Its material must meet the lattice matching and thermal stability requirements for epitaxial growth. The nucleation layer 2 is located between the substrate layer 1 and the GaN buffer layer 3. Its core function is to alleviate the lattice mismatch and thermal expansion coefficient difference between the substrate material and the GaN material, reduce the defect density, and lay the foundation for the high-quality growth of the GaN buffer layer 3. The GaN buffer layer 3 mainly functions to isolate substrate impurity diffusion and support the upper structure. The composite back barrier layer is located between the GaN buffer layer 3 and the GaN channel layer 6 and is crucial for realizing the heterojunction back barrier. The β-G The a2O3 layer 4 has no spontaneous polarization or piezoelectric polarization effects, and its band gap (approximately 4.8 eV) is much larger than that of GaN, which can suppress the parasitic channel below. The AlGaN layer 5 utilizes its polarization difference with GaN to enhance the conduction band above. The two layers work together to achieve band modulation and leakage current suppression. The GaN channel layer 6 serves as a transport channel for charge carriers (electrons). GaN material itself has high electron mobility characteristics, which can significantly reduce charge carrier transport losses compared to the β-Ga2O3 channel scheme, ensuring high conductivity of the device. The AlGaN barrier layer 7 and the upper GaN channel layer 6 form a traditional AlGaN / GaN heterojunction. The polarization difference between the two induces a high concentration of two-dimensional electron gas (2DEG) at the interface, further enhancing the accumulation of charge carriers in the channel, while providing a structural basis for the subsequent device electrode fabrication (such as source 8, gate 9, and drain 10).

[0027] Traditional single-layer AlGaN back barrier suffers from downward bending of the interface band due to the polarization effect between AlGaN and GaN, forming parasitic conductive channels. This leads to punch-through leakage under high voltage, failing to fundamentally solve the problem of buffer layer leakage. However, in this application, the non-polarized characteristics of β-Ga2O3 are utilized to completely eliminate the conditions for the formation of parasitic conductive channels, blocking the punch-through leakage path of the buffer layer at its source. This significantly reduces the device's off-state leakage current and substantially improves the breakdown voltage. The improved breakdown voltage breaks through the performance bottleneck of traditional GaN HEMT devices in high-voltage applications (such as power electronic converters and high-voltage power supplies), enabling the device to adapt to higher voltage levels and expanding the application range of GaN-based devices. At the same time, the reduction in leakage current decreases the device's off-state power consumption and improves energy utilization efficiency.

[0028] Meanwhile, the polarization difference between AlGaN layer 5 and the upper GaN channel layer 6 forms a stable electron potential well at the interface, promoting efficient accumulation of charge carriers in GaN channel layer 6 and significantly increasing the two-dimensional electron gas concentration. The synergistic effect of the two layers achieves a balance between "parasitic-free channel" and "high charge carrier concentration." The high electron mobility of GaN channel layer 6 ensures efficient carrier transport, avoiding the problem of "increased charge carrier concentration but decreased mobility." The synergistic optimization of two-dimensional electron gas concentration and mobility in the channel significantly reduces the device's on-resistance. The reduced on-resistance decreases the device's on-state power consumption, alleviates the device's heat generation problem, and thus improves the device's long-term operational reliability and lifespan. At the same time, the synergistic characteristics of "high withstand voltage + low on-resistance" enable the device to meet both high-voltage applications and high-efficiency transmission, satisfying the core requirements of "low loss and high power density" for power electronic devices.

[0029] GaN channel layer 6 retains the high electron mobility advantage of traditional AlGaN / GaN HEMTs (electron mobility can reach 2000 cm⁻¹). 2 / V Compared to schemes using β-Ga2O3 as the channel layer, this avoids the increased conductivity loss caused by the low electron mobility of β-Ga2O3 (only 1 / 5 to 1 / 3 of GaN). Simultaneously, the AlGaN barrier layer 7, as a mature heterojunction barrier solution, is fully compatible with existing GaN device electrode fabrication and passivation processes, requiring no process system reconstruction. The device maintains high carrier transport speed while exhibiting low on-resistance, resulting in excellent switching response characteristics. It boasts strong process adaptability, directly connecting to existing GaN epitaxy and device fabrication production lines. The combination of high switching speed and low loss enables the device to be adapted to high-frequency applications (such as RF power amplifiers and high-frequency switching power supplies), further expanding its application areas. Process compatibility lowers the industrialization threshold, avoiding additional costs such as equipment modification and process development due to the introduction of new materials, and shortening the technology transfer cycle.

[0030] Traditional back-barrier-free solutions suffer from low withstand voltage and high leakage current; single-layer AlGaN back-barrier solutions offer improved withstand voltage but fail to eliminate parasitic leakage current and increase on-resistance; and single-layer β-Ga2O3 back-barrier solutions lack parasitic channels but suffer from poor bandgap matching with the channel layer and limited on-resistance optimization. This application, however, achieves three core characteristics simultaneously—no parasitic channels, high withstand voltage, and low on-resistance—through a "β-Ga2O3 / AlGaN composite back-barrier + complementary material properties" design, overcoming the performance limitations of traditional solutions. The device's overall performance (withstand voltage, on-resistance, switching speed, and reliability) is comprehensively superior to existing solutions, forming a differentiated technological advantage. This provides an industrializable technological path for high-voltage, high-power, and high-frequency GaN-based devices, driving the development of GaN power electronic devices towards higher voltage, higher efficiency, and higher power density, and contributing to the upgrading of power electronic systems in new energy, rail transportation, aerospace, and other fields.

[0031] As one possible implementation, the substrate 1 is made of Si, Al2O3 or SiC.

[0032] It should be noted that Si substrates are low in cost, scalable in size (e.g., 8-inch, 12-inch wafers), have good thermal conductivity, and are highly compatible with semiconductor integrated circuit processes, making them suitable for cost-sensitive large-scale applications such as consumer electronics. Al2O3 (sapphire) substrates have excellent chemical stability and good insulation properties. The lattice mismatch with GaN materials can be effectively mitigated by the AlN nucleation layer 2, making them a classic substrate for GaN epitaxial growth and suitable for medium and high voltage power devices and other applications with high voltage withstand requirements. SiC substrates have wide bandgap characteristics, high thermal conductivity, and high lattice matching with GaN, which can effectively reduce the defect density of the epitaxial layer. At the same time, they have excellent voltage withstand performance and are suitable for power electronic devices in high voltage, high power, and high temperature environments (such as new energy vehicle inverters and high voltage power modules).

[0033] As one possible implementation, the thickness of the β-Ga2O3 layer 4 is 5-50 nm, and the thickness of the AlGaN layer 5 is 10-100 nm.

[0034] It should be noted that if the thickness of the β-Ga2O3 layer 4 is too thin (less than 5 nm), the barrier height will be insufficient, failing to effectively prevent channel electrons from leaking to the buffer layer; if the thickness of the β-Ga2O3 layer 4 is too thick (greater than 50 nm), stress accumulation will occur due to the lattice mismatch between β-Ga2O3 and GaN (approximately 4%), increasing the defect density of the epitaxial layer. If the thickness of the AlGaN layer 5 is too thin (less than 10 nm), it cannot effectively improve the conduction band and reduce carrier overflow to the buffer layer; if the thickness of the AlGaN layer 5 is too thick (greater than 100 nm), the accumulated stress due to the lattice mismatch with GaN will be too large, increasing the defect density of the epitaxial layer.

[0035] As one possible implementation, the resistivity of GaN buffer layer 3 is greater than 1×10⁻⁶. 9 Ω˙cm.

[0036] It should be noted that in traditional solutions, even with the introduction of a single-layer AlGaN back barrier, the intrinsic leakage current of the low-resistivity GaN buffer layer 3 itself still limits the improvement of the device's breakdown voltage. In this application, the core function of the high-resistivity GaN buffer layer 3 is to work with the composite back barrier layer to form a "dual leakage current suppression" system: the high-resistivity GaN buffer layer 3, as the lower support layer of the composite back barrier layer, can directly reduce its own intrinsic leakage current (such as thermally excited leakage current and impurity ionization leakage current) due to its high resistance characteristics. At the same time, the composite back barrier layer blocks the diffusion leakage current of channel electrons to the buffer layer, thus completely cutting off the leakage current path of the buffer layer from two dimensions. By controlling the doping concentration (low doping or no doping) and optimizing the growth temperature and atmosphere during MOCVD epitaxial growth, the GaN buffer layer 3 is made into a high-resistivity state. This preparation method is fully compatible with the subsequent growth process of the composite back barrier layer and does not require additional process steps. At the same time, the lattice structure of the high-resistivity GaN buffer layer 3 is not affected by the lattice matching of β-Ga2O3 and GaN channel layer 6, which can ensure the integrity of the heterostructure interface and avoid the increase of defects caused by resistance adjustment.

[0037] As one possible implementation method, such as Figures 1 to 2 As shown, a p-GaN layer and / or a GaN cap layer are also disposed on the AlGaN barrier layer 7.

[0038] It should be noted that the p-GaN layer is made of p-type doped GaN material (commonly Mg doped), forming an electrical coupling with the underlying AlGaN barrier layer 7 and GaN channel layer 6. Its core function is to adjust the band structure of the gate 9 region to achieve enhancement-mode device characteristics (positive threshold voltage), while simultaneously improving the stability and breakdown voltage of the gate 9 Schottky contact. The GaN cap layer is made of intrinsic or lightly doped GaN material, typically 1-20 nm thick, covering the surface of the AlGaN barrier layer 7 or the p-GaN layer. Its core function is to protect the AlGaN barrier layer 7 from damage by subsequent processes (such as electrode fabrication and passivation layer deposition), reduce surface state density, and optimize the contact characteristics between the electrode and the barrier layer. The two layer structures can be flexibly combined: only a p-GaN layer (suitable for enhancement-mode device requirements), only a GaN cap layer (suitable for the surface protection requirements of depletion-mode devices), or both a p-GaN layer and a GaN cap layer (the p-GaN layer modulates electrical characteristics, and the GaN cap layer provides surface protection), covering the design requirements of different device types.

[0039] The second aspect of the embodiments of this application, such as Figures 1 to 2As shown, a method for fabricating a heterojunction back-barrier GaN HEMT epitaxial structure is provided, which is used to fabricate the aforementioned heterojunction back-barrier GaN HEMT epitaxial structure. The method includes: S100, a core layer 2 and a GaN buffer layer 3 are sequentially grown on the substrate; S200. A composite back barrier layer is grown on the GaN buffer layer 3. The composite back barrier layer includes a β-Ga2O3 layer 4 and an AlGaN layer 5 grown sequentially. S300, GaN channel layer 6 and AlGaN barrier layer 7 are sequentially grown on the composite back barrier layer.

[0040] It should be noted that the preparation method of the heterojunction back barrier GaN HEMT epitaxial structure provided in this embodiment is identical to the specific structure of the heterojunction back barrier GaN HEMT epitaxial structure described above. Those skilled in the art can deduce the preparation method of the heterojunction back barrier GaN HEMT epitaxial structure based on the description of the specific structure of the heterojunction back barrier GaN HEMT epitaxial structure described above, and this application will not repeat the description. Since the preparation method of the heterojunction back barrier GaN HEMT epitaxial structure provided in this embodiment is used to prepare the above-mentioned heterojunction back barrier GaN HEMT epitaxial structure, this preparation method of the heterojunction back barrier GaN HEMT epitaxial structure has the same beneficial effects as the above-mentioned heterojunction back barrier GaN HEMT epitaxial structure, and will not be elaborated further here.

[0041] As one possible implementation, S100, sequentially growing the core layer 2 and the GaN buffer layer 3 on the substrate, includes: S101. A nucleation layer 2 and a GaN buffer layer 3 are sequentially grown on the substrate using MOCVD technology.

[0042] It should be noted that MOCVD is a mature and mainstream process for the epitaxial growth of GaN-based materials. It achieves layer-by-layer growth of thin film materials through a chemical reaction between a metal-organic source (such as trimethylgallium) and a gas source (such as ammonia) under high temperature and low pressure. It possesses core advantages such as controllable growth rate, good film thickness uniformity, precise component doping, and suitability for large-area mass production, perfectly matching the growth requirements of nucleation layer 2 and GaN buffer layer 3. The core function of nucleation layer 2 is to alleviate the lattice mismatch and thermal expansion coefficient difference between the substrate and GaN. The MOCVD process can precisely control the thickness (10-50 nm) and crystal quality of nucleation layer 2 by adjusting the growth temperature (typically 500-800℃), gas flow rate (such as NH3 / H2 ratio), and growth time, providing a flat, low-defect substrate for the subsequent growth of GaN buffer layer 3. GaN buffer layer 3 needs to possess high resistivity characteristics, which can be achieved by controlling the carbon / iron deep-level impurity doping concentration (1.0 × 10⁻⁶). 18 -5.0×1020 cm -3 Optimize the growth temperature (800-1000℃) to enable the GaN buffer layer 3 to form a high-resistivity state, while ensuring its lattice integrity and avoiding leakage channels caused by process defects.

[0043] As one possible implementation, S200, growing a composite back barrier layer on the GaN buffer layer 3 includes: S201. β-Ga2O3 layer 4 and AlGaN layer 5 are sequentially grown on GaN buffer layer 3 using MOCVD or MBE process.

[0044] It should be noted that both MOCVD and MBE processes are mature technologies for epitaxial growth of semiconductor materials and are compatible with β-Ga2O3 and GaN material systems, making them preferred processes for achieving high-quality composite back barrier layers. Among them, the MOCVD process has the advantages of controllable growth rate and suitability for large-area mass production, while the MBE process is characterized by high growth precision and excellent interface quality. The two processes can be flexibly selected according to industrialization needs and performance targets. β-Ga2O3 is a polarization-free ultrawide bandgap material, and its crystal quality directly affects the heterointerface performance with GaN buffer layer 3. The crystal quality of AlGaN layer 5 directly affects the heterointerface performance with GaN channel layer 6. The MOCVD process can precisely control the thickness (e.g., 5-50 nm) and compositional uniformity of the β-Ga2O3 layer by adjusting the flow rate of the reaction source (e.g., trimethylgallium, oxygen), the growth temperature (e.g., 600-900℃), and the pressure. The MBE process, on the other hand, uses molecular beams generated by thermal evaporation or electron beam evaporation to deposit and grow on the substrate surface, which can achieve atomically flat β-Ga2O3 films at lower temperatures (e.g., 500-700℃), reducing interlayer diffusion and defects caused by high temperatures. For AlGaN layer 5, both MOCVD and MBE can achieve high-quality epitaxial growth. MOCVD precisely controls the Al composition (e.g., 0.1-0.3 nm) and layer thickness (e.g., 10-100 nm) by reacting trimethylaluminum, trimethylgallium and ammonia. MBE, on the other hand, precisely controls the Al composition and interface steepness at the atomic scale by adjusting the molecular beam flux ratio of the aluminum source and the gallium source.

[0045] As one possible implementation, S300, sequentially growing a GaN channel layer 6 and an AlGaN barrier layer 7 on the composite back barrier layer includes: S301. A GaN channel layer 6 and an AlGaN barrier layer 7 are sequentially grown on the composite back barrier layer using MOCVD technology.

[0046] It should be noted that MOCVD is a mature and mainstream process for growing GaN-based heterojunction materials. By precisely controlling the reaction conditions of the metal-organic source (such as trimethylgallium, trimethylaluminum) and the gas source (such as ammonia), high-quality and high-uniform growth of GaN and AlGaN films can be achieved, which fully matches the structural requirements of "GaN channel layer 6 + AlGaN barrier layer 7". The GaN channel layer 6 is the core channel for carrier transport and needs to have high electron mobility. The MOCVD process can control the crystal quality of the GaN channel layer 6, reduce the defect density, and ensure carrier transport efficiency by optimizing the growth temperature (900-1100℃) and gas ratio (NH3 / Ga source ratio). The AlGaN barrier layer 7 needs to form a heterojunction with the GaN channel layer 6 and use the polarization effect to induce a high concentration of two-dimensional electron gas (2DEG). The MOCVD process can precisely adjust the Al composition (usually Al composition 0.15-0.3) and layer thickness (15-30nm) to ensure the stability of polarization charge accumulation and 2DEG concentration, and form a functional synergy with the composite back barrier layer.

[0047] A third aspect of this application provides a heterojunction back-barrier GaN HEMT device, including the aforementioned heterojunction back-barrier GaN HEMT epitaxial structure. A source 8, a gate 9, and a drain 10 are disposed on the epitaxial structure. The gate 9 can be a Schottky contact electrode, and the source 8 and drain 10 can be ohmic contact electrodes. Since the structure and beneficial effects of the heterojunction back-barrier GaN HEMT epitaxial structure have been described in detail in the foregoing embodiments, they will not be repeated here.

[0048] Figure 3 The image shows a band structure comparison of the heterojunction back barrier (i.e., the composite back barrier layer) provided in the embodiments of this application with a monolayer AlGaN back barrier, a monolayer β-Ga2O3 back barrier, and a GaN HEMT device without a back barrier. It can be seen that the composite back barrier layer avoids the parasitic channel at the interface between the monolayer AlGaN back barrier and the GaN buffer layer 3, and also avoids the problem of conduction band reduction at the interface between the monolayer β-Ga2O3 back barrier and the GaN channel layer 6.

[0049] Figure 4 This is a current distribution diagram of a heterojunction back barrier GaN HEMT device during breakdown, provided in an embodiment of this application. Figure 5 The diagram shows the current distribution during breakdown of a single-layer AlGaN back-barrier GaN HEMT device provided in this embodiment. It can be seen that the heterojunction back-barrier GaN HEMT device has no buffer layer punch-through current during breakdown.

[0050] Figure 6This diagram compares the breakdown voltages of a heterojunction back-barrier GaN HEMT device and a monolayer AlGaN back-barrier GaNHEMT device provided in the embodiments of this application. It can be seen that the breakdown voltage of the heterojunction back-barrier GaN HEMT device is significantly higher than that of the monolayer AlGaN back-barrier GaN HEMT device.

[0051] The above description is merely an optional embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0052] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.

Claims

1. A heterojunction back-barrier GaN HEMT epitaxial structure, characterized in that, The device includes a substrate layer, a nucleation layer disposed on the substrate layer, a GaN buffer layer disposed on the nucleation layer, a composite back barrier layer disposed on the GaN buffer layer, a GaN channel layer disposed on the composite back barrier layer, and an AlGaN barrier layer disposed on the GaN channel layer; wherein the composite back barrier layer includes a β-Ga2O3 layer disposed on the GaN buffer layer and an AlGaN layer disposed on the β-Ga2O3 layer.

2. The heterojunction back barrier GaN HEMT epitaxial structure according to claim 1, characterized in that, The substrate is made of Si, Al2O3, SiC or GaN.

3. The heterojunction back barrier GaN HEMT epitaxial structure according to claim 1, characterized in that, The thickness of the β-Ga2O3 layer is 5-50 nm, and the thickness of the AlGaN layer is 10-100 nm.

4. The heterojunction back barrier GaN HEMT epitaxial structure according to claim 1, characterized in that, The resistivity of the GaN buffer layer is greater than 1×10⁻⁶. 9 Ω˙cm.

5. The heterojunction back barrier GaN HEMT epitaxial structure according to claim 1, characterized in that, A p-GaN layer and / or a GaN cap layer are also disposed on the AlGaN barrier layer.

6. A method for fabricating a heterojunction back-barrier GaN HEMT epitaxial structure, used to fabricate the heterojunction back-barrier GaN HEMT epitaxial structure as described in any one of claims 1-5, characterized in that, The method includes: A core layer and a GaN buffer layer are sequentially grown on the substrate; A composite back barrier layer is grown on the GaN buffer layer, the composite back barrier layer comprising a β-Ga2O3 layer and an AlGaN layer grown sequentially. A GaN channel layer and an AlGaN barrier layer are sequentially grown on the composite back barrier layer.

7. The method for fabricating a heterojunction back barrier GaN HEMT epitaxial structure according to claim 6, characterized in that, The sequential growth of the core layer and the GaN buffer layer on the substrate includes: A nucleation layer and a GaN buffer layer were sequentially grown on the substrate using MOCVD technology.

8. The method for fabricating a heterojunction back barrier GaN HEMT epitaxial structure according to claim 6, characterized in that, The growth of the composite back barrier layer on the GaN buffer layer includes: A β-Ga2O3 layer and an AlGaN layer are sequentially grown on the GaN buffer layer using MOCVD or MBE processes.

9. The method for fabricating a heterojunction back barrier GaN HEMT epitaxial structure according to claim 6, characterized in that, The sequential growth of a GaN channel layer and an AlGaN barrier layer on the composite back barrier layer includes: A GaN channel layer and an AlGaN barrier layer were sequentially grown on the composite back barrier layer using the MOCVD process.

10. A heterojunction back barrier GaN HEMT device, characterized in that, The heterojunction back barrier GaN HEMT epitaxial structure as described in any one of claims 1-5 is provided with a source, a gate, and a drain on the epitaxial structure.

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