GaN-based hbt device with algan graded layer and tunnel junction and simulation optimization method
By introducing an AlGaN gradient layer and synergistically controlling the tunnel junction in GaN-based HBT devices, a narrow depletion region and smooth band transition are formed, solving the problems of low current gain and high base recombination loss, and achieving device performance with high current gain and low power consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF POSTS & TELECOMM
- Filing Date
- 2026-05-25
- Publication Date
- 2026-07-24
Smart Images
Figure CN122458445A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor device design and simulation technology, specifically involving GaN-based HBT devices and simulation optimization methods based on the synergistic regulation of AlGaN graded layers and tunnel junctions. Background Technology
[0002] Gallium nitride (GaN) materials possess advantages such as a wide bandgap, high critical breakdown field strength, high electron saturation drift velocity, high temperature resistance, and strong radiation resistance, making them valuable for applications in high-power, high-frequency electronic devices and optoelectronic integrated devices. Heterojunction bipolar transistors (HBTs) based on GaN materials exhibit characteristics such as longitudinal carrier transport, strong current driving capability, output current controllable by base current, and ease of monolithic integration with optoelectronic devices such as GaN-based light-emitting diodes (LEDs). Therefore, they show potential applications in high-frequency power amplification, low-power driving, and optoelectronic integrated systems.
[0003] Existing GaN-based HBT devices still face problems such as low current gain, high base recombination loss, and insufficient emitter junction carrier injection efficiency. The main reason is that the Mg acceptor activation energy in p-type GaN is high, and the effective hole concentration is limited at room temperature, resulting in high base resistance and base current loss. While increasing base doping or thinning the base region can reduce base resistance and shorten carrier transport paths to some extent, it may also increase recombination loss and increase the difficulty of epitaxial growth and process control. Traditional AlGaN / GaN HBTs usually improve emitter efficiency by increasing emitter doping concentration, introducing AlGaN emitter regions, or controlling heterojunction energy. However, excessive doping can easily introduce defects and impurity scattering, and abrupt heterojunctions can easily form band spikes, polarization charge accumulation, and local electric field concentration near the emitter junction, making it difficult to simultaneously achieve high current gain, low injection barrier, and high voltage stability. The tunnel junction structure can enhance interband tunneling transport by utilizing the narrow depletion region formed between heavily doped p-type GaN and n-type GaN, thereby improving the carrier injection capability across the junction under low bias voltage. However, the introduction of the tunnel junction alone may still be limited by the polarization effect, incomplete ionization effect and local bandgap of GaN material. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide GaN-based HBT devices and simulation optimization methods that synergistically regulate AlGaN graded layers and tunnel junctions, thereby solving the problems in existing technologies.
[0005] The objective of this invention can be achieved through the following technical solutions: A GaN-based HBT device synergistically controlled by an AlGaN graded layer and a tunnel junction includes, from bottom to top, a secondary collector region, a collector region, a base region, a tunnel junction layer, an AlGaN graded layer, and an emitter region; The tunnel junction layer comprises a heavily doped p-type GaN layer and a heavily doped n-type GaN layer, wherein the heavily doped p-type GaN layer is closer to the base region, and the heavily doped n-type GaN layer is closer to the AlGaN gradient layer; the doping concentration of both the heavily doped p-type GaN layer and the heavily doped n-type GaN layer is 1×10⁻⁶. 19 cm -3 Up to 5×10 20 cm -3 ; The Al composition in the AlGaN graded layer decreases from the emitter region to the base region.
[0006] Furthermore, an emitter is disposed above the emitter region; base electrodes are disposed on both sides of the emitter region and are in electrical contact with the heavily doped n-type GaN layer in the tunnel junction layer; and a collector electrode is disposed on the side of the collector region or the secondary collector region.
[0007] Furthermore, the emitter region is an n-type AlGaN layer with a thickness of 50~300 nm and a doping concentration of 5×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 .
[0008] Furthermore, the base region is a p-type GaN layer with a thickness of 30~150 nm and a doping concentration of 5×10⁻⁶. 17 cm -3 ~8×10 18 cm -3 .
[0009] Furthermore, the secondary collector region is an n+ type GaN layer with a thickness of 0.5~2 μm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 The current collector region is an n-type GaN layer with a thickness of 200~1000 nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 18 cm -3 .
[0010] Furthermore, the AlGaN gradient layer is Al x Ga 1-xThe N-gradient component layer, where x represents the mole fraction of Al, the maximum value of the mole fraction of Al x does not exceed 30%, and the mole fraction of Al x decreases to 0 near the tunnel junction.
[0011] The simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layers and tunnel junctions, as described above, includes the following steps: S1. Establish a structural model of a GaN-based HBT device in the simulation platform, set the material type, thickness, and doping parameters of each region in the structural model, and set the collector, base, and emitter. S2, Introduce a semiconductor physical model that includes a polarization effect model and an interband tunneling model into the structural model; S3. Apply a bias voltage to the structural model to perform voltage scan simulation and extract the corresponding device electrical characteristic parameters, band distribution and electric field distribution. S4, change at least one parameter among the Al composition distribution of the AlGaN gradient layer, the thickness or doping concentration of the heavily doped p-type GaN layer and the heavily doped n-type GaN layer, repeat S3 to obtain multiple sets of simulation results after changing the parameters, and select the parameters that meet the preset conditions as the optimized device structure parameters.
[0012] Furthermore, the semiconductor physical model also includes: an incomplete ionization model for simulating the ionization characteristics of acceptor impurities in the base region, and a mobility degradation model, an SRH recombination model, and an Auger recombination model for describing carrier transport characteristics.
[0013] Furthermore, the process of applying a bias voltage to the structural model for voltage scanning simulation includes: fixing the voltage between the collector and the emitter, and scanning the voltage between the base and the emitter; the electrical characteristic parameters of the device include: base current, collector current, and current gain.
[0014] Furthermore, the preset condition is that the collector current of the structural model is greater than a preset current threshold, and the peak value of the electric field inside the structural model does not exceed a preset breakdown electric field threshold.
[0015] The beneficial effects of this invention are: 1. This invention introduces a tunnel junction composed of p++-GaN layers and n++-GaN layers near the emitter junction of a GaN-based HBT, thereby forming a narrow depletion region near the emitter junction and generating interband tunneling transport, which helps to reduce the electron injection barrier and improve the electron injection efficiency under low forward bias.
[0016] 2. This invention improves carrier transport capability by setting an AlGaN composition gradient layer between the n-type AlGaN emitter region and the GaN tunnel junction region, so that the Al composition gradually decreases along the direction from the emitter region to the base region, smoothing the conduction band transition, reducing the potential barrier discontinuity caused by the abrupt heterojunction.
[0017] 3. This invention combines tunnel junction-assisted injection with gradual control of AlGaN emitter composition. While enhancing low-bias tunneling transport, it optimizes the emitter-side band structure, which can alleviate the trade-off between emitter efficiency and base recombination loss in GaN-based HBTs, allowing a larger collector current to be controlled with a smaller base current.
[0018] 4. This invention optimizes the device structure parameters through TCAD numerical simulation, enabling the prediction of the effects of AlGaN gradient layer, tunnel junction layer, emitter region and base region parameters on device current gain, collector current, band distribution, electric field distribution and frequency response before device fabrication, thereby reducing the number of experimental trials and errors and lowering R&D costs.
[0019] 5. The simulation results of this invention show that, under the same simulation conditions, the peak current gain and collector current of the device are significantly improved after the introduction of the tunnel junction and the AlGaN gradient layer. At the same time, the device exhibits good low base current control capability and low emitter doping sensitivity, providing an effective technical solution for the design of high-gain, low-power GaN-based bipolar devices and their optoelectronic integrated devices. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 A schematic diagram of the GaN-based HBT device structure and bandgap modulation provided in an embodiment of the present invention; Figure 2 A schematic diagram of the carrier transport and current gain characteristics of a GaN-based HBT device provided in an embodiment of the present invention; Figure 3 A comparison diagram of the electrical characteristics of different structural schemes of GaN-based HBT devices provided in the embodiments of the present invention; Figure 4 Simulation diagram of electrical characteristics of GaN-based HBT device under changes in key structural parameters provided in embodiments of the present invention; Figure 5Simulation diagram of electric field distribution and breakdown characteristics of GaN-based HBT device provided in the embodiments of the present invention. Detailed Implementation
[0022] 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, and 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.
[0023] A GaN-based HBT device synergistically modulated by an AlGaN graded layer and a tunnel junction comprises, from bottom to top: a secondary collector region, a collector region, a base region, a tunnel junction layer, an AlGaN graded layer, and an emitter region. The GaN-based HBT device is a vertical npn-type AlGaN / GaN HBT, and the secondary collector region is an n+ type GaN layer with a thickness of 0.5-2 μm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 The current collector region is an n-type GaN layer with a thickness of 200~1000 nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The base region is a p-type GaN layer with a thickness of 30~150 nm and a doping concentration of 5×10⁻⁶. 17 cm -3 ~8×10 18 cm -3 The emitter region is an n-type AlGaN layer with a thickness of 50~300 nm and a doping concentration of 5×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 .
[0024] The tunnel junction layer comprises a p++-GaN layer and an n++-GaN layer. The p++-GaN layer is disposed near the p-type GaN base region, and the n++-GaN layer is disposed near the n-type AlGaN emitter region. The doping concentration of both the p++-GaN layer and the n++-GaN layer is 1×10⁻⁶. 19 cm -3 ~5×10 20 cm -3 The thickness of each is 5~50 nm.
[0025] In a preferred embodiment, the p++-GaN layer has a thickness of 20 nm and a doping concentration of 1×10⁻⁶. 20 cm -3 The n++-GaN layer has a thickness of 10 nm and a doping concentration of 1×10⁻⁶. 20 cm -3 The n-type AlGaN emitter region has a thickness of 150 nm and a doping concentration of 1 × 10⁻⁶. 19 cm -3 The p-type GaN base region has a thickness of 70 nm and a doping concentration of 3 × 10⁻⁶. 18 cm -3 The thickness of the n-type GaN collector region is 500 nm; the thickness of the n+ type GaN secondary collector region is 1 μm.
[0026] Preferably, the Al composition in the AlGaN graded layer gradually decreases from the side closer to the emitter region to the side closer to the tunnel junction layer, with the Al composition varying from 0% to 30%. More preferably, the Al composition in the AlGaN graded layer gradually decreases from 15% to 0%, which is used to smooth the band transition between the n-type AlGaN emitter region and the GaN tunnel junction region.
[0027] A simulation optimization method for GaN-based HBT devices synergistically modulated by AlGaN graded layers and tunnel junctions, the steps of which include: (1) Establishment of GaN-based heterojunction bipolar transistor structure model A two-dimensional or three-dimensional simulation model of a GaN-based heterojunction bipolar transistor is established in the TCAD simulation platform. The simulation model adopts a vertical npn type AlGaN / GaN HBT structure, which includes a secondary collector region, a collector region, a base region, a tunnel junction layer, an AlGaN gradient layer, and an emitter region arranged sequentially from bottom to top. The material type, thickness, doping type, doping concentration, and the positions of the emitter, base, and collector are set for each region.
[0028] (2) Setting of tunnel structure A tunnel junction layer is formed between the base region and the emitter region. This tunnel junction layer comprises a heavily doped p-type GaN layer near the base region and a heavily doped n-type GaN layer near the emitter region. The heavily doped p-type and n-type GaN layers create a narrow depletion region, enabling interband tunneling transport of charge carriers near the emitter junction. This reduces the potential barrier that electrons must overcome when injected from the emitter region to the base region, thereby improving the cross-junction transport capability of charge carriers under low bias voltage.
[0029] (3) Setting of AlGaN gradient layer An AlGaN graded-layer is disposed between the emitter region and the tunnel junction layer. The Al composition in the AlGaN graded-layer decreases continuously or stepwise along the direction from the emitter region to the base region. By controlling the conduction band and valence band distribution between the emitter region and the tunnel junction region through the gradual change in Al composition, the band discontinuity caused by abrupt heterojunction is reduced, making it easier for electrons to be transported from the emitter region to the base region and further collected by the collector region.
[0030] (4) Setting up the physical model of semiconductor devices The TCAD simulation model incorporates an incomplete ionization model, a concentration-dependent mobility model, an electric field-dependent mobility model, an SRH recombination model, an Auger recombination model, a polarization model, and an interband tunneling model. Specifically, the incomplete ionization model describes the effect of insufficient ionization of the main impurity in p-type GaN; the mobility model describes the influence of doping concentration and electric field on carrier transport; the recombination model describes the carrier recombination process in the base region and near the interface; the polarization model describes the polarization charge effect in GaN-based heterostructures; and the interband tunneling model describes the tunneling transport behavior between heavily doped p-type GaN layers and heavily doped n-type GaN layers.
[0031] (5) Simulation analysis of device electrical characteristics A voltage sweep simulation was performed on the GaN-based heterojunction bipolar transistor (HBT) by applying base-emitter and collector-emitter voltages to obtain the base current, collector current, current gain, output characteristic curves, band structure, current density distribution, electric field distribution, and frequency response. By comparing the simulation results of an HBT with a tunnel junction structure with those of a conventional HBT without a tunnel junction structure, the effects of tunnel junction-assisted injection and AlGaN composition gradient on the current gain and collector current were analyzed.
[0032] (6) Optimization of device structure parameters The Al composition distribution, gradient layer thickness, tunnel junction thickness, tunnel junction doping concentration, emitter doping concentration, base thickness, and base doping concentration of the AlGaN gradient layer were varied. Based on the simulation results of current gain, collector current, base current, emitter junction barrier height, tunneling current density, base recombination intensity, electric field peak value, and frequency response, the optimized device structure parameters were determined.
[0033] The voltage scan simulation in step (5) includes fixing the collector-emitter voltage and scanning the base-emitter voltage to obtain the Gummel curve, base current, collector current and current gain; and scanning the collector-emitter voltage under different base current conditions to obtain the output characteristic curve and device current regulation capability.
[0034] The band distribution in step (5) includes the conduction band, valence band, and quasi-Fermi level distributions in the emitter region, AlGaN graded layer, tunnel junction layer, base region, collector region, and sub-collector region; the current density distribution includes the electron current density distribution and hole current density distribution; and the frequency response includes the characteristics of current gain changing with frequency under different base bias conditions.
[0035] The optimized device structure parameters described in step (6) are determined by the following conditions: Under the same simulation conditions, the HBT with tunnel junction and AlGaN gradient layer has higher collector current and current gain than the conventional HBT without tunnel junction; it has a larger collector output current under the same base current; the conduction band barrier near the emitter junction is reduced; the base recombination loss is reduced; no abnormal electric field concentration occurs in the tunnel junction region; and the device is less sensitive to changes in emitter doping concentration.
[0036] The technical solution of the present invention will be specifically described below through the following embodiments: Example 1 In this embodiment, a simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layer and tunnel junction is proposed, including the following steps: (1) Establish a simulation structure model of GaN-based heterojunction bipolar transistor.
[0037] A two-dimensional GaN-based heterojunction bipolar transistor model was established using the ATLAS device simulation module in Silvaco TCAD software. As shown in Figure 1(a), the device is a vertical npn-type AlGaN / GaN HBT structure, consisting of an n+ type GaN secondary collector region, an n-type GaN collector region, a p-type GaN base region, a p++ type GaN layer, an n++ type GaN layer, and an n-type AlGaN emitter region, from bottom to top. The n+ type GaN secondary collector region has a thickness of 1000 nm and a doping concentration of 3 × 10⁻⁶. 18 cm -3 The n-type GaN collector region has a thickness of 500 nm and a doping concentration of 1×10⁻⁶. 17 cm -3 The p-type GaN base region has a thickness of 70 nm and a doping concentration of 3 × 10⁻⁶. 18cm -3 The p++ type GaN layer and the n++ type GaN layer together form a tunnel junction structure near the emitter junction, with a doping concentration of 1×10⁻⁶ for both. 20 cm -3 The n-type AlGaN emitter region has a thickness of 150 nm and a doping concentration of 1 × 10⁻⁶. 19 cm -3 .
[0038] In this embodiment, the emitter (E) is positioned above the n-type AlGaN emitter region, and the base (B) is positioned on both sides of the emitter region, forming an electrical contact with the heavily doped n-type GaN layer in the tunnel junction. The collector (C) is positioned on the side of the collector region or the secondary collector region. Thus, the base is not directly positioned on both sides of the p-type GaN base region, but rather through contact with the heavily doped n-type region above the tunnel junction, thereby controlling carrier transport near the emitter junction and the base region injection process. The collector (C) is positioned on the side of the collector region or the secondary collector region, thus forming the HBT simulation structure under common-emitter operation. To improve the computational accuracy near the tunnel junction and emitter junction, local mesh refinement is performed near the p++ type GaN layer, the n++ type GaN layer, the AlGaN gradient layer, and the base region.
[0039] (2) Set up an AlGaN gradient layer and tunnel junction structure.
[0040] like Figure 1 As shown in (b), an AlGaN graded-component layer is disposed between the n-type AlGaN emitter region and the GaN tunnel junction region. The AlGaN graded-component layer is disposed between the n-type AlGaN emitter region and the n++ type GaN layer in the tunnel junction layer, and the AlGaN graded-component layer is Al... x Ga 1-xThe AlGaN gradient layer has an N-type emitter region, where x represents the mole fraction of Al. Along the thickness direction of the AlGaN gradient layer, i.e., from the side near the n-type AlGaN emitter region to the side near the n++ type GaN layer in the tunnel junction, the Al mole fraction x decreases linearly. In a specific embodiment, the thickness of the AlGaN gradient layer is 20 nm, the Al mole fraction x near the n-type AlGaN emitter region is 0.15, and the Al mole fraction x near the n++ type GaN layer is 0, meaning the Al mole fraction linearly decreases from 15% to 0%. This gradient composition design makes the conduction band transition between the n-type AlGaN emitter region and the GaN tunnel junction region smoother, reducing band spikes and electron injection barriers caused by abrupt heterojunctions.
[0041] In this embodiment, the tunnel junction is composed of a heavily doped p++ type GaN layer and a heavily doped n++ type GaN layer, and is disposed near the EB junction between the emitter and base regions. Since both the p++ type GaN layer and the n++ type GaN layer are highly doped, their depletion regions are narrower, which is beneficial for forming interband tunneling channels under forward bias conditions, thereby enhancing the electron injection capability from the emitter region to the base region. In an optional embodiment, a junction can also be disposed inside the tunnel junction. The auxiliary tunneling layer, the The auxiliary tunneling layer is located between the heavily doped p-type GaN layer and the heavily doped n-type GaN layer, where x represents the mole fraction of In. In a specific embodiment, the... The auxiliary tunneling layer has an In mole fraction (x) of 0.3 and a thickness of 5 nm. This is achieved by inserting this [material] between the p++ GaN layer and the n++ GaN layer. The N-assisted tunneling layer can utilize the narrow bandgap and polarization effect of InGaN material to adjust the band bending and local electric field distribution in the tunnel junction region, enhance the overlap of electron and hole wave functions, and thus improve the interband tunneling probability and tunneling injection efficiency.
[0042] (3) Set up the physical model of the semiconductor device.
[0043] After completing the device structure and doping parameter settings, physical models related to GaN-based materials and tunnel junction transport were introduced into the TCAD simulation, including the incomplete ionization model, concentration-dependent mobility model, electric field-dependent mobility model, SRH recombination model, Auger recombination model, polarization model, and interband tunneling model. The incomplete ionization model is used to describe the problem that Mg acceptors in p-type GaN cannot be completely ionized at room temperature and under different temperature conditions; the concentration-dependent mobility model and the electric field-dependent mobility model are used to describe the effects of doping concentration and high electric field on carrier mobility; the SRH recombination model and the Auger recombination model are used to describe carrier recombination losses in the base region and near the junction region; the polarization model is used to describe the spontaneous polarization and piezoelectric polarization effects in AlGaN / GaN heterojunctions; and the interband tunneling model is used to describe the tunneling transport process between p++ type GaN layers and n++ type GaN layers.
[0044] Specifically, in the incomplete ionization model, the Mg acceptor activation energy in the p-type GaN base region and p++ type GaN tunnel junction is set to 0.17 eV to describe the phenomenon that the effective hole concentration is lower than the nominal doping concentration because the Mg acceptor cannot be completely ionized at room temperature; the Si donor activation energy in the n-type GaN, n++ type GaN and n-type AlGaN regions is set to 0.017 eV.
[0045] In the polarization model, spontaneous polarization and piezoelectric polarization effects in GaN-based heterostructures are considered, and a polarization charge scaling factor is introduced to correct the effective polarization charge intensity caused by dislocations, interface states, stress relaxation, and surface compensation effects in actual epitaxial materials. In this embodiment, the polarization charge scaling factor is set to 0.5–1.0, preferably 0.8.
[0046] In the interband tunneling model, a Kane-type interband tunneling model or an equivalent local interband tunneling model is used to describe the tunneling transport behavior between heavily doped p++-GaN layers and n++-GaN layers. The effective tunneling mass is set to 0.20. ~0.30 The preferred setting is 0.25. ,in Let B be the rest mass of the free electron. The exponential factor B in the Kane tunneling model is set to 1.5 × ~3.0× V / cm, preferably set to 2.0× V / cm; the pre-factor A in the Kane tunneling model is set to 1.0× ~1.0× · The preferred setting is 5.0× · By setting the above parameters, the effects of incomplete ionization of Mg acceptors, polarization charge at the AlGaN / Ga heterojunction interface, and interband tunneling transport in the p++ / n++ GaN tunnel junction region on the device current density distribution, Gummel characteristics, and current gain can be simultaneously reflected in the simulation. (4) Conduct simulation analysis of band distribution and tunneling mechanism.
[0047] A small emitter junction bias voltage was applied to the GaN-based heterojunction bipolar transistor, and the conduction band and valence band distributions inside the device were extracted. As shown in Figure 1(c), corresponding band changes can be observed in the emitter region, tunnel junction region, base region, collector region, and sub-collector region. Figure 1(d) is a magnified band structure of the tunnel junction region. It can be seen that due to the high doping effect of the n++ type GaN layer and p++ type GaN layer, the depletion region width of the tunnel junction region is significantly compressed, and the local band is bent, allowing electrons on the emitter side to enter the region near the base region through a tunneling-assisted mechanism.
[0048] In this structure, the AlGaN gradient layer smooths the band transition from the emitter region to the tunnel junction region, while the tunnel junction lowers the potential barrier that electrons must overcome to cross the emitter junction. Together, they enable the device to achieve strong electron injection capability at a relatively low forward bias.
[0049] (5) Perform current density and Gummel characteristic simulation.
[0050] Under base-emitter bias conditions, the electron current density and hole current density distribution inside the device were extracted. As shown in Figure 2(a), electrons are mainly injected from the emitter region, transported through the base region, and then enter the collector region and the secondary collector region, indicating that this structure can form an effective longitudinal electron transport channel. Figure 2 As shown in (b), the hole current is mainly concentrated in the base region and near the emitter junction, indicating that hole transport and recombination in the base region mainly occur in the region near the emitter junction.
[0051] Further scanning of the base-emitter voltage under a fixed collector junction bias yielded the Gummel characteristic curve shown in Figure 2(c). As the base-emitter voltage increases, both the collector current and base current gradually increase, but the collector current shows a more significant increase. When the base-emitter voltage increases to a certain range, the device current gain rises rapidly, reaching a peak around 3.2 V. This result indicates that tunnel junction-assisted injection and AlGaN gradient bandgap modulation can effectively improve electron injection efficiency, enabling the device to obtain a larger collector current with a smaller base current.
[0052] Example 2 In this embodiment, a comparative simulation method is proposed to verify the modulation effect of tunnel junctions and AlGaN graded layers, the steps of which include: (1) Establish a comparative model of GaN-based HBT with tunnel junction structure and GaN-based HBT without tunnel junction structure.
[0053] Under the same emitter, base, collector, and secondary collector parameters, a TJ HBT structure with a p++ / n++ GaN tunnel junction and a conventional HBT structure without a tunnel junction were established. The same base-emitter voltage and collector-emitter voltage scanning conditions were applied to both models, and the collector current and base current were extracted.
[0054] As shown in Figure 3(a), under the same base-emitter voltage conditions, the HBT with the tunnel junction structure exhibits a higher collector current compared to the HBT without the tunnel junction structure. This result indicates that after introducing a heavily doped tunnel junction near the EB junction, the carrier transport capability across the junction near the emitter junction is enhanced, and electrons can be injected more effectively from the emitter region into the base region and collected by the collector region.
[0055] (2) Compare the collector current-base current characteristics of structures with and without tunnel junction structures.
[0056] As shown in Figure 3(b), under the same base current conditions, the HBT with a tunnel junction structure outputs a larger collector current. This is because the tunnel junction provides an additional tunneling-assisted injection channel, lowers the injection barrier near the emitter junction, improves electron injection efficiency, and reduces recombination losses in the base region, thereby improving the device's current amplification capability.
[0057] (3) Compare the current characteristics of tunnel junction HBTs with AlGaN graded layers and without AlGaN graded layers.
[0058] Based on the tunnel junction structure, TJ HBTs with and without AlGaN graded layers were constructed. As shown in Figure 3(c), under the same base current conditions, the TJ HBT with the AlGaN graded layer achieved a higher collector current. This result indicates that the AlGaN graded layer can improve the band continuity between the emitter region and the tunnel junction region, reduce the suppression effect of local barrier discontinuities on carrier transport, and thus further improve the device output current.
[0059] Example 3 In this embodiment, a parameter scanning simulation method for optimizing the doping concentration of the tunnel junction and the base region is proposed, the steps of which include: (1) Change the doping concentration of the tunnel junction and extract the current characteristics of the device.
[0060] While keeping the structural parameters of the emitter, base, collector, and secondary collector regions unchanged, the doping concentrations of the p++ type GaN layer and the n++ type GaN layer were set to different values, and collector current-base current simulations were performed respectively. As shown in Figure 4(a), the collector current of the device generally increases with the increase of the tunnel junction doping concentration.
[0061] The reason is that a higher doping concentration in the tunnel junction can increase the carrier concentration on both sides of the tunnel junction and further reduce the width of the tunnel junction depletion region, thereby enhancing the overlap of electron and hole wave functions and thus increasing the interband tunneling probability and tunneling current density. Therefore, increasing the doping concentration of p++ / n++ GaN tunnel junctions within a certain range is beneficial to enhancing the tunneling-assisted injection capability near the emitter junction.
[0062] (2) Change the base region doping concentration and extract the collector current-base current characteristics.
[0063] While keeping other structural parameters constant, the doping concentration of the p-type GaN base region was varied, and current characteristics were simulated under a collector-emitter voltage of 8 V. As shown in Figure 4(b), the base region doping concentration has a significant impact on the device's collector current. Changes in the base region doping concentration simultaneously affect the base region resistance, carrier recombination loss, and base region transport capability.
[0064] When the base doping concentration is low, the base resistance is high, which may limit the base modulation capability. When the base doping concentration is too high, base recombination is enhanced, causing more electrons to recombine in the base region, resulting in a decrease in the number of electrons collected by the collector region. Therefore, the base doping concentration needs to be optimized by a trade-off between reducing the base resistance and suppressing recombination losses.
[0065] (3) Change the base region doping concentration and extract the collector current-base emitter voltage characteristics.
[0066] As shown in Figure 4(c), the collector current of the device maintains a consistent trend with the base-emitter voltage under different base doping concentrations, but the magnitude and growth rate of the current after turn-on differ. This result indicates that the base doping concentration not only affects the output current of the device but also the carrier transport and recombination process after emitter junction injection. This parameter scanning method can be used to screen out a range of base doping concentrations that combine low base resistance, low recombination loss, and high current gain.
[0067] Example 4 This embodiment introduces a simulation method for evaluating the electric field distribution and breakdown characteristics of GaN-based heterojunction bipolar transistors, the steps of which include: (1) Establish a simulation model of electric field distribution under high voltage bias conditions.
[0068] After completing the device structure and physical model setup, a gradually increasing collector voltage was applied to the collector while keeping the emitter and base in their respective reference bias states. The two-dimensional electric field distribution inside the device and the electric field intensity distribution along the longitudinal direction were extracted. As shown in Figure 5(a) and Figure 5(b), the electric field of the device under different bias conditions is mainly distributed in the collector region and near the junction region, and no abnormally strong electric field concentration is observed in the tunnel junction region.
[0069] Because GaN material has a high critical breakdown field strength, and the tunnel junction region in this invention employs a heavily doped p++ / n++ structure with a narrow depletion region, it can enhance tunneling transport while avoiding the formation of a large-scale high electric field accumulation. Furthermore, the AlGaN graded layer smooths the energy band and electric field distribution near the emitter junction, which helps reduce local electric field spikes.
[0070] (2) Simulate the collector current-collector voltage breakdown characteristics.
[0071] In the breakdown characteristic simulation, the collector voltage was gradually increased, and the curve of collector current changing with collector voltage was extracted. As shown in Figure 5(c), in the lower collector voltage range, the collector current remains at a low level; when the collector voltage rises to about 187 V, the collector current increases sharply, indicating that the device has entered the breakdown state.
[0072] The results demonstrate that the GaN-based heterojunction bipolar transistor synergistically controlled by the AlGaN graded layer and tunnel junction in this embodiment of the invention maintains good high-voltage stability while preserving high current gain. This high-voltage stability primarily stems from the high critical breakdown field strength of the GaN material itself, the collector region's ability to withstand reverse bias, and the modulating effect of the tunnel junction and AlGaN graded layer on the local electric field distribution.
[0073] This embodiment establishes a TCAD simulation model of a GaN-based TJ HBT and, combined with band distribution, current density distribution, Gummel curves, structural parameter scanning, and breakdown characteristic analysis, verifies the synergistic control effect of the AlGaN graded layer and tunnel junction. Simulation results show that the structure can improve carrier injection conditions near the emitter junction, increase collector current and current gain, and maintain good high-voltage stability.
[0074] Example 5 This embodiment provides the specific fabrication process of the GaN-based HBT device designed in Example 1.
[0075] This method forms a longitudinal npn-type GaN-based HBT epitaxial structure through epitaxial growth, and combines mesa etching, electrode fabrication and dielectric passivation processes to obtain a GaN-based HBT device with an AlGaN gradient layer and a tunnel junction.
[0076] Epitaxial structures can be prepared using plasma-assisted molecular beam epitaxy (PME) or metal-organic chemical vapor deposition (MOCVD). Taking PME as an example, the epitaxial growth equipment is equipped with Ga, Al, In, Si, and Mg source furnaces and a radio frequency nitrogen plasma source. Ga, Al, and In are used as Group III element sources, active nitrogen as a Group V element source, Si as an n-type dopant source, and Mg as a p-type dopant source. During epitaxial growth, the nitrogen plasma power is set to 250–350 W, preferably 300 W; the growth chamber pressure is set to 5 × 10⁻⁶ W. -6 ~5×10 -5 Torr, preferably about 1×10 - 5 Torr; the substrate temperature is set to 700–800 °C, preferably 750 °C; the epitaxial growth rate is set to 2–6 nm / min, preferably about 4 nm / min.
[0077] The substrate used for epitaxial growth is a c-plane conductive GaN substrate. Before entering the epitaxial cavity, the substrate is sequentially cleaned with acetone, isopropanol and deionized water, with each cleaning step lasting 3 to 10 minutes. After cleaning, nitrogen gas is used to dry the substrate to remove surface organic contaminants and particulate residues.
[0078] An n+ type GaN secondary collector region, an n-type GaN collector region, a p-type GaN base region, a p++ type GaN layer, an InGaN auxiliary tunneling layer, an n++ type GaN layer, an AlGaN gradient layer, and an n-type AlGaN emitter region are sequentially formed on the conductive GaN substrate. The n+ type GaN secondary collector region has a thickness of 1000 nm and a Si doping concentration of 3 × 10⁻⁶. 18 cm -3 The n-type GaN collector region has a thickness of 500 nm and a Si doping concentration of 1 × 10⁻⁶. 17 cm -3 The p-type GaN base region has a thickness of 70 nm and a Mg doping concentration of 3 × 10⁻⁶. 18 cm -3The p++ type GaN layer has a thickness of 20 nm and a Mg doping concentration of 1×10⁻⁶. 20 cm -3 The InGaN-assisted tunneling layer is In 0.3 Ga 0.7 The N-layer has a thickness of 5 nm; the n++ type GaN layer has a thickness of 10 nm and a Si doping concentration of 1×10⁻⁶. 20 cm -3 .
[0079] The p++ type GaN layer, In 0.3 Ga 0.7 The N-type auxiliary tunneling layer and the n++ type GaN layer together constitute the tunnel junction. The In... 0.3 Ga 0.7 The N-assisted tunneling layer is located between the p++ type GaN layer and the n++ type GaN layer. It is used to adjust the band bending and local electric field distribution in the tunnel junction region by utilizing the narrow bandgap and polarization effect of InGaN material, thereby increasing the interband tunneling probability.
[0080] An AlGaN gradient layer is formed on top of the n++ type GaN layer. The AlGaN gradient layer is Al... x Ga 1-x N layers, where x represents the mole fraction of Al. The AlGaN gradient layer has a thickness of 20 nm and a Si doping concentration of 1 × 10⁻⁶. 19 cm -3 The Al mole fraction x decreases linearly along the thickness direction from the emitter side to the tunnel junction side, with x=0.15 near the emitter side and x=0 near the n++ type GaN layer. When the thickness direction coordinate t satisfies 0≤t≤20 nm, the Al mole fraction satisfies x(t)=0.15×(1−t / 20). This linearly graded layer is used to smooth the band transition between the n-type AlGaN emitter region and the GaN tunnel junction region, reducing the band spikes and electron injection barriers caused by abrupt heterojunctions.
[0081] An n-type AlGaN emitter region is formed above the AlGaN graded layer. The n-type AlGaN emitter region has a thickness of 150 nm and a Si doping concentration of 1 × 10⁻⁶. 19 cm -3 The Al mole fraction is 0.15. This yields a GaN-based TJ-HBT epitaxial structure comprising a secondary collector region, a collector region, a base region, a tunnel junction layer, an AlGaN graded layer, and an emitter region.
[0082] After the epitaxial structure is completed, a SiO2 layer is deposited on the surface of the epitaxial wafer as a hard mask layer. The SiO2 layer can be formed by plasma-enhanced chemical vapor deposition, with a thickness of 200–300 nm, preferably 250 nm. The active region pattern is defined by photolithography. The SiO2 layer in the exposed areas is removed by CF4 / O2 reactive ion etching, and the residual SiO2 can be removed by wet etching with a buffered oxide etchant.
[0083] The device mesa structure is formed using a BCl3 / Cl2-based inductively coupled plasma etching process. During etching, unetched SiO2 is used as a hard mask, and the etching depth penetrates at least through the n-type AlGaN emitter region, AlGaN gradient layer, n++ type GaN layer, InGaN auxiliary tunneling layer, p++ type GaN layer, and p-type GaN base region, stopping above the n-type GaN collector region or n+ type GaN secondary collector region to form the device active mesa and collector contact area.
[0084] The separation region between the emitter and base is defined by a second photolithography process. The regions located on both sides of the emitter region are locally etched using a low-power BCl3 / Cl2-based ICP-RIE process to expose the n++ type GaN layer in the tunnel junction and form the base contact window. The low-power etching conditions can be set to RIE power of 3–10 W and ICP power of 30–60 W, preferably approximately 5 W for RIE power and approximately 40 W for ICP power, to reduce damage caused by plasma etching to the emitter junction and the region near the tunnel junction. After this local etching, the base contact region is located on both sides of the emitter region and forms an electrical contact with the n++ type GaN layer in the tunnel junction.
[0085] The emitter, base, and collector metal patterns are defined using photolithography. The emitter is positioned above the n-type AlGaN emitter region, the base is positioned on both sides of the emitter region and contacts the n++ type GaN layer, and the collector is positioned in the exposed collector region or sub-collector region. The metal electrodes can be deposited using electron beam evaporation, thermal evaporation, or magnetron sputtering, and the electrode metal can be an Al / Ni / Au or Ti / Al / Ni / Au multilayer metal. In one specific embodiment, the emitter, base, and collector all use an Al / Ni / Au metal multilayer as the ohmic contact metal, and after metal deposition, an independent electrode structure is formed through a lift-off process.
[0086] Device surface passivation is achieved using an Al2O3 dielectric layer. This Al2O3 passivation layer can be formed using atomic layer deposition (ALD) and has a thickness of 50–150 nm, preferably 100 nm. This passivation layer covers the device sidewalls and exposed mesa surfaces, reducing leakage and recombination losses caused by etching sidewall surface states, and also serves as an insulating layer between subsequent pads and the semiconductor surface.
[0087] Contact holes are formed using photolithography and wet or dry etching processes, exposing the emitter, base, and collector metal regions from the Al2O3 passivation layer. The pad metal can be a Ni, Au, or Ni / Au metal stack, deposited via magnetron sputtering, electron beam evaporation, or thermal evaporation. After pad metal deposition and stripping, emitter pads, base pads, and collector pads are formed, resulting in a GaN-based HBT device with synergistic control of the AlGaN graded layer and tunnel junction.
[0088] Using the above fabrication method, the p-type GaN base region, p++ / InGaN / n++ tunnel junction layer, AlGaN linear gradient layer, and n-type AlGaN emitter region can be continuously formed in the same epitaxial structure. The base achieves electrical contact through locally etched exposed n++ type GaN layer, thus avoiding the process difficulties of directly fabricating low-resistance p-type ohmic contacts on the p-type GaN base region. The AlGaN gradient layer and tunnel junction layer together improve the band distribution and carrier transport conditions near the emitter junction, which is beneficial to improving electron injection efficiency and device current gain.
[0089] Specifically, in this embodiment, the specific fabrication method of the device includes the following steps: This embodiment provides a specific fabrication process for a GaN-based HBT device with synergistic control of an AlGaN graded layer and a tunnel junction. The device uses a c-plane conductive GaN substrate, and the epitaxial structure, from bottom to top, includes an n+ type GaN secondary collector region, an n-type GaN collector region, a p-type GaN base region, a p++ type GaN layer, an InGaN auxiliary tunneling layer, an n++ type GaN layer, an AlGaN graded layer, and an n-type AlGaN emitter region.
[0090] In this embodiment, the epitaxial growth equipment used is a VEECO GEN930 plasma-assisted molecular beam epitaxy system. This equipment is equipped with a radio frequency N2 plasma source and Ga, Al, In, Si, and Mg source furnaces. Ga, Al, and In are used as Group III element sources, the radio frequency N2 plasma is used as the nitrogen source, Si is used as the n-type doping source, and Mg is used as the p-type doping source. During the epitaxial growth process, the N2 plasma power is set to 300 W, and the growth chamber pressure is set to 1 × 10⁻⁶ W. -5 Torr, substrate temperature set to 750 ℃, epitaxial growth rate set to 4 nm / min.
[0091] The c-plane conductive GaN substrate was ultrasonically cleaned sequentially with acetone, isopropanol, and deionized water before epitaxial growth. The acetone cleaning time was 5 min, the isopropanol cleaning time was 5 min, and the deionized water rinsing time was 5 min. After cleaning, the substrate was dried with high-purity N2 and placed in the sample loading chamber of the molecular beam epitaxy equipment for vacuum pretreatment.
[0092] An n+ type GaN secondary collector region with a thickness of 1000 nm is epitaxially grown on the conductive GaN substrate, with a Si doping concentration of 3 × 10⁻⁶. 18 cm -3 An n-type GaN collector region with a thickness of 500 nm is epitaxially grown on the n⁺-type GaN secondary collector region, with a Si doping concentration of 1×10⁻⁶. 17 cm -3 A 70 nm thick p-type GaN base region is epitaxially grown on the n-type GaN collector region, with a Mg doping concentration of 3 × 10⁻⁶. 18 cm -3 .
[0093] The tunnel junction layer is continuously epitaxially formed on a p-type GaN base region. A 20 nm thick p++ type GaN layer with a Mg doping concentration of 1 × 10⁻⁶ is epitaxially grown on the p-type GaN base region. 20 cm -3 The p++ type GaN layer has an epitaxial growth of 5 nm thick In. 0.3 Ga 0.7 N auxiliary tunneling layer; the In 0.3 Ga 0.7 A 10 nm thick n++ type GaN layer is epitaxially grown on the N-assisted tunneling layer, with a Si doping concentration of 1×10⁻⁶. 20 cm -3The p++ type GaN layer, In 0.3 Ga 0.7 The N-type auxiliary tunneling layer and the n++ type GaN layer together constitute the tunnel junction layer, wherein the In 0.3 Ga 0.7 The N-auxiliary tunneling layer is located between the p++ type GaN layer and the n++ type GaN layer.
[0094] The AlGaN graded layer is epitaxially formed on the n++ type GaN layer. The AlGaN graded layer is Al x Ga 1-x The N-layer has a thickness of 20 nm and a Si doping concentration of 1 × 10⁻⁶. 19 cm -3 Along the epitaxial growth direction, the Al mole fraction x increases linearly from 0 near the n++ type GaN layer to 0.15 near the n-type AlGaN emitter region; viewed from the device cross-section, the Al mole fraction x decreases linearly from 0.15 near the n-type AlGaN emitter region to 0 near the n++ type GaN layer. A 150 nm thick n-type Al layer is epitaxially grown on the AlGaN graded layer. 0.15 Ga 0.85 N-emitting region, Si doping concentration is 1×10⁻⁶ 19 cm -3 .
[0095] A SiO2 hard mask layer was deposited on the epitaxial wafer surface using plasma-enhanced chemical vapor deposition (PECVD). The SiO2 hard mask layer was 250 nm thick, and the deposition temperature was 300 °C. The active region pattern was defined using ultraviolet lithography. The photoresist spin coating speed was 4000 r / min, the spin coating time was 40 s, the pre-baking temperature was 95 °C, and the pre-baking time was 90 s. After exposure, development was performed for 60 s to form the active region lithographic pattern.
[0096] The SiO2 layer in the exposed area was removed using CF4 / O2 reactive ion etching (RIE) at a flow rate of 40 sccm, an O2 flow rate of 5 sccm, a RIE power of 100 W, and an etching time of 3 min. Residual SiO2 was removed using a buffered oxide etchant with a wet etching time of 60 s. The unetched SiO2 was used as a hard mask for subsequent etching of the Group III nitride mesa.
[0097] The active mesa of the device was etched using a Plasma-Therm SLR 770 ICP-RIE system. The etching gases were BCl3 / Cl2, with a BCl3 flow rate of 20 sccm and a Cl2 flow rate of 5 sccm. The ICP power was 300 W, the RIE power was 50 W, and the chamber pressure was 5 mTorr. The mesa etching depth was set to 775 nm, ensuring the etched region penetrated the n-type AlGaN emitter region, the AlGaN gradient layer, the n++ type GaN layer, and the In layer. 0.3 Ga 0.7 An N-type auxiliary tunneling layer, a p++ type GaN layer, a p-type GaN base region, and an n-type GaN collector region are formed, and an n+ type GaN secondary collector region is exposed to form the collector contact region.
[0098] The emitter and base stripe structures are defined using a second photolithography process. Each emitter stripe is 3 μm long and 1.4 μm wide, with a total of 9 emitter stripe regions in the device; the spacing between adjacent emitter stripe regions and the base contact region is 0.3 μm. Separation etching of the emitter and base is performed using a low-power BCl3 / Cl2-based ICP-RIE process, with a BCl3 flow rate of 20 sccm, a Cl2 flow rate of 5 sccm, an ICP power of 40 W, a RIE power of 5 W, and a chamber pressure of 5 mTorr. This etched region is located on both sides of the emitter region, with an etching depth of 170 nm, used to remove the n-type AlGaN emitter region and the AlGaN gradient layer, and to expose the n++ type GaN layer in the tunnel junction to form the base contact window. The etching depth is controlled by pre-calibrated etching rate and etching time, allowing over-etching to not exceed 5 nm.
[0099] The emitter, base, and collector metals were defined using the same photolithography process. The emitter metal was positioned above the n-type AlGaN emitter region, the base metal was positioned on both sides of the emitter region and in contact with the exposed n++ type GaN layer, and the collector metal was positioned in the exposed n+ type GaN secondary collector region. The metal electrodes were deposited using electron beam evaporation, with an Al / Ni / Au stack, where the Al thickness was 20 nm, the Ni thickness was 20 nm, and the Au thickness was 100 nm. After metal deposition, acetone was used for lift-off to form the emitter, base, and collector patterns. The metal-lifted samples underwent rapid thermal annealing in a N2 atmosphere at 650 °C for 30 s to improve the ohmic contact characteristics of the n-type contact region.
[0100] An Al2O3 passivation layer was deposited on the device surface using atomic layer deposition (ALD). The precursors for the Al2O3 passivation layer were trimethylaluminum and deionized water. The deposition temperature was 200 °C, and the deposition thickness was 100 nm. The Al2O3 passivation layer covered the mesa sidewalls, the emitter-base spacer region, and the exposed semiconductor surface. It was used to reduce leakage current and recombination losses caused by etching the sidewall surface states and to serve as an insulating layer between the pad metal and the semiconductor surface.
[0101] The contact holes are defined using a third photolithography process, and the Al2O3 passivation layer is opened by buffered oxide etching solution or chlorine-based dry etching to expose the emitter, base, and collector metal regions. The pad metal is deposited using magnetron sputtering; the pad metal is Ni and has a thickness of 200 nm. After stripping, the pad metal forms emitter, base, and collector pads, resulting in a GaN-based HBT device with synergistic control of the AlGaN graded layer and tunnel junction.
[0102] In the device prepared in this example, the emitter forms an electrical contact through an n-type AlGaN emitter region, the base forms an electrical contact with the tunnel junction layer through an exposed n++ type GaN layer, and the collector forms an electrical contact through an n+ type GaN secondary collector region. The device employs a 9-strip emitter structure, each strip being 3 μm long and 1.4 μm wide, with a strip spacing of 0.3 μm between the emitter and base. This structure utilizes n++ / In... 0.3 Ga 0.7 The N / p++ tunnel junction enables electrical coupling to the p-type GaN base region, avoiding the direct formation of a low-resistance p-type ohmic contact on the p-type GaN base region. At the same time, the band transition from the emitter region to the tunnel junction region is improved through a 20 nm AlGaN linearly graded layer.
[0103] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0104] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction, characterized in that, include: The following layers are arranged from bottom to top: secondary collector region, collector region, base region, tunnel junction layer, AlGaN graded layer, and emitter region; The tunnel junction layer comprises a heavily doped p-type GaN layer and a heavily doped n-type GaN layer, wherein the heavily doped p-type GaN layer is closer to the base region, and the heavily doped n-type GaN layer is closer to the AlGaN gradient layer; the doping concentration of both the heavily doped p-type GaN layer and the heavily doped n-type GaN layer is 1×10⁻⁶. 19 cm -3 Up to 5×10 20 cm -3 ; The Al composition in the AlGaN graded layer decreases from the emitter region to the base region.
2. The GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction according to claim 1, characterized in that, An emitter is disposed above the emitter region; base electrodes are disposed on both sides of the emitter region and are in electrical contact with the heavily doped n-type GaN layer in the tunnel junction layer; a collector electrode is disposed on the side of the collector region or the secondary collector region.
3. The GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction according to claim 1, characterized in that, The emitter region is an n-type AlGaN layer with a thickness of 50~300 nm and a doping concentration of 5×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 .
4. The GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction according to claim 1, characterized in that, The base region is a p-type GaN layer with a thickness of 30~150 nm and a doping concentration of 5×10⁻⁶. 17 cm -3 ~8×10 18 cm -3 .
5. The GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction according to claim 1, characterized in that, The secondary collector region is an n+ type GaN layer with a thickness of 0.5~2 μm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 The current collector region is an n-type GaN layer with a thickness of 200~1000 nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 18 cm -3 .
6. The GaN-based HBT device with synergistic modulation of AlGaN graded layer and tunnel junction according to claim 1, characterized in that, The AlGaN gradient layer is Al x Ga 1-x The N-gradient component layer, where x represents the mole fraction of Al, the maximum value of the mole fraction of Al x does not exceed 30%, and the mole fraction of Al x decreases to 0 near the tunnel junction.
7. The simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layer and tunnel junction as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Establish a structural model of a GaN-based HBT device in the simulation platform, set the material type, thickness, and doping parameters of each region in the structural model, and set the collector, base, and emitter. S2, Introduce a semiconductor physical model that includes a polarization effect model and an interband tunneling model into the structural model; S3. Apply a bias voltage to the structural model to perform voltage scan simulation and extract the corresponding device electrical characteristic parameters, band distribution and electric field distribution. S4, change at least one parameter among the Al composition distribution of the AlGaN gradient layer, the thickness or doping concentration of the heavily doped p-type GaN layer and the heavily doped n-type GaN layer, repeat S3 to obtain multiple sets of simulation results after changing the parameters, and select the parameters that meet the preset conditions as the optimized device structure parameters.
8. The simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layer and tunnel junction according to claim 7, characterized in that, The semiconductor physical model also includes: an incomplete ionization model for simulating the ionization characteristics of acceptor impurities in the base region, and a mobility degradation model, an SRH recombination model, and an Auger recombination model for describing carrier transport characteristics.
9. The simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layer and tunnel junction according to claim 7, characterized in that, The process of applying a bias voltage to the structural model for voltage scanning simulation includes: fixing the voltage between the collector and the emitter, and scanning the voltage between the base and the emitter; the electrical characteristic parameters of the device include: base current, collector current, and current gain.
10. The simulation optimization method for GaN-based HBT devices with synergistic control of AlGaN graded layer and tunnel junction according to claim 7, characterized in that, The preset conditions are: the collector current of the structural model is greater than a preset current threshold, and the peak electric field inside the structural model does not exceed a preset breakdown electric field threshold.