A review of gallium oxide-based power Schottky barrier diodes

Usually, an excellent Ohmic contact has low or even no SBHs, and exhibits a linear current−voltage curve, which minimizes the energy consumption and also prevents thermal effects caused by contact resistance. This is especially important due to the intrinsic low thermal conductivity of Ga₂O₃. Hence, a superior Ga₂O₃ Ohmic contact is a prerequisite for achieving a high-performance device. Lee et al [57] described the interfacial reaction of Ti/Ga₂O₃ in detail and confirmed that Ti/Ga₂O₃ has a good Ohmic contact. Currently, most of the Ga₂O₃ device articles use Ti metal as the Ohmic contact [18, 37, 58–62]. Based on this, several effective methods have been used to further reduce the Ohmic contact resistance, such as doping [63], surface treatment [64], plasma treatment [65], etc. A recent report shows that Ga₂O₃ with heavy (n⁺) Si-doped (∼1.8 × 10²⁰ cm⁻³) exhibits a record low Au/Ti/Ga₂O₃ (n⁺) contact resistance of 80 mΩ mm with specific contact resistivity of 8.3 × 10⁻⁷ Ω cm² [63]. Jeong et al demonstrated Ohmic behavior with specific resistivity of 2.0 × 10⁻³ Ω cm² and contact resistance of 0.8 Ω m by using CF₄ plasma for surface treatment without any post-thermal annealing [64]. Massabuau et al reported the impact of annealing temperature on the Ohmic contact between Ti and α-Ga₂O₃ and demonstrated that 450 °C is optimal due to the fast diffusion channel provided at this temperature [65]. Therefore, Ti metal is the most promising and dominant Ohmic contact metal material for now.

The Schottky diode is a majority-carrier-conducting device without the problem of minority carrier lifetime and reverse recovery, which is completely different to the reverse recovery of p–n junction diode caused by the recombination of electrons and holes. In addition, the SBH is lower than the p–n junction barrier. This advantage gives Schottky diodes a high switching frequency and a lower forward voltage.

In the early stage, most of the reports focused on the electronic properties of Ga₂O₃ SBD devices using metal−semiconductor Schottky contact structure without terminal design, surface passivation and other optimized processes. In this section, we briefly sum up the electronic behavior of Ga₂O₃ with various Schottky metals. There have been studies of Schottky contacts on different Ga₂O₃ orientation surfaces to analyze their characteristics, such as barrier height (SBH) and ideality factor (n). The characteristic performance of Schottky barriers is generally analyzed by I–V, CV curves. The details of different studies are summarized in table 2. The selection of a suitable Schottky metal electrode is a cornerstone for future studies of Ga₂O₃ Schottky SBD device performance. However, we are also aware that different interface characteristics and contact environments can affect the Schottky barrier, which requires specific analysis in each case. Various post-treatments are intended to reduce the interface states and to improve M−S contacts, attaining high performance with lower on-resistance (R_ON) and higher breakdown voltage (V_BR).

For Ga₂O₃-based SBD devices, the initial devices were prepared with only front-side Schottky contacts and backside Ohmic contacts on a single crystal to study the device performance [37, 73, 75, 77]. The schematic of the device is shown in figure 3(a). An initial report by Sasaki et al [40] proposed the use of a Pt circular electrode Schottky junction to fabricate Pt/Ga₂O₃ SBD on single-crystal β-Ga₂O₃ (010) substrates. This device, using simple device structures and processing techniques without terminal structures and other processes demonstrates ideal coefficients close to 1.0. The SBH between Pt and β-Ga₂O₃ was 1.3–1.5 eV with a high breakdown voltage of about 150 V. These results can be attributed to the high crystal quality of Ga₂O₃ substrates and show the great potential of Ga₂O₃ power devices for future applications. These were further developed by adding an epitaxial layer to those early SBD structures. Pearton et al [78] reported that β-Ga₂O₃ SBDs were fabricated in a vertical structure on Si-doped epitaxial layers (10 µm, n ≈ 4 × 10¹⁵ cm⁻³) on Sn-doped bulk Ga₂O₃ substrates, which includes Ni/Au front Schottky contacts and Ti/Au back Ohmic contacts. The schematic of the device is shown in figure 3(b). It shows the device with V_BR values up to 1600 V (20 µm diameter contacts) and ∼250 V for rectifiers (0.53 mm diameter), and R_ON values were 25 and 1.6 mΩ cm² respectively, leading to a BFOM for the latter of approximately 102.4 MW cm⁻². The results show that Ga₂O₃ SBDs without additional structures and edge terminals exhibit high performance based on high-quality substrates and epitaxy. The latest work presents a high-performance Ni/(001) β-Ga₂O₃ regular SBD without edge termination with a high PFOM of 1.32 GW cm⁻² and a maximum V_BR of 1720 V by suppressing the formation of donor-like impurities accumulated on the surface [79]. Hence, Ga₂O₃ SBD has great potential for high-voltage applications.

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Furthermore, the development of α-Ga₂O₃ SBD has achieved great success. In 2015, FLOSFIA, INC. [68] used mist CVD epitaxy to grow 8 μm thick n⁺ epitaxial layer for Ohmic contact and n⁻ epitaxial layer for Schottky contact on sapphire substrate and then removed the sapphire substrate to make α-Ga₂O₃ SBD, as shown in figure 4(a). The device showed a V_BR of 270 V, n of 1.1 and a current on-off ratio of 10⁶. The poor performance is caused by the current density limitation of the epitaxial layer. Afterwards, the conductivity of the α-Ga₂O₃ epitaxial layer was adjusted by controlling the doping of Sn to improve the performance of the SBD [80]. Two types of SBD were prepared, SBD 1 and SBD 2, of which SBD 1 with an n-epitaxial layer thickness of 430 nm exhibited low on-resistance (0.1 mΩ cm²) and V_BR of 531 V; SBD 2 with an n^- epitaxial layer thickness of 2580 nm exhibited a high breakdown voltage (855 V) and R_ON of 0.4 mΩ cm², as shown in figures 4(c) and (d). Both SBDs have an n⁺ layer of 3–4 μm without edge termination, passivation or FP structure. The thermal resistance of the TO220-packaged α-Ga₂O₃ SBD device was found to be as small as 13.9 °C W⁻¹. This value is comparable to that of a commercial SiC SBD device (12.5 °C W⁻¹). This TO220-packaged α-Ga₂O₃ SBD also showed the fastest recovery compared to a commercial SiC SBD and a Si p−n junction diode [21]. This safe, low-cost and energy-efficient mist CVD epitaxial technology offers tremendous advantages for α-Ga₂O₃ power device applications. The comparison of electric performances for basic structure Ga₂O₃ SBDs are summarized in table 3.

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While there has been tremendous development of Ga₂O₃ devices, there are still many ways to improve device performance. Simple processes offer advantages in terms of industrialization and device reliability. Therefore, we want the fabrication process of Ga₂O₃-SBD to be as simple as possible. Ion-implantation terminal edge-termination technology can create a high-resistance region, thus forming effective electron isolation around the anode edge region. This effectively relieves the electric field crowding effect by reducing the peak value, as shown in figure 5(a). Therefore, the reported method of implementing ion-implanted edge termination, is a well-proven and effective way to increase the device performance of Ga₂O₃-SBD. Zhou et al [83] reported that Mg-implanted edge-termination processing is a very simple but useful technique to improve the V_BR of the vertical β-Ga₂O₃ SBD. Compared to the device without Mg-implanted edge-termination treatment, the breakdown voltage of β-Ga₂O₃ SBD is substantially increased from 500 to 1050 V. In addition, it was shown that a high power figure of merit (PFOM) of 0.47 GW cm⁻² and low R_ON of 5.1 mΩ cm² were realized at an epitaxial layer thickness of 10 µm with a diode radius of 90 µm. There is a slight increase in V_BR when the anode radius is decreased and a V_BR of 1.65 kV is demonstrated at R = 40 and 65 μm. To verify the effect of Mg-implanted edge termination on the device, technological computer-aided design (TCAD) simulations were carried out on the device with and without edge termination. The results showed the effectiveness of the implanted edge termination to mitigate the peak electric field at the anode edge and hence an enhanced breakdown voltage is expected. A similar approach is used to increase the breakdown voltage using an N-implanted guard ring [84]. The reverse leakage current is several orders of magnitude lower than the Mg-implanted edge-termination β-Ga₂O₃ SBD and the V_BR by up to 860 V. In addition, the Ga₂O₃ SBD was fabricated by using argon-implantation edge-terminated technology to form the high-voltage resistance performance at the periphery of the anode contacts [85, 86]. The results indicate great promise of vertical β-Ga₂O₃ SBDs for high-voltage and fast switching applications. The most recent reports on ion implantation to achieve high-performance vertical β-Ga₂O₃ SBD were based on a self-aligned beveled fluorine plasma treatment (BFPT) edge-termination structure [87]. Due to the strong electronegativity of fluorine ions, the introduction of numerous F negative charges will relieve the electric field pressure and therefore reduce reverse leakage and increase the breakdown voltage. The results indicate V_BR up to 1050 V with a relatively low R_ON of 2.5 mΩ cm², which is an excellent performance to date using a simple, effective and versatile edge-termination technique for self-aligned BFPT. This simple, easy-to-control edge-termination technique offers great advantages for fabricating high-quality, high-performance Ga₂O₃ SBD devices.

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Wang et al [88] reported a novel edge-termination process to achieve a high-performance β-Ga₂O₃ vertical SBD by using thermally oxidized termination. The schematic of the device structure is shown in figure 5(b). The high-temperature thermal oxidation treatment reduces the electron concentration in the anode edge region and effectively suppresses the peak electric field at the device edge. For oxidation-terminated SBD annealed at 400 °C, the V_BR of β-Ga₂O₃ SBD increases from 380 to 940 V, but the R_ON only increases from 2.9 to 3.0 mΩ cm². The device demonstrates a PFOM (V_BR ²/R_ON) as high as 295 MW cm⁻². The decrease in the electron concentration in the oxidized region can effectively reduce the peak electric field at the Schottky contact edge. The simulation results of the lateral electrostatic field indicate that the thermally oxidized termination shows a new way to improve the breakdown characteristics of β-Ga₂O₃ SBD. Recently, Hao Yue's team reported a new terminal structure approach by incorporating the etched and filled SiO₂ layer process to obtain a record-high breakdown voltage of 6 kV and a low R_ON of 3.4 mΩ cm² for β-Ga₂O₃ SBD [89]. The device schematic is shown in figure 6. This simple and effective terminal structure allows Ga₂O₃ SBDs to be pushed to higher-voltage applications in power electronics.

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In general, the edge-termination technique is the simplest, most effective and most versatile to achieve a termination cutoff at the edge of the device, which effectively increases V_BR and improves electrical properties at the electrode, by reducing the edge electron concentration and alleviating peak electric field. Therefore, this is greatly advantageous in preparing high-quality Ga₂O₃ SBD devices by using the simplest process possible. The comparison of electrical performances for β-Ga₂O₃ SBDs with edge termination (ET) are summarized in table 4.

The effect of long-term Ga₂O₃ SBD device performance reliability due to damage to the lattice by ion implantation has not yet been studied. We need to find more ways to address the premature breakdown voltage of Ga₂O₃ SBDs due to the presence of a peak electric field at the electrode edges. Field-plated (FP) technology is widely used in AlGaN/GaN HEMTs, SiC, GaN and other power devices to improve the reverse breakdown voltage and electron distribution characteristics [92–97]. FP techniques have the advantage of a simpler and more controllable manufacturing process, and the fact that they avoid the increased leakage associated with ion implantation, ion implantation and thermal oxidation can create uncontrollable ion diffusion problems. The FP structure needs to be built on a dielectric layer, and the selection of a suitable dielectric layer will also determine device performance [62, 98]. The initial report on Ga₂O₃ field-plated SBDs (FP-SBDs) indicated that they were successfully fabricated on a Si-doped n⁻ Ga₂O₃ drift layer grown by HVPE on a Sn-doped n⁺ Ga₂O₃ (001) substrate [99]. The L_FP = 20 μm FP Schottky anode electrodes were fabricated by realignment to the SiO₂ windows, as shown in figure 7(a). The results show that R_ON was estimated to be 5.1 mΩ cm² in a high V_BR of 1076 V, and the simulated maximum electric field below the anode foot edge was 5.1 MV cm⁻¹, as shown in figure 7(b). This is much larger than the theoretical limits for SiC and GaN and comparable to the extracted breakdown field for lateral Ga₂O₃ MOSFETs [100].

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Yang et al are conducting a series of studies on Ga₂O₃ FP technology and comparing the differences in FP SBD with different dielectric layers [62, 101]. They initially prepared a Ga₂O₃ FP SBD with an electrode area of 0.01 cm² on a 10 µm thick, lightly doped drift layer (1.33 × 10¹⁶ cm⁻³) on heavily doped (3.6 × 10¹⁸ cm⁻³) substrates [102]. The device can achieve a forward current of 1 A and a reverse breakdown voltage of 650 V with a power density FOM above 20 MV cm⁻², which is well within the parameters of a power rectifier. Later, a new Ga₂O₃ FP SBD was prepared in A 20 μm thick, lightly doped (n = 2.1 × 10¹⁵ cm⁻³) epitaxial layer on a conduction (n = 3.6 × 10¹⁸ cm⁻³) substrate with a 150 μm diameter device (area = 1.77 × 10⁻⁴ cm⁻²) [103]. The corresponding devices have further improved performance with breakdown voltages of up to 2300 V, as shown in figure 8. The on-state resistance (R_ON) for these devices was 0.25 Ω cm², leading to an FOM (V_BR ²/R_ON) of 21.2 MW cm⁻² and can be adjusted to a voltage range of 1400–2300 V by changing the electrode size. In addition, a recovery time test with the device in the circuit showed a recovery time of only 20 ns from +2 to −2 V. In the future, the main focus will be on reducing the R_ON while continuing to increase the withstand voltage. To verify the application of the device in the circuit, the team prepared a switching circuit for high breakdown voltage Ga₂O₃ vertical Schottky rectifiers [104]. Based on this Ga₂O₃ FP SBD design, it can operate at switchable voltages of up to 900 V. Furthermore, a high-performance output current of 33.2 A and a PFOM (V_BR ²/R_ON) of 4.8 MW cm⁻¹ were achieved through the array structure consisting of 21 Ga₂O₃ FP rectifiers [60]. These results are another milestone for Ga₂O₃ towards its path for promising high-power electronic device applications since rectifiers are needed in inverter modules for power conversion systems.

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Previously, beveled field-plate (BFP) Ga₂O₃ SBDs were also reported by Joshi et al [20] and Allen et al [105]. The latter reported better performance with the FP SBD, which consists of spin-on-glass and plasma-enhanced chemical vapor deposited SiO₂, to fabricate a very small bevel angle (∼1°) in the mesa and FPs. The BFP SBD greatly promotes the electric field distribution at device edges, which results in a V_BR of 1100 V, a peak electric field of 3.5 MV cm⁻¹,and a BFOM of 0.6 GW cm⁻². Xia et al [106] also investigated the performance of FP Ga₂O₃ SBDs at different temperatures, with reverse V_BR of 750 V at up to 600 K, 950 V at 500 K, and 1460 V at 400 K. Promising results of good protection against pressure and high-temperature operation were achieved. However, the FP-SBD device with the highest reverse breakdown voltage reported so far is a lateral structured device [107]. A high-performance lateral FP β-Ga₂O₃ SBD on a sapphire substrate with reverse V_BR of more than 3 kV and a low DC R_ON of 24.3 mΩ cm² at an anode-cathode spacing (L_AC) of 24 μm is achieved. Overall, the external FP structure further improves the device's reverse breakdown voltage and exhibits a higher PFOM than the edge-termination structure.

In brief, FP structure techniques have been widely used in the fabrication of Ga₂O₃ power devices due to their relatively simple preparation process as well as the introduced external defects that cause increased reverse leakage. In order to implement the advantages of this FPe technology, more suitable high-dielectric materials are needed. In this way, FPs effectively reduce the peak value of the electric field at the edges of the channel. This will achieve a high breakdown voltage in Ga₂O₃ power devices. The comparison of electric performances for β-Ga₂O₃ SBDs with field-plated (FP) structure are summarized in table 5.

For conventional SBDs, the maximum electric field is located at the Schottky contact with surface higher reverse leakage current density at reverse bias, which means that limiting the electric field near the Schottky contact surface is necessary [109]. At present, various techniques, such as edge termination and FP structure, have been utilized to increase the V_BR of Ga₂O₃ SBDs by slowing down the peak electric field at the edge of the electrode. However, a large reverse leakage current is present, under a large reverse electric field, at the Schottky metal–semiconductor interface with a single junction barrier [110]. To alleviate the leakage constraint and the distribution of the maximum field strength from the Schottky contact surface to the inside of the device body, many power devices use junction-barrier-Schottky (JBS) structures with p–n junctions to reduce the electric field near the Schottky contact interface due to the charge-coupling effect [111]. However, since the problem of Ga₂O₃ p-type technology has not been resolved, the Ga₂O₃ SBD will not be able to adopt the JBS structure either. Trench MOS structure of the SBD will be a good choice, and the MOS junction on the sidewall will replace the p–n junction in the JBS [112–114]. Here, the introduction of a metal-insulator-semiconductor (MOS/MIS) junction barrier structure not only increases the V_BR with trench termination, but also effectively reduces leakage with reduced surface electric field (RESURF) techniques.

Sasaki et al [115] first reported the Ga₂O₃-Trench-MOS SBD. The SBD was fabricated on a 7 μm (001) epitaxial layer (n = 6 × 10¹⁶ cm⁻³) grown by halide vapor phase epitaxy (HVPE) on a single-crystal Ga₂O₃ substrate. Compared to the normal SBDs (R_ON = 2.3 mΩ cm²), the R_ON (2.9 mΩ cm²) is slightly higher, probably due to the reduced current path in the trench-MOS structure. The trench-MOS SBD has a leakage current several orders of magnitude smaller than the normal SBD, indicating that the trench MOS structure can effectively reduce the reverse leakage current. The device was tested for recovery characteristics by the double-pulse method [116]. It was confirmed that the trench MOS-Ga₂O₃-SBDs exhibit high speed and low loss recovery characteristics.

Many processing conditions affect the performance of the device, such as the appropriate thickness of the epitaxial layer, doping concentration, fin width, trench width, etc, which determine its final performance. In 2018, at the 76th Device Research Conference, it was reported that a trench-MIS device on 10 µm Si-doped n-Ga₂O₃ epitaxial layer grown on f 620 µm (001) n-type substrate, exhibited V_BR of 1.5 kV with a ∼10⁴ times reduction in reverse leakage current compared to regular SBDs [117]. Increasing the doping concentration of the epitaxial layer results in an increase in the forward current and a decrease in V_BR (1230 V) [118]. However, it maintains non-declining forward characteristics compared to regular SBD with trench structure, indicating that the trench structure has a significant effect in reducing the surface electric field and effective MOS junction barrier height. Figure 9(a) shows the schematic cross-section of the trench SBDs with fin widths of 2, 3 and 4 μm, and trench depth of 2 μm, where the trench region uses MIS (MOS)-junction structure. As shown in figure 9(b), the electric field near the top surface is effectively reduced by the trench-MIS structure, and the RESURF effect is more pronounced with a smaller fin width. The trench depth is further reduced to 1.5 μm, and after dry etching in BCl₃/Ar, the trench is then wet treated to remove the dry etch-induced damage and round the trench corners, resulting in devices with breakdown voltages of up to 2440 V and leakage current densities below 1 μA cm⁻² [119].

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To further improve the reverse breakdown voltage of Ga₂O₃ SBDs, Huang et al [120] used TCAD simulations for optimization to investigate the effect of structural parameters on V_BR and FOM based on the electric field distribution and edge effects at the bottom of the trench. As shown in figure 10, an optimized parameter of W = 4 μm and R = 1.2 μm, a maximum V_BR of over 3 kV and a FOM of 2 GW cm⁻² are predicted. As the structural patterns of Ga₂O₃ SBDs develop, and the breakdown mechanism is better understood, experiments are considered to adopt some composite structures to further improve the performance of the devices. An FP-trench SBD was fabricated with a double dielectric layer, and the trench structure was adapted with a fin width of 1 µm and a fin height of 1.1 µm [121]. From a simulation analysis of the FP-trench structure with a surface, it is shown that the FP largely eliminates the peak electric field at the anode edge and moves the peak electric field location to the outer edge of the FP. Compared to previous reports (V_BR = 2400 V), this further increases the V_BR of the SBD to 2.48 kV and achieves a FOM value of 0.78 GW cm⁻² by pulse testing. By further optimizing the previous device, both the fin and the trench width are designed to be 1 µm, together with the edge FP structure [122]. The device exhibits a high V_BR of 2.89 kV with a record high BFOM value of 0.80 (0.95) GW cm⁻², among all Ga₂O₃ power devices reported so far. In general, the trench-MOS barrier structure effectively reduces the electric field in the plane, resulting in a much lower reverse leakage and a higher breakdown voltage, which compensates for the material limitations that make it difficult to implement the p-type. Next, with a suitable edge-termination structure, it is believed that the performance of the device can be further improved.

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Obviously, the trench-MOS structure of Ga₂O₃ is the preferred mode in kilovolt-level SBD devices with the base material p-type unresolved. The RESURF effect in trench-MOS structure not only improves the reverse leakage very well, but also improves the breakdown voltage to a great extent. However, there are still some details that need to be further investigated to reach an optimal device performance, such as optimization of the trench structure, suitable high-k dielectric layers and other process treatments. Together with other end-processing and FP structures, Ga₂O₃ SBD will have a huge potential in power devices. The comparison of electric performances for β-Ga₂O₃ SBDs with trench are summarized in table 6.

Although the unipolar Ga₂O₃ SBD device has been significantly developed, the difficulty of p-type doping has limited the development of Ga₂O₃ p–n power diodes. Early reports use other p-type materials to construct Ga₂O₃ p–n HJDs to achieve Ga₂O₃ bipolar power devices [125–127]. At this point, the heterojunction p-Cu₂O/Ga₂O₃ diode already exhibits a very high breakdown voltage of 1.49 kV and has a very high forward current of over 100 A cm⁻² [127]. Considering that the narrow band gap of p-Cu₂O limits its potential, the p-NiO/Ga₂O₃ diodes also exhibit a high breakdown field strength of 1059 V and have an ultra-low reverse leakage current of below 1 μA cm⁻² [128]. Ye et al [129] constructed a double-layered NiO/Ga₂O₃ vertical p–n HJD with different hole concentrations, as shown in figure 11. The device exhibits a very low leakage current and has a high rectification ratio of over 10¹⁰ (at ±3 V) even when operated at a temperature of 400 K, indicating its excellent thermal stability and operation capability at high temperatures. The breakdown voltage has also greatly improved to 1.86 kV with R_ON of 10.6 mΩ cm².

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The devices have been tested on circuits up to 12 A/70 A and have achieved ultra-fast switching performance with a reverse recovery time of 11 ns at a surge-current of 45 A [130]. This gives the device significant potential for high-voltage, high-frequency applications. In addition, some studies have shown that the annealed NiO/Ga₂O₃ p–n junctions have a very low defect density and that the performance of the diode is significantly improved [131]. As the research progressed, the first vertical β-Ga₂O₃ JBS diode was prepared, using the thermally oxidized p-type NiO to compensate for the absence of the p-type β-Ga₂O₃ [132]. The JBS diode exhibits a high electrical performance with V_BR of 1715 V and R_ON of 3.45 mΩ cm², yielding a BFOM (V_BR ²/R_ON) of 0.85 GW cm⁻², which is the highest direct-current FOM value among all β-Ga₂O₃ diodes. Meanwhile, a large-size JBS diode with an area of 1 × 1 mm² shows forward current I_F and V_BR of 5 A/700 V, which is also the best power factor (FOM = 64 MW cm⁻²) among all published results about large-area Ga₂O₃ diodes. Next, in order to carry out a comparative study, five types of P-NiO/Ga₂O₃ heterojunction power SBDs with different configurations were fabricated, which include the heterojunction p-NiO/Ga₂O₃ JBS uniform field-limited ring width/spacing of 2 μm (HJBS-2 μm), HJBS-3 μm, Ni/Ga₂O₃ SBD with a uniform field limiting rings (SBD-FLR), NiO/Ga₂O₃ p–n HJD and Ni/Ga₂O₃ bare SBD, as shown in figure 12. HJBS-2 μm achieves a maximum V_BR of 1.89 kV and an R_ON of 7.7 mΩ cm², yielding a high FOM of 0.46 GW cm⁻². At the same time, the reverse leakage mechanism of HJBS is revealed to be Poole–Frenkel emission through localized trap states [133]. Recently, they have made a new breakthrough by reporting a novel composite terminal structure, including a p-type NiO junction termination extension and a small-angle BFP, which shows a much higher V_BR of 2410 V and a low R_ON of 1.12 mΩ cm², yielding a record-high power FOM value of 5.18 GW cm⁻² [134]. In addition, p-GaN is also a good choice for constructing GaN/Ga₂O₃ p–n diodes with a low lattice mismatch of 2.6% [135], but there is little experimental research on GaN/Ga₂O₃ p–n power devices due to the fabrication limitations of GaN on Ga₂O₃. However, Nandi et al used TCAD simulations to propose a calibration model for the p-GaN/n-Ga₂O₃ junction barrier Schottky diode (JBSD) in Silvaco ATLAS. The JBSD provides better performance in terms of breakdown with a highest reverse breakdown voltage of 1890 V and a best switching time of 9.2 ns [136]. In fact, the heterojunction p–n also shows good performance and will be further developed when the p-type Ga₂O₃ problem is not resolved. The comparison of electric performances for β-Ga₂O₃ SBDs with p-n heterojunction structure are summarized in table 7.

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In this section, we introduce several different structures of Ga₂O₃ SBDs and detail a few of the current best-performing devices. At present, some of the most basic devices have breakdown voltages close to 1000 V and may play an important role in the low and medium power market. However, to further increase the device's withstand voltage, other structures must be used, such as FPs, trench-MOS, etc. In addition, high-quality materials are an important part of improving device performance. Therefore, the combination and optimization of all mentioned factors can lead to further improvement of the performance of Ga₂O₃ SBD. With the development of Ga₂O₃ devices, the following improved points should be focused on.

4.6.1. High-quality material base.

4.6.2. Contact interface of metal/Ga₂O_3.

4.6.3. Device structure optimization.

4.6.4. Device thermal management.

4.6.5. Device reliability.