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The fabrication and switching characteristics of large diameter (1mm) Ga2O3 heterojunction rectifiers with bilayers of NiO as the p-type layer are reported. The band alignment shows this is a staggered-gap system. Selective wet and dry etching was developed to allow fabrication of vertical geometry heterojunction rectifiers. A forward current of 2.5 Amperes was achieved, with a reverse breakdown voltage of 2.7 kilovolts. The on/off ratio was above 108 over a broad range of switching voltages, with a measurement-limited reverse recovery time of 100 nanoseconds.

Patterning of NiO/Ga2O3 heterojunctions requires development of selective wet and dry etch processes. Solutions of 1:4 HNO3:H2O exhibited measurable etch rates for NiO above 40 °C and activation energy for wet etching of 172.9 kJ.mol−1 (41.3 kCal.mol−1, 1.8 eV atom−1), which is firmly in the reaction-limited regime. The selectivity over β-Ga2O3 was infinite for temperatures up to 55 °C. The strong negative enthalpy for producing the etch product Ga(OH)4 suggests HNO3-based wet etching of NiO occurs via formation and dissolution of hydroxides. For dry etching, Cl2/Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800 Å.min−1, with maximum selectivities of β-Ga2O3. The ion energy threshold for initiation of etching of NiO was ∼55 eV and the etch mechanism was ion-driven, as determined the linear dependence of etch rate on the square root of ion energy incident on the surface.

There is increasing interest in the alpha polytype of Ga2O3 because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga2O3 remains type II, staggered gap for annealing temperatures up to 600°C, showing that this a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga2O3. The magnitude of both the conduction and valence band offsets increase with temperature up to 500°C, but then are stable to 600°C. For the as-deposited NiO/ α-Ga2O3 heterojunction, ΔEV=-2.8 eV and ΔEC= 1.6 eV, while after 600°C annealing the corresponding values are ΔEV=-4.4 eV and ΔEC= 3.02 eV. These values are 1-2 eV larger than for the NiO/β-Ga2O3 heterojunction.

NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 heterojunction lateral geometry rectifiers with diameter 50-100 µm exhibited maximum reverse breakdown voltages >7kV, showing the advantage of increasing the bandgap using the β-(Al x Ga1-x )2O3 alloy. This Si-doped alloy layer was grown by Metal Organic Chemical Vapor Deposition with an Al composition of ~21 %. On state resistances were in the range 50-2180 Ω.cm2, leading to power figures-of-merit up to 0.72 MW.cm-2. The forward turn-on voltage was in the range 2.3-2.5 V, with maximum on/off ratios >700 when switching from 5V forward to reverse biases up to -100V. Transmission line measurements showed the specific contact resistance was 0.12 Ω.cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based rectifier.

Background: Currently, the standard of treatment for trimalleolar (TM) fracture is osteosynthesis through open reduction and internal fixation (ORIF). This study assessed whether arthroscopically assisted reduction and minimally invasive surgery (AARMIS) can be an alternative surgical method for TM fractures. Methods: This retrospective cohort study included 49 patients with TM that were surgically treated. 27 patients received ORIF and 22 patients underwent AARMIS . At baseline, we recorded the patient’s demographic features, fracture pattern (AO-OTA and Haraguchi classification), and surgical method. For postoperative results, we examined the patient’s radiographic outcome, including time to union, quality of fracture reduction, as well as functional outcomes (American Orthopaedic Foot & Ankle Society ankle hindfoot score, ankle range of motion, and visual analog scale of pain) and perioperative complications. Results: At mean follow-up of 46.6[Formula: see text] (ORIF) and 36.4[Formula: see text] months (AARMIS), both groups had comparable radiographic outcomes. No significant difference in rates of early ankle OA were detected. In terms of functional outcome, VAS pain and AOFAS score at postoperative day 3, postoperative month 3, and at final follow-up were not different. In terms of range of motion, we did not find a significant difference in mean range of motion. Conclusion: Patients with TM fractures treated with AARMIS achieved satisfactory results and was not significantly different in radiographic and functional performance compared with ORIF. Level of Evidence: Level III, retrospective cohort study.

Blood testing is a crucial medical application. In this study, we applied Raman spectroscopy to test blood samples and obtained complete biological information, including the main components and compositions in these samples. Short-wavelength (532-nm green light) Raman scattering spectroscopy was conducted on samples of normal blood, abnormal blood in 3 types of preparation including whole blood, plasma, and serum, and the underlying information reflected by the biological characteristics detected in each sample type were analyzed. Raman spectroscopy results indicated that normal blood had high hemoglobin content, which suggests that hemoglobin is a major component of blood. Hemoglobin affects blood oxygen level. The characteristic peaks of hemoglobin were observed at 690, 989, 1015, 1182, 1233, 1315, and 1562–1649 cm−1. Analysis of plasma and serum samples indicated the presence of β-carotene, which exhibited characteristic peaks at 1013, 1172, and 1526 cm−1. In addition, surface-enhanced Raman spectroscopy was used to collect biological signals that are difficult to obtain in conventional Raman spectroscopy, including those of small molecules such as hormones, antibodies, and enzymes. Changes in biological information collected in this manner can be used as a basis for potentially diagnosing clinical diseases.

Vertical geometry NiO/β n-Ga2O/n+ Ga2O3 heterojunction rectifiers with contact sizes from 50 to 200 μm diameter showed breakdown voltages (VB) up to 7.5 kV for drift region carrier concentration of 8 × 1015 cm−3. This exceeds the unipolar 1D limit for SiC and was achieved without substrate thinning or annealing of the epi layer structure. The power figure-of-merit, VB2/RON, was 6.2 GW cm−2, where RON is the on-state resistance (9.3–14.7 mΩ cm2). The average electric field strength was 7.56 MV/cm, approaching the maximum for β-Ga2O3. The on–off ratio switching from 5 to 0 V was 2 × 1013, while it was 3 × 1010–2 × 1011 switching to 100 V. The turn-on voltage was in the range 1.9–2.1 V for the different contact diameters, while the reverse current density was in the range 2 × 10−8–2 × 10−9 A cm−2 at −100 V. The reverse recovery time was 21 ns, while the forward current density was >100 A/cm2 at 5 V.

NiO/β-Ga2O3 vertical rectifiers exhibit near-temperature-independent breakdown voltages (VB) of >8 kV to 600K. For 100 µm diameter devices, the power figure of merit (VB)2/ RON, where RON is the on-state...

Background: Adult acquired flatfoot deformity (AAFD) and hallux valgus (HV) are common foot and ankle deformities. Few studies have reported the changes in radiographic parameters of HV after reconstructive surgery for AAFD. This study aimed to evaluate the changes in radiographic parameters of HV and analyze the risk factors for increased HV after correction of AAFD. Methods: Adult patients with flexible AAFD who underwent similar bony procedures including medializing calcaneal osteotomy and Cotton osteotomy were included. Radiographic parameters were measured on weightbearing radiographs preoperatively, postoperatively, and at the final follow-up. Patients were divided into hallux valgus angle (HVA) increased and HVA nonincreased groups; logistic regression analysis was performed to identify risk factors affecting increased HV. Results: Forty-six feet of 43 patients were included. After AAFD reconstructive surgery, the tibial sesamoid position improved by 1 grade, but the HVA increased 4 degrees in average. Further, 21 of 46 feet (46%) showed an HVA increase ≥5 degrees immediately after AAFD correction surgery. Preoperative talonavicular coverage angle Conclusion: In this case series, using plain radiographs to measure standard parameters of foot alignment, we found the association between AAFD correction and HV deformity measures somewhat paradoxical. Correction of overpronation of the hindfoot and midfoot appears to improve the first metatarsal rotational deformity but may also increase HVA. A lower preoperative talonavicular coverage angle was associated with an increase of the HVA after surgery. Level of Evidence: Level IV, case series study.

NiO/β-(Al xGa1− x)2O3/Ga2O3 heterojunction lateral geometry rectifiers with diameter 50–100 μm exhibited maximum reverse breakdown voltages >7 kV, showing the advantage of increasing the bandgap using the β-(Al xGa1− x)2O3 alloy. This Si-doped alloy layer was grown by metal organic chemical vapor deposition with an Al composition of ∼21%. On-state resistances were in the range of 50–2180 Ω cm2, leading to power figures-of-merit up to 0.72 MW cm−2. The forward turn-on voltage was in the range of 2.3–2.5 V, with maximum on/off ratios >700 when switching from 5 V forward to reverse biases up to −100 V. Transmission line measurements showed the specific contact resistance was 0.12 Ω cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based rectifier.

Background:This retrospective study aimed to describe the techniques and results of distal metatarsal segmental shortening (DMSS) for the treatment of chronic irreducible metatarsophalangeal (MTP) dislocation of lesser toes.Methods:We retrospectively reviewed patients who underwent DMSS for chronic dislocation of MTP joints of lesser toes between January 2010 and December 2017 with follow-up of at least 24 months. Demographic data, radiographic measurements, functional outcomes, and complications were analyzed. Furthermore, the results of patients with short segment of shortening (group I, Results:Union was observed in 42 metatarsals (97.7%). Mean American Orthopaedic Foot & Ankle Society scale scores improved significantly from 42.2 (range, 15-65) preoperatively to 79.1 (range, 52-90) ( P < .001). Mean visual analog scale pain score improved significantly from 5.0 (range, 1-9) preoperatively to 1.8 (range, 0-6) ( P < .001). Complications included 1 nonunion, 1 osteonecrosis, 3 metatarsal angulation, 4 recurrent instability, 4 symptomatic osteoarthritis, 3 transfer metatarsalgia, and 1 floating toe. Group I included 23 MTP joints and group II included 20 MTP joints. There was no significant difference in clinical outcomes and complications between the 2 groups.Conclusion:DMSS was a reliable procedure for the treatment of chronic irreducible dislocated MTP joint of lesser toes. It provided satisfactory surgical outcomes and a low rate of postoperative complications, regardless of length of metatarsal shortening.Level of Evidence:Level III, retrospective comparative study.

Photoetching of n-type silicon induces a photoluminescent (PL) layer containing nanocrystals on the irradiated surface, usually through band gap absorption (wavelength

PURPOSE To evaluate the surgical outcome in terms of radiographic measurements, functional outcomes, and complications following arthroscopic ankle arthrodesis (AAA) in patients 60 years of age or older, and to compare the results of patients with mildly deformed ankle with those of patients with severely deformed ankle. METHODS We retrospectively reviewed patients who underwent AAA with 3 cannulated screws between January 2008 and December 2017 and followed postoperatively for at least 24 months. All included patients were 60 years of age or older. Demographic data and radiographic and functional outcomes were compared between patients with coronal deformity of less than 15° (group I) and those with a deformity equal to or greater than 15 degrees (group II). RESULTS A total of 41 patients with a mean age of 70.6 years were included (group I, n = 26; group II, n = 15) and mean follow-up was 51.4 months. Group II had significantly more severe preoperative coronal deformity of tibiotalar angle than group I (20.1 ± 2.9 vs 6.6 ± 4.1°, P < .01). Near-normal tibiotalar alignment was achieved postoperatively in both groups (group I, 3.4 ± 3.3 vs group II, 4.7 ± 3.1°, P = .227). Union was achieved in 39 (95.1%) patients with 2 cases in group I experiencing non-union. Union rate, mean American Orthopaedic Foot and Ankle Society ankle-hindfoot scale, and visual analog scale pain scores were not significantly different between the 2 groups at final follow-up. CONCLUSIONS AAA is a reliable procedure for end-stage ankle arthritis in patients 60 years of age or older resulting in a high union rate, encouraging radiographic and functional outcomes, and a low complication rate, even in cases with severe preoperative deformity. In addition, arthroscopic intra-articular malleolar osteotomy was a useful technique for correcting severe coronal deformity in our series. LEVEL OF EVIDENCE Level III, retrospective comparative study.

Background The aim of this study was to compare the radiographic and functional results between fixation and non-fixation in the Cotton osteotomy for the treatment of adult acquired flatfoot. Methods A retrospective, case-controlled study of consecutive stage IIB posterior tibial tendon dysfunction (PTTD) patients treated with the same bony reconstructive surgery including cotton osteotomy between 2013 and 2017. Meary’s angle, the medial arch sag angle (MASA), and medial cuneiform cobb angle (MCCA) were evaluated pre-operation, at first weight bearing after surgery, and 12 months post operation. Results Forty feet were included in the study. The cotton osteotomy utilized screw fixation (n = 20) or non-fixation technique (n = 20). No significant differences between groups were found in pre-operative and follow-up radiographic parameters, union rate, and functional results. Conclusion The non-fixation with press fit technique is a reliable procedure for Cotton osteotomy and as effective as screw fixation. Level of evidence Level III, case control study

Background: The deltoid ligament (DL) is an important stabilizer of the ankle. DL injury of varying severity can occur alone or with syndesmotic injury and fibular fracture. Limited diagnostic tools are available to assess DL injury quantitatively. Purpose: To establish an arthroscopic quantitative assessment of DL injury and to compare its performance with that of external rotation stress (ERS) and gravity stress (GS) radiography. Study Design: Controlled laboratory study. Methods: In total, 24 cadaveric lower extremities were divided into 4 groups: group 1 consisted of intact DL, group 2 of superficial DL disruption, group 3 of deep DL disruption, and group 4 of complete DL (superficial and deep) disruption. All specimens underwent sequential sectioning of syndesmotic ligaments, and medial clear space (MCS) was measured with ankle arthroscopy, ERS radiography, and GS radiography at different stages of syndesmotic sectioning. Results: For noninjured deltoid (group 1) and injured deltoid (groups 2-4), area under the receiver operating characteristic curve (AUC) of measurement of MCS was 0.939 for arthroscopy, 0.932 for ERS radiography, and 0.874 for GS radiography, with a significant difference between arthroscopy and GS radiography ( P = .014). For incomplete deltoid injury (groups 1-3) and complete deltoid injury (group 4), the AUC of MCS was 0.811 for arthroscopy, 0.656 for ERS radiography, and 0.721 for GS radiography, with a significant difference between arthroscopy and ERS radiography ( P < .001) and between arthroscopy and GS radiography ( P = .035). For all stages of syndesmotic sectioning, cutoff values of arthroscopic MCS with intact fibula were ≤2.5 mm for intact DL, between 2.5 and 3.5 mm for partial DL injury (superficial or deep), and ≥3.5 mm for complete DL injury. Arthroscopy was unable to detect a difference between superficial deltoid injury (group 2) and deep deltoid injury (group 3) in partial DL injury, with a measured MCS between 2.5 and 3.5 mm. The intraclass correlation coefficient of interrater reliability was 0.975 for arthroscopy, 0.917 for ERS radiography, and 0.811 for GS radiography. Conclusion: Arthroscopic MCS measurement can differentiate intact DL, partial DL injury, and complete DL injury. Compared with ERS and GS radiography, arthroscopic MCS measurement has greater accuracy with excellent interrater reliability. Clinical Relevance: For patients with suspected DL injury, arthroscopic MCS is useful for determining deltoid lesion severity based on defined cutoff values for consideration in preoperative planning to improve surgical outcomes.

The SARS-CoV-2 pandemic has had a significant impact worldwide. Currently, the most common detection methods for the virus are polymerase chain reaction (PCR) and lateral flow tests. PCR takes more than an hour to obtain the results and lateral flow tests have difficulty with detecting the virus at low concentrations. In this study, 60 clinical human saliva samples, which included 30 positive and 30 negative samples confirmed with RT-PCR, were screened for COVID-19 using disposable glucose biosensor strips and a reusable printed circuit board. The disposable strips were gold plated and functionalized to immobilize antibodies on the gold film. After functionalization, the strips were connected to the gate electrode of a metal-oxide-semiconductor field-effect transistor on the printed circuit board to amplify the test signals. A synchronous double-pulsed bias voltage was applied to the drain of the transistor and strips. The resulting change in drain waveforms was converted to digital readings. The RT-PCR-confirmed saliva samples were tested again using quantitative PCR (RT-qPCR) to determine cycling threshold (Ct) values. Ct values up to 45 refer to the number of amplification cycles needed to detect the presence of the virus. These PCR results were compared with digital readings from the sensor to better evaluate the sensor technology. The results indicate that the samples with a range of Ct values from 17.8 to 35 can be differentiated, which highlights the increased sensitivity of this sensor technology. This research exhibits the potential of this biosensor technology to be further developed into a cost-effective, point-of-care, and portable rapid detection method for SARS-CoV-2.

NiO/Ga2O3 heterojunction rectifiers were exposed to 1 Mrad fluences of Co-60 γ-rays either with or without reverse biases. While there is a small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000× reduction in forward current and a 100× increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on–off ratio is also reduced by almost five orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of −1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current–voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate that these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

The characteristics of sputtered NiO for use in pn heterojunctions with Ga2O3 were investigated as a function of sputtering parameters and postdeposition annealing temperature. The oxygen/ nickel and Ni2O3/NiO ratios, as well as the bandgap and resistivity, increased as a function of O2/Ar gas flow ratio. For example, the bandgap increased from 3.7 to 3.9 eV and the resistivity increased from 0.1 to 2.9 Ω cm for the O2/Ar ratio increasing from 1/30 to 1/3. By sharp contrast, the bandgap and Ni2O3/NiO ratio decreased monotonically with postdeposition annealing temperatures up to 600 °C, but the density of films increased due to a higher fraction of NiO being present. Hydrogen is readily incorporated into NiO during exposure to plasmas, as delineated by secondary ion mass spectrometry measurements on deuterated films. The band alignments of NiO films were type II-staggered gaps with both α- and β-Ga2O3. The breakdown voltage of NiO/β-Ga2O3 heterojunction rectifiers was also a strong function of the O2/Ar flow ratio during deposition, with values of 1350 V for 1/3 and 830 V for 1/30.

This study investigated a SARS-CoV-2 virus detection mechanism using dry-stored disposable strips. The accuracy of this sensing platform is as good as polymerase chain reaction (PCR) with a detection time of fewer than 30 s. SARS-CoV-2 antibodies were biofunctionalized on disposable strips similar to glucose detection strips to detect the presence and concentrations of SARS-CoV-2 in saliva samples. Eight 1 ms electric pulses were sent through the sensor strip with a saliva sample in its microfluidic chamber. A circuit board embedded with MOSFET was also employed to amplify the detected signals and convert the signal to digital readings displayed on an LCD screen. The COV-antibody functionalized disposable strips were stored in a dry condition for at least one day before analyzing clinical human saliva samples with known cycling threshold (Ct) values confirmed with conventional PCR tests. Results demonstrate our system is capable of showing qualitative positive or negative results within 30 s and providing quantitative SARS-CoV-2 concentrations in terms of Ct values in 5 min.

The temperature-dependent behavior of on/off ratio and reverse recovery time in vertical heterojunction p-NiO/β n-Ga2O/n+ Ga2O3 rectifiers was investigated over the temperature range of 25–300 °C. The device characteristics in forward bias showed evidence of multiple current transport mechanisms and were found to be dependent on the applied bias voltages and temperatures. The on–off ratio decreased from 3 × 106 at 25 °C to 2.5 × 104 at 300 °C for switching to 100 V reverse bias. For 200 μm diameter rectifiers, the reverse recovery time of ∼21 ns was independent of temperature, with the Irr monotonically increasing from 15.1 mA at 25 °C to 25.6 mA at 250 °C and dropping at 300 °C. The dI/dt increased from 4.2 to 4.6 A/ μs over this temperature range. The turn-on voltage decreased from 2.9 V at 25 °C to 1.7 V at 300 °C. The temperature coefficient of breakdown voltage was negative and does not support the presence of avalanche breakdown in NiO/β-Ga2O3 rectifiers. The energy loss during switching from 100 V was in the range 23–31 μJ over the temperature range investigated.

There is increasing interest in the alpha polytype of Ga2O3 because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga2O3 remains type II, staggered gap for annealing temperatures up to 600 °C, showing that this is a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga2O3. The magnitude of both the conduction and valence band offsets increases with temperature up to 500 °C, but then is stable to 600 °C. For the as-deposited NiO/α-Ga2O3 heterojunction, ΔEV = −2.8 and ΔEC = 1.6 eV, while after 600 °C annealing the corresponding values are ΔEV = −4.4 and ΔEC = 3.02 eV. These values are 1−2 eV larger than for the NiO/β-Ga2O3 heterojunction.

Biomimetic micro- and nanotechnology have substantially grown in recent years, contributing to significant progress in the pharmaceutical and biomedical domains [...]

BCl3 is an attractive plasma etchant for oxides because it is a Lewis acid used to scavenge native oxides on many semiconductors due to the strong B–O bonding. We investigated BCl3-based dry etching of the NiO/Ga2O3 heterojunction system. BCl3/Ar Inductively Coupled Plasmas produced maximum etch rates for NiO up to 300 Å.min−1 and 800 Å.min−1 for β-Ga2O3 under moderate plasma power conditions suitable for low damage pattern transfer. The selectivity for NiO: Ga2O3 was 2O3 had a stronger chemical component, without a well-defined ion energy threshold. The as-etched NiO and Ga2O3 surfaces show chlorine residues, which can be removed on both materials by the standard 1NH4OH: 10H2O or 1HCl: 10H2O rinses used for native oxide removal. According to the location of the Cl 2p3/2 peak, the Cl is ionically bonded.

A SARS-CoV-2 rapid detection technology employed commercially available test strips similar to the blood glucose test strips were developed with a detection time of 30 sec and the sensitivity as good as polymerase chain reaction (PCR). The analytical specificity of this technology was also investigated by testing the cross-reactivity and microbial interference on this biosensor platform using FDA suggested 31 different contaminants. Variants of SARS-CoV-2 have mutated along with the worldwide spread of the pandemic. Currently, the most common detection methods are PCR and lateral flow tests. The former takes more than an hour to obtain results and the latter has difficulty detecting the virus at low concentrations (for cycling threshold values, CT values, >25 to 27). Therefore, the demand for a fast, cost-effective, and low detection limit testing method has been significantly increased. In this work, 60 human saliva samples with 30 positive and 30 negative were collected and tested with PCR for SARS-CoV-2 prior to using our disposable strips. For this technology, the test strip was connected to the gate electrode of the MOSFET on the printed circuit board that serves to amplify signals. A synchronous double-pulsed bias voltages (around 1 ms) were sent to both the drain and gate of the MOSFET. The resulting change in drain waveforms was converted to digital readings and compared with cycling threshold (Ct) values of human samples to assess this sensor technology. The result signifies that positive human samples with a range of Ct values from 17.8 to 40 can be differentiated, along with proving none of those high-risk organisms would hinder the sensitivity of our system. Which demonstrated the potential of this system to be developed into a cost-effective and point-of-care rapid detection for SARS-CoV-2. Figure 1

In this study, we present a double-layer NiO/β-Ga2O3 p-n heterojunction diode, which exhibits high performance with breakdown voltage, on-resistance and turn-on voltage. β-Ga2O3 has been attracting great attention as one of the excellent materials for next-generation high-performance electronics, owing to its high Baliga’s figure-of-merit (BFOM), carrier mobility, critical breakdown field strength and low-cost, simple growth methods. β-Ga2O3 based unipolar devices, especially Schottky barrier diodes, have been developed rapidly; however, the lack of p-type doping in Ga2O3 remains a challenge for bipolar devices, which can more generally be utilized in practical applications. One of the possible strategies is to introduce a p-type material to construct p-n junctions with n-type β-Ga2O3. The NiO turns out to be a feasible p-type material that has a wide bandgap, adjustable doping concentration, intrinsic p-type conductivity and diverse deposition techniques to form a uniform film, such as sputtering, PLD and thermal oxidation. In this study, we fabricated the diodes from depositing Ti/Au for the back Ohmic contact metal and annealing at 550℃ in N2, followed by sputtering two NiO layers with different doping concentrations by tuning the ratio of Ar/O2. The Ni/Au contact metal was deposited onto the NiO layer after annealing at 300℃ under O2 ambient. Compared to typical NiO thicknesses of 300 to 500 nm, we turned to another trend with ultra-thin layers of NiO. The top layer NiO thickness is 10nm while the bottom layer of NiO thickness varies from 10 to 80 nm. Through the design of the ultra-thin (20 nm) double-layer NiO structure, the breakdown voltage (Vb) is substantially improved to 4.7 kV and demonstrates the on-resistance (Ron) of 11.3 mΩ·cm2, which leads to a figure-of-merit (Vb 2/Ron) of 2 GW/cm2. The high Vb is attributed to the structure of both the double-layer and the guard-ring designs. From the TCAD simulation, the peak of the electric field locates at the edge of the diodes. Increasing the doping concentration of NiO layer contact with Ni/Au can reduce the electric field on the edge of the Ohmic contact. On the other hand, the low doping concentration of the NiO contact with β-Ga2O3 can effectively move the electric field crowding on the edge to the inside of devices. In addition, the extension guard ring can also spread the electric field crowding. This work provides a desirable design strategy for p-n heterojunction, which has the highest breakdown voltage among all Ga2O3-based p-n diodes. Figure 1