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Selective area growth (SAG) of gallium nitride (GaN) on silicon (Si) wafers efficiently relaxes the tensile stress that is generated in the GaN layer, when the structure is cooled down to room temperature after the growth. Hence, SAG enables the growth of thicker layers that are capable of operating at higher voltages than those grown in 2D layers. In this study, two GaN layers are grown by SAG on 200 mm-diameter Si(111) wafers by metal organic vapor phase epitaxy for the fabrication of pseudo-vertical p–n diodes. During the growth, the SiH4 precursor flow for the first sample was double than that for the second one. The uniformity of the doping concentration of the layers is investigated by scanning spreading resistance microscopy and the p- and n-type doped regions are examined by scanning capacitance microscopy. A low net doping concentration of 1.4 × 1016 cm−3 is extracted from capacitance–voltage measurements and a destructive breakdown occurs at 700 V for a 90 μm-diameter pseudo-vertical p–n diode. These results show the high potential of the SAG of GaN on Si wafers for vertical power devices. [ABSTRACT FROM AUTHOR]

The current research investigates the potential advantages of optimally combining wide bandgap Al2O3 with high dielectric constant (high-κ) Ta2O5 for gate dielectric applications. Various compositions of 10 nm AlxTayO oxide films are grown on the Al0.3Ga0.7N/GaN heterostructure by co-sputtering Al and Ta metals, followed by thermal oxidation at 500 °C. The average root-mean-square roughness of the grown oxide films is ∼1.2–1.4 nm compared to 0.4 nm for as-deposited metal. X-ray photoelectron spectroscopy and transmission electron microscopyconfirm the formation and thickness of the grown oxide films. The bandgap (E g) of the oxide films calculated from O 1 s electron energy loss spectra show a linear increase from 4.85 eV for pure Ta2O5 to 6.4 eV for pure Al2O3. The dielectric constant (ε ox ) calculated from capacitance–voltage (C G − V G) measurements decreases linearly from 25.7 for Ta2O5 to 7.9 for Al2O3. The interface trap density (D it ) is estimated from the frequency dispersion of capacitance–voltage (C G − V G) characteristics. The DC and radio frequency (RF) characteristics of AlxTayO/Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) devices are measured and compared with the Schottky HEMT devices (without any gate oxide). Compared to Schottky HEMT devices, AlxTayO/Al0.3Ga0.7N/GaN HEMT devices show superior DC characteristics, which helps us achieve maximum RF output power. Furthermore, the OFF-state measurements show that the AlxTayO/Al0.3Ga0.7N/GaN HEMT devices can sustain higher source-to-drain voltages, from a minimum of 88 V on pure Ta2O5 metal-oxide-semiconductor (MOS)-HEMTs to a maximum of 138 V on pure Al2O3 MOS-HEMTs before the dielectric breakdown happens, compared to a 57 V breakdown voltage on Schottky HEMT devices. An oxide variation of AlxTayO, with Al composition ratio of 0.34, shows an exceptional ION/IOFF ratio of 4 × 1011, a gate leakage current of 8 × 10−12 A/mm, a near-ideal subthreshold slope of 63.8 mV/dec, and the unity current gain frequency ( f T) of 25.6 GHz. [ABSTRACT FROM AUTHOR]

For microscale gaps, DC breakdown voltage is described theoretically and through simulation by accounting for field emission generated electrons and the subsequent ionization of neutral gas and ion-induced secondary electron emission. Here, we extend DC microscale breakdown theory to AC. Particle-in-cell (PIC) simulations show that breakdown voltage V varies linearly with gap distance d independent of frequency and the ion-induced secondary electron coefficient γ S E for d ≲ 4 μ m , where field emission dominates breakdown over ionization and avalanche. For d ≳ 4 μ m and γ S E = 0 , DC breakdown voltage increases linearly with d; for γ S E = 0.05 , DC breakdown voltage decreases to a minimum before beginning to increase at larger gap distances. For AC fields with γ S E = 0.05 , V behaves similarly to the DC case with the decrease corresponding to secondary emission occurring at higher voltages and larger gap distances with increasing frequency. At 10 GHz and γ S E = 0.05 , V resembles that of the DC case with γ S E = 0 up to ∼8 μm, suggesting that increasing the frequency effectively changes the number of ions striking the electrodes and the resulting electrons released. Phase space plots showing electron and ion velocities as a function of position across the gap show that electrons and ions are increasingly trapped within the gap with increasing frequency, reducing the number of ions that can strike the cathode and the subsequent secondary emission. Incorporating the resulting effective secondary emission coefficient for AC microscale gaps yields a simple phenomenologically based modification of the DC microscale gas breakdown equation. [ABSTRACT FROM AUTHOR]

In recent years, interest in synthetic C4F7N as a gas insulator has been growing due to its unique insulation properties and low global warming potential. In spite of this, very few studies are devoted to the analysis of the electric breakdown of C4F7N and its mixtures with other dilutants such as CO2 and N2. In the present paper, we use a two-dimensional fluid model to analyze the electrical breakdown of the atmospheric pressure C4F7N/N2 mixture. We establish the influence of the C4F7N fraction in the mixture and the cathode voltage rise rate on the breakdown voltage. We find that the ratio between the electron attachment frequency and the voltage rise rate defines the streamer parameters. Namely, if the time scale of electron attachment to C4F7N is much faster than the voltage rise rate, the plasma electronegativity of the streamer body and of its head is extremely high, and it is difficult to define exactly the streamer head location. In the opposite case of the fast rise rates, the conventional streamers with sharp heads were obtained. [ABSTRACT FROM AUTHOR]

The failure of polymeric solid insulation under transient voltages is closely associated with space charge. In this study, DC and AC field dependent conduction characteristics of epoxy resin were investigated using the space charge limited current and high voltage broadband dielectric spectrum methods. The breakdown voltages (BDVs) were examined over a wide range of DC voltage ramp rates. The results reveal a threshold effect of AC conduction loss below 600 Hz with respect to the electric field. By analyzing charge migration laws, a mobility distribution was deduced, with an upper limit of 10 − 9 m 2 V − 1 s − 1 , which is much higher than the measured DC mobility of 10 − 14 m 2 V − 1 s − 1 . A multi-mobility bipolar charge transport model was proposed by introducing the obtained mobility distribution. Compared to the single-mobility model, high-mobility carriers induce larger unblocked space charge currents for high dv/dt voltages, leading to lower values of BDV, which is consistent with experiment results. As the voltage ramp rate decreases, both simulation and experiment demonstrate higher BDVs due to the field shielding effect of homocharges. [ABSTRACT FROM AUTHOR]

Hardness of thin films is a noteworthy property in the electronic and mechanical industry and is generally observed to be dependent on the degree of roughening facilitated from surface heights' surface spatial heterogeneity at the mesoscopic observation scale. Nonetheless, owing to enhanced scale fluctuations and higher-order central moments, conventional parameters provide limitations and errors in capturing the spatial heterogeneity of surfaces. Herein, we have utilized scale-independent fractal parameters to analyze the spatial heterogeneity of surface heights in Ti1−xSixN ternary hard films deposited with varying Si doping concentrations using sputtering technique. The fractal dimension, lacunarity coefficient, Moran index, surface entropy, Otsu's separability, and fractal succolarity were computed to provide an overarching understanding of the surface heights' spatial heterogeneity. Principal component analysis was employed on the data sets to identify the parameter(s) accounting for the maximum variance and accordingly, the structure–property relation between spatial heterogeneity of surface and hardness is analyzed and discussed in the context of the fractal dimension of surface heights. The results indicate the possibility of mesoscopic surface engineering and, consequently, tuning of hardness and modulus of elasticity in Ti1−xSixN hard films by mere changing of surface spatial heterogeneity facilitated by the fractal dimension of surface heights. [ABSTRACT FROM AUTHOR]

The gate reliability of p-GaN gate high electron mobility transistors (HEMTs) was investigated in this Letter. Compared with conventional p-GaN gate HEMT, the in situ SiN cap-layer on the p-GaN layer can lift up the energy band and form a metal–insulator–semiconductor structure. With the introduction of an in situ SiN cap-layer, the DC electrical characteristics and reliability have been significantly improved. The reverse gate leakage current is reduced by 3 orders of magnitude. The threshold voltage shifts from 1.67 to 3.25 V, the on-resistances increased from 8.7 to 9.9 Ω mm, and the gate breakdown voltage is improved from 10.2 to 16.3 V. After conducting time-dependent gate breakdown measurement and predicting lifetime with a 10-year failure rate of 63%, it is calculated that the maximum allowable gate voltage increased from 6.3 to 11.4 V. The 10-year gate voltage swing has improved from 4.63 to 8.15 V. In addition, the in situ SiN HEMT exhibits good stability under high temperatures and long-term stress tests. The experimental results demonstrate that the in situ SiN cap-layer offers significant advantages in gate reliability. [ABSTRACT FROM AUTHOR]

We report high-Al-composition (HAC) Al0.51Ga0.49N vertical power Schottky barrier diodes (SBDs) on sapphire substrates grown by metal organic chemical vapor deposition. The fabricated vertical HAC AlGaN-on-sapphire SBDs exhibit a low turn-on voltage of 1.31 V, a high on/off ratio of ∼107, a low ideality factor of 1.35, and a high breakdown voltage of 662 V. [ABSTRACT FROM AUTHOR]

In high-power switching applications such as electric grids, transportation, and industrial electronics, power devices are supposed to have kilo-voltage (kV) level blocking capability. In this work, 1200-V gallium nitride (GaN) lateral field-effect rectifiers (LFERs) are demonstrated. The GaN-on-sapphire epitaxial structure is adopted to prevent vertical breakdown. To address electric field crowding, a p-GaN/AlGaN/GaN junction termination extension (JTE) is embedded in the anode region of the LFER. Comparing to the conventional LFER (Conv-LFER) fabricated on the same wafer, the JTE-anode LFER (JTE-LFER) achieves an improved breakdown voltage (>2.5 kV) and a lower dynamic ON-resistance (RON). The proposed p-GaN/AlGaN/GaN JTE offers a semiconductor-based solution (contrasted to the dielectric-based solution, i.e., field plate) to mitigate the high electric field, which is highly desirable for wide bandgap semiconductor power devices as it enhances the dielectric reliability. [ABSTRACT FROM AUTHOR]

In this Letter, we present a p-GaN gate enhancement-mode GaN-on-Si high-electron mobility transistor fabricated using Mg-acceptor re-passivation realized through ammonia plasma treatment. The gate-to-source and gate-to-drain access regions of the device were treated with ammonia plasma using a plasma-enhanced chemical vapor deposition system, resulting in the formation of a high-resistivity GaN cap layer. The fabricated device has a high threshold voltage (VTH) of 2.0 V and a low gate reverse leakage current (IGR) of 10−11 A/mm. A breakdown voltage (BVOFF) of 670 V together with a specific on-resistance (Ron,sp) of 0.87 mΩ cm2 was obtained in a device with LGD = 6 μm. The measured dynamic on-resistance (Ron,d) at a quiescent drain voltage (Vds,q) of 600 V with a stress time of 10 and 120 s is 1.06 and 1.34 times of the static on-resistance (Ron,s), respectively. Good thermal stability of VTH and gate current IG were observed after a thermal stress at 175 °C for 100 h. The developed fabrication techniques exhibit a great potential to be applied into GaN power transistors. [ABSTRACT FROM AUTHOR]

In high-power switching applications such as electric grids, transportation, and industrial electronics, power devices are supposed to have kilo-voltage (kV) level blocking capability. In this work, 1200-V gallium nitride (GaN) lateral field-effect rectifiers (LFERs) are demonstrated. The GaN-on-sapphire epitaxial structure is adopted to prevent vertical breakdown. To address electric field crowding, a p-GaN/AlGaN/GaN junction termination extension (JTE) is embedded in the anode region of the LFER. Comparing to the conventional LFER (Conv-LFER) fabricated on the same wafer, the JTE-anode LFER (JTE-LFER) achieves an improved breakdown voltage (>2.5 kV) and a lower dynamic ON-resistance (RON). The proposed p-GaN/AlGaN/GaN JTE offers a semiconductor-based solution (contrasted to the dielectric-based solution, i.e., field plate) to mitigate the high electric field, which is highly desirable for wide bandgap semiconductor power devices as it enhances the dielectric reliability. [ABSTRACT FROM AUTHOR]

In this work, the effect of offset channel length (Loffset) and the dielectric layer thickness (d) on the InSnO/InGaZnO (ITO/IGZO) dual-active-layer (DAL) high-voltage thin-film transistors (HV-TFTs) is systematically investigated. The characteristics of the DAL HV-TFTs resemble that of GaN high electron mobility transistors, wherein the breakdown voltages (VBD) reach saturation at a certain Loffset, and the on-resistance (Ron) linearly increases with Loffset. The linear fitting of Ron vs Loffset indicates that d has a multifaceted impact on the performance of HV-TFTs. In addition to its theoretical role in transistor models, d also influences the channel doping concentration and sidewall deposition issues in practical devices. The DAL HV-TFT with a 30-nm Al2O3 gate dielectric achieves a remarkable VBD of 450 V, the highest figure of merit of 118.2 kW/cm2, and a positive threshold voltage of 3.65 V. Both experiments and simulations indicate that the breakdown occurs within the semiconductor channel, paving the way for further improvement of the performance. [ABSTRACT FROM AUTHOR]

This work investigated the single-event effects (SEE) of NiO/β-Ga2O3 heterojunction diodes (HJDs) irradiated by 1.86 GeV tantalum ions with linear energy transfer over 80 MeV cm2/mg. The HJDs exhibited radiation responses with the early single-event leakage current (SELC) degradation until the fatal single-event burnout (SEB) failure, which was far below their breakdown voltages. Meanwhile, the surface morphology revealed the SELC damage expressed as burnout of topside NiO and metal stacks, while the SEB damage was observed as a burned hole in the β-Ga2O3 epitaxial layer. According to technology computer aided design simulations, the thicker p-type region in HJDs could further alleviate the electric field crowding effect exacerbated by the heavy-ion strike because of the extension of charge distribution in the p-type region. The SEB threshold was raised to 250 V by thickening the NiO layer to 300 nm. As for the SELC degradation process along with the burnout of topside stacks in HJDs, we supposed the probable reason was the intolerance of NiO to the high electric field under the SEE. This paper analyzed the SEE mechanism in β-Ga2O3 diodes and paved the way for heavy-ion irradiation hardening. [ABSTRACT FROM AUTHOR]

I-line stepper is widely used in large scale device manufacturing with limited achievable critical dimension by itself. With the aid of the spacer sidewall, the critical dimension can be further shrunk down. Spacer sidewall aided process necessitates an additional deposition-etching process, which inevitably results in process related damage under the gate. This paper proposes an optimized spacer sidewall aided gate patterning procedure for 0.15 μm GaN High Electron Mobility Transistors (HEMTs) fabrication. The process is proved to be effective in improving device performance compared to conventional sidewall process by keeping first Si-rich SiN passivation layer integrity at the gate edge. Interface trap density (Dit) and mobility were extracted for both conventional sidewall process and the optimized one with different passivation layers at the gate edge, demonstrating a lower Dit and higher mobility using the optimized process with enhanced device performances, such as higher current, breakdown voltage, and stress state characteristics, compared to the conventional process, which is promising for mass production of 0.15 μm GaN HEMTs. [ABSTRACT FROM AUTHOR]

This study presents a β-Ga2O3 Schottky barrier diode (SBD) with a Mg current blocking layer (Mg-CBL) fabricated via the Mg-doped spin-on-glass (Mg-SOG) technique, affording a surface roughness damage-free thermal doping process. The proposed technique improves the breakdown voltage (BV) of the β-Ga2O3 SBD from 580 to 2200 V and marginally increases the specific on-resistance from 4.0 to 4.8 mΩ cm2, yielding a notable power figure of merit exceeding 1 GW/cm2. The Mg-CBL effectively captures the electrons and mitigates the electric field, leading to a significant increase in BV and slight decrease in the forward current loss. The temperature-dependent I–V curves reveal that the reverse saturation current decreases owing to the physical mechanism of the Mg-CBL structure. Moreover, the Gaussian distribution model is applied to correct the Schottky barrier inhomogeneity stemming from the Mg-CBL. The results illustrate the promising potential of the Mg-CBL fabricated via the Mg-SOG technique for yielding high-performance β-Ga2O3 SBDs. [ABSTRACT FROM AUTHOR]

The diketopyrrolopyrrole-based polymer (DPPT-TT) has been employed in organic power field effect transistors due to its exceptional off-state breakdown performance. The impact of organic semiconductor layer thickness on the breakdown performance has not been explored. In this study, we investigate the impact of DPPT-TT layer thickness on the breakdown voltage (BV) by fabricating organic field effect transistors (OFETs) with various DPPT-TT layer thicknesses. Our findings reveal that the devices' BV is a strong function of DPPT-TT layer thickness, and reducing the DPPT-TT layer thickness from 68 to 15 nm results in a decrease in BV from 291 to 86 V, attributed to the two-dimensional (2D) electric field crowding effect. An analytical model utilizing the 2D Poisson equation reveals an electric field at the DPPT-TT layer's surface. Thinner DPPT-TT layer exhibits larger electric field peak, leading to premature breakdown near the drain electrode. The relationship between breakdown electric field and DPPT-TT layer thickness was established by fitting the experimental data to the model, revealing an average BV error of only 8.8%. This phenomenon is validated to be ubiquitous in polymer based OFETs via DPPT-TT-based and P3HT-based devices. According to the proposed model, this 2D electric field crowding effect can be mitigated by adjusting the dielectric layer thickness (tD) and/or the dielectric material. [ABSTRACT FROM AUTHOR]

In this paper, a ∼2 nm in situ SiN cap layer on AlGaN barrier layer is grown, which is revealed to be crystalline using high-resolution cross-sectional transmission electron microscopy. Benefitting from superior interface quality of epitaxial crystalline SiN/AlGaN interface, the gate diodes with in situ SiN cap layer feature lower interface trap state density than that with GaN cap layer. By comparing the GaN high electron mobility transistors (HEMTs) with the conventional GaN cap layer, the GaN HEMTs with in situ SiN cap layer exhibit improved device performance, showing higher electron mobility, higher drain current, larger on/off current ratio, and higher transconductance. For breakdown characteristics, the devices with in situ crystalline SiN cap layer show prominent advantages over the GaN cap layer with a 30% breakdown voltage increase to 810 V. [ABSTRACT FROM AUTHOR]

The impact of heavy ion irradiation on the β-Ga2O3 p-n diode and its physical mechanism have been studied in this Letter. After the irradiation fluence of 1 × 108 cm−2, it is observed that the electrical performance of the device is significantly degraded. The forward current density (JF) is reduced by 49.4%, the reverse current density (JR) is increased by more than two orders of magnitude, and the breakdown voltage (VBR) is decreased by 30%. Based on the results of the deep-level transient spectroscopy measurement, it is concluded that acceptor-like traps generated with an energy level of EC-0.75 eV in the β-Ga2O3 drift layer dominate the JF degradation of the device, which are most likely related to Ga vacancies. These acceptor-like traps result in the reduction of change carrier concentration, which in turn leads to a decrease in JF. In addition, according to the conductive atomic force microscope measurements and theoretical calculation, it is clearly observed that the latent tracks induced by heavy ion irradiation can act as leakage paths, leading to a significant degradation of JR and VBR. [ABSTRACT FROM AUTHOR]

Determining the characteristics of thermal field emission-induced breakdown is essential for various electron emission devices, such as thermionic energy converters. In previous studies, several mathematical models were developed to determine the breakdown voltages driven by field emission under different conditions; however, complicated computations were required to solve the numerical equations. There is still no consensus on the breakdown criterion when the thermal field emission comes into play. In this work, a unified breakdown criterion for the thermal field emission-induced microdischarge is proposed based on the definition of the thermal field emission coefficient γ TFE (combined with the thermionic emission coefficient γ TE and field emission coefficient γ FE ) from the emission current. The breakdown voltages scaling with the cathode temperature and gap distance are quantified. Distinct regimes corresponding to different electron emissions and their transitions are examined with the cathode temperature and gap distance tuned across a range of values. The results from this study provide an evaluation of thermal field emission-induced breakdowns and the dominant electron emission mechanisms in distinct regimes can be straightforwardly determined from the present model. [ABSTRACT FROM AUTHOR]

In this work, the influence of the Fe and Fe/C co-doped buffer on the AlGaN/GaN HEMTs is systematically investigated and compared. Due to the pronounced Fe tail in the unintentionally doped layer of the Fe-doped buffer compared to the Fe/C co-doped buffer, and the utilization of a two-step C doping process in the Fe/C co-doped buffer, it results in effectively reducing leakage current and increasing breakdown voltage without sacrificing saturation current and peak transconductance. Meanwhile, the RF characteristics of the Fe/C co-doped buffer are also superior to the Fe-doped buffer. More importantly, Drain Transient Current measurements indicate that the current collapse in the Fe/C co-doped buffer is smaller than that in the Fe-doped buffer. Through simulation analysis, the reason was identified: In the near-channel region, the weaker Fe tail effect in Fe/C co-doped buffer leads to a lower acceptor trap ionization. When the concentration of C exceeds 1 × 1016 cm−3, the ionization of traps introduced by Fe is suppressed. Additionally, the two-step C impurity distribution in the Fe/C co-doped buffer design modulates the electric field and potential, reducing the effective range of the electric field and potential, thereby effectively reducing the trap effects. These results are highly meaningful for the design of high-power amplifier epitaxial structures. [ABSTRACT FROM AUTHOR]

It is only recently that the electric vehicle (EV) has evolved into a contemporary invention. There has been a rapid acceleration in the development of EVs in a number of nations in order to lessen their reliance on oil and their contribution to environmental pollution. In the tangible world, fully EVs do not release any carbon dioxide (CO2) emissions from their tailpipes, unlike any other conventional vehicles. This results in a 50%–70% CO2 reduction in air pollution per year. The achievement of electrification in transportation has led to a reduction in the weight and size of the vehicles as the need for internal combustion engines can be eliminated. Wide bandgap materials such as silicon carbide (SiC) and gallium nitride (GaN) offer advantages in the manufacturing of EVs. Beginning the late 2000s, the EV industry has begun to adopt GaN devices in their manufacturing processes. The semiconductor material GaN stands out as a material for power electronic systems in EVs owing to its high switching frequency, higher temperature limit, and high voltage breakdown. This review aims to provide a comprehensive overview of semiconductor GaN materials for EV applications, which could be useful to provide insights for researchers and scientists to accelerate their innovation for the improvement of EVs. This review begins with an introduction to EVs, followed by the anticipated demand for EVs. The application of GaN devices in EVs, compared to the traditional Si and SiC devices, which are the primary power devices in current EVs, is discussed. The recent advancement in GaN devices that are capable of being used in various components of a fully automated EV, such as the battery, energy storage system, auxiliary power unit, and motor drive, in addition to their use in different non-automotive vehicles such as electric aircraft, electric ships, electric railways, electric submarines, and heavy duty vehicles, is also discussed. Finally, the challenges posed by GaN devices and potential solutions to overcome these shortcomings have been addressed. [ABSTRACT FROM AUTHOR]

The use of the low work function (4.5 eV) tungsten (W) as a rectifying contact was studied to obtain low on-voltages in W/Ga2O3 Schottky rectifiers and NiO/Ga2O3 heterojunction rectifiers that were simultaneously fabricated on a single wafer. The devices were produced with varying proportions of relative areas and diameters, encompassing a spectrum from pure Schottky Barrier Diode (SBD) to pure Heterojunction Diode (HJD) configurations. The turn-on voltages with W contacts ranged from 0.22 V for pure Schottky rectifiers to 1.50 V for pure HJDs, compared to 0.66 and 1.77 V, respectively, for Ni/Au contacts. The reverse recovery times ranged from 31.2 to 33.5 ns for pure Schottky and heterojunction rectifiers. Switching energy losses for the SBD with W contacts were ∼20% of those for HJDs. The reverse breakdown voltages ranged from 600 V for SBDs to 2400 V for HJDs. These are the lowest reported turn-on voltage values for 600/1200 V-class Ga2O3 rectifiers that extend the range of applications of these devices down to the voltages of interest for electric vehicle charging applications. [ABSTRACT FROM AUTHOR]

A two-dimensional axisymmetric fluid model was established to investigate the dynamic behavior of pre-ionized pulsed-direct-current helium plasma jets at atmospheric pressure. Our simulation results show that, at a relatively low pre-ionization level, the electron number density is reduced and the streamer propagation is decelerated before the plasma jet is ejected from the tube, which is attributed to the inhibitory effect of a recombination process between the positive ions in the streamer and the seed electrons near the anode. As the pre-ionization reaches a relatively high level, the electron number density is larger than that without pre-ionization before the plasma jet is ejected from the tube, which originates from the promotion effect of decreased breakdown voltage. These two competing mechanisms jointly dominate the dynamic behavior of gas discharge in the presence of pre-ionization. After the plasma jet is ejected from the tube, the enhanced discharge power is responsible for the strengthened electric field in the streamer head, augmented total ionization rate, accelerated streamer propagation, and increased number density of electrons and active species, whatever the pre-ionization density is. With the increase in pre-ionization density, the plasma jet length, streamer propagation speed, discharge power, and discharge energy exhibit the initial increase and subsequent decrease variation trend. The optimal enhancement effect is obtained at the pre-ionization density of 6 × 1012 m−3, with the plasma jet lengthened by 28.4% and the energy deposition efficiency enhanced by 28.1%. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid physics-data driven model for electrohydrodynamic gas system (EHDGS) was developed by combining artificial neural network (ANN) with mechanism modeling method. ANN was used to correlate the relationship between the variables (electrode distance, diameter of grounding cylinder, applied voltage, electric field gradient, etc.) in a needle-cylinder EHDGS and the initial space charge density. The results showed that the ANN model of nine neurons can well predict the initial space charge density. The coefficient of determination (R2) reaches 0.9874, and the mean absolute error is as low as 0.0067. Subsequently, a hybrid mechanism model where the initial space charge density was predicted from the ANN model was constructed to simulate the needle-cylinder EHDGS. The experiment with the needle-cylinder EHDGS was carried out. The simulation results were in good agreement with the experimental data, demonstrating the reliability of the proposed hybrid model. The electric field distribution, space charge distribution, and flow field distribution behavior of the EHDGS were then analyzed in detail. The effects of key parameters on the flow characteristics of EHDGS were systematically studied, showing that higher voltage and shorter distance give higher flow rate up to 2.5 m/s. The diameter of the cylinder also significantly influences the breakdown voltage. Three dimensionless groups were defined and their effects on spatial charge density distribution were investigated. This study provides both insights and an efficient tool for the design and optimization of EHDGS. [ABSTRACT FROM AUTHOR]

Different factors such as gas composition inside the low voltage circuit breaker (LVCB) chamber and the residual plasma in the post-arc stage affect the breakdown process, which in turn affects the breaking capacity of LVCBs. In this paper, the effects of non-parallel electrode structure, gas temperature and pressure, electrode temperature, and gap distance on gap breakdown of hot electrode under high temperature gas conditions were studied, for which a particle-in-cell/Monte-Carlo collision simulation model has been established, which takes into account the effects of high-temperature gas components, cathode electron thermal emission, electron collision ionization and other effects, and simulation studies have been conducted. The simulation results show that the increase in gap gas temperature, the decrease in air pressure, and the increase in electrode temperature will lead to the gap breakdown more easily. With the increase in the gap length, the breakdown voltage increases, but the average electric field intensity required for breakdown decreases. In the non-parallel electrode structure, the breakdown occurs first at the position with the shortest gap distance, then the cathode sheath forms and extends along the electrode surface to other areas, and finally, the entire gap breaks down. [ABSTRACT FROM AUTHOR]

The reliability issues in silicon carbide (SiC)-based devices with gate dielectric formed through heat oxidation are significant factors limiting their application in power devices. Aluminum oxide (Al2O3) was chosen as a high-k material to form the gate oxide layer on top of a SiC substrate. Atomic layer deposition (ALD) was used to fabricate an Al2O3/4H-SiC heterostructure, and the quality of the ALD Al2O3 layer was examined by XPS and electrical experiments. The XPS analysis suggests that the created heterojunction is a type-I heterojunction with ΔEC = 1.89 eV and ΔEV = 1.83 eV. Metal-insulated semiconductor structures with upper and lower Al electrodes were prepared for investigating leakage current and breakdown voltage characteristics. The leakage current density and breakdown electric field of an MOS capacitor structure with an Al2O3/4H-SiC heterojunction are ∼10−10 A/cm2 and 9.3 MV/cm, respectively. The interfacial defect density (Dit) near the conduction band of the MOS capacitive structure with the SiC substrate is 1.44 × 1012 eV−1 cm−2, while the interface charge (Neff) of the oxide layer of this sample can also be controlled at a level of 1011 cm−2. The Al2O3/SiC structure fabricated in this work exhibits superior electrical performance compared to the heterostructure based on the Si substrate and other relevant heterostructures documented in previous studies. [ABSTRACT FROM AUTHOR]

The effects of Mn and As doping in β-FeSi2 have been studied by theoretical simulations and electrical characterizations by analyzing Hall parameters within the temperature range of 20–300 K using mobility and the dual band model. The Hall resistivity ρ of doped samples increases linearly from a negative to a positive magnetic field (B), demonstrating the normal Hall effect at room temperature. High temperature Hall concentration increases significantly with the gradual increase in both Mn and As doping due to more and more ionization of the deep donor level. High temperature activation energies of Mn doped β-FeSi2 are considerably greater than that of low temperature energies, which demonstrates clear evidence of the dual band model. From density functional theory calculations, the origin of the dual band model has been validated from the electronic structure of β-FeSi2. Both density of states and charge transfer to the system upon doping have been investigated through the density functional theory, which demonstrates the Mn and As doped systems to be p-type and n-type, respectively. Both Mn and As doped β-FeSi2 exhibit p-type and n-type conductivities for spin down and spin up channels, respectively, in the presence of an external magnetic field, which will encourage its applications in novel spintronic devices. In addition, a β-FeSi2 based homo-junction diode fabricated from the Mn and As doped β-FeSi2 exhibits a cut-in voltage of 0.82 V, a reverse breakdown voltage of −10 V, and an ideality factor of 3.87. Thus, doped β-FeSi2 will be very much useful for fabricating an efficient and cost-effective solar cell if fabricated physically. [ABSTRACT FROM AUTHOR]

We report new data on the temperature coefficient of the avalanche breakdown voltage (BV) in 4H-SiC devices. We compare avalanche in different device types (MOSFETs/Schottky diodes), different measurement types [ I d (V d) -sweeps and unclamped inductive switching stress], and avalanche directions (vertical and lateral) for a wide range of avalanche voltages. We fit the measured B V (T) -curves to the one-sided abrupt junction model and extract values for the temperature coefficients of impact ionization coefficients in their Chynoweth and Thornber forms for both holes and electrons. [ABSTRACT FROM AUTHOR]

We report an N2 based annealing treatment to passivate interface traps (Dit) in n- and p-type 4H-SiC. The process has the potential to replace the commonly used hazardous and expensive gas nitric oxide (NO). N2 postoxidation annealing reduces Dit in both the upper and lower halves of the 4H-SiC bandgap, with a greater impact at the valence band edge. N2 annealing at 1500 °C is observed to be more effective in passivating traps and positive fixed charges than NO annealing for p-type devices, whereas for n-type devices, the opposite is true. The breakdown voltages for these devices are found to be lower than that of NO annealed devices. X-ray photoelectron spectroscopy has been performed to estimate the nitrogen areal density at the interface. Dit is measured as a function of nitrogen areal densities in the near interfacial regions for the different processes. Theoretical analysis through density functional theory is consistent with the measured Dit profiles by showing the generation of additional states near the valence band edge due to increased nitrogen concentration. In addition to reporting the effect of N2 annealing on both n- and p-type 4H-SiC, this work correlates the nitrogen areal densities at the interface to the Dit and explains the difference in Dit characteristics with nitrogen areal density between n- and p-type interfaces. [ABSTRACT FROM AUTHOR]

In this work, two series of AlGaN/GaN/AlN high electron mobility transistor (HEMT) heterostructures have been grown by molecular beam epitaxy on AlN bulk substrates. The effects of reduction in the GaN channel thickness as well as the AlGaN barrier thickness and composition on structural and electrical properties of the heterostructures have been studied. The material analysis involved high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. In a first series of HEMT structures grown with an aluminum content of 30% in the AlGaN barrier, the channel downscaling results in a reduction in the GaN strain relaxation rate but at the expense of degradation in the mean crystal quality and in the electron mobility with a noticeable increase in the sheet resistance. An opposite trend is noticed for the three-terminal breakdown voltage of transistors, so that a trade-off is obtained for a 50 nm width GaN channel HEMT, which exhibits a sheet resistance of 1700 Ω/sq. with transistors demonstrating three-terminal breakdown voltage up to 1400 V for 40 μm gate to drain spacing with static on resistance Ron = 32 mΩ cm2. On the other hand, a second series of HEMT structures with high aluminum content AlGaN barriers and sub-10 nm GaN channels have been grown perfectly strained with high sheet carrier densities allowing to preserve sheet resistances in the range of 880–1050 Ω/sq. [ABSTRACT FROM AUTHOR]

In recent years, non-thermal plasma technology has emerged as one of the most promising candidates for decomposing CO 2. The fluid model, a powerful tool to investigate the plasma dynamics, is computationally costly in simulating complex CO 2 plasma with tens of particles and hundreds of reactions, especially driven by short pulsed voltages. In this paper, a deep neural network (DNN) is proposed to describe the discharge characteristics and plasma chemistry of CO 2 pulsed discharge at atmospheric pressure. The DNN is trained using the simulation data obtained from the fluid model and then continuously optimized by minimizing the loss function. The effectiveness and feasibility of the DNN are verified by comparing with the experimental measurement and the numerical simulation results. Compared to the time-consuming fluid simulations with tens of hours, the well-trained DNN typically requires only a few seconds to obtain the essential characteristics of CO 2 pulsed discharges with high accuracy, significantly improving the computational efficiency. The DNN prediction results show that increasing the pulse rise rate at a given voltage amplitude can effectively raise the discharge current and breakdown voltage, and the electric field in the sheath region also increases with the pulse rise rate. In addition, the density of the surface charge accumulated on the dielectric layer increases with the plateau duration, and then a strong induced electric field by the surface charges is established, which obviously improves the discharge current during the pulse fall phase. The predicted data also show that increasing the pulse rise rate and the plateau duration could effectively improve the density of product species, such as CO and O 2 , leading to an increase in CO 2 conversion. This study demonstrates that the DNN method is a reliable tool for obtaining the essential discharge characteristics of atmospheric CO 2 pulsed plasma and provides a promising avenue for future applications of DNN-based methods in non-thermal plasmas. [ABSTRACT FROM AUTHOR]

Thermal management has become more critical as semiconductor devices are miniaturized. In metal–oxide–semiconductor field-effect transistors, the problem is the reduction in electron mobility in the channel layer owing to the temperature rise caused by heat generation near the channel-drain region. Focusing on the mean free paths of phonons and electrons in Si, nanostructures of a few 10 nm may only hinder heat propagation without affecting electron transportation. Therefore, inserting nanostructures into the channel layer may prevent a temperature rise and maintain a higher electron mobility. To discuss the relationship between the spacing between the nanopillars (NPs) and the heat generation and carrier behavior of the Si-NP/SiGe composite film, samples with NP spacings of 13, 27, or 47 nm were prepared. We previously confirmed that the thermal conductivity of the Si-NP/SiGe composite film decreased as NP spacing narrowed. The NPs scattered phonon propagation and suppressed heat propagation. However, carrier transport properties such as electrical conductivity, carrier mobility, and carrier lifetime have never been discussed. The laser heterodyne photothermal displacement method was used to examine the effect of nanostructures on carrier mobility and carrier lifetime of Si-NP/SiGe composite films. We observed that the carrier lifetime became longer when the NP spacing was comparable to the electron mean-free path of approximately 27 nm. [ABSTRACT FROM AUTHOR]

This document is a collection of research papers on wide- and ultrawide-bandgap electronic semiconductor devices. It focuses on the progress and challenges in developing devices made from wide-bandgap materials like GaN, AlGaN, AlN, Ga2O3, BN, and diamond for power, rf, and photonic applications. The papers cover topics such as improving GaN power devices, exploring new wide bandgap materials, and investigating gate insulator properties. Additionally, there are papers on defect detection, new concepts for wide bandgap devices, and the growth and properties of different materials. The research provides valuable insights for researchers interested in using these materials in electronic devices. [Extracted from the article]

In this Letter, an enhancement mode (E-mode) β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET) with quasi-two-dimensional channel was reported, and the channel mobility of 147.5 cm2/(V·s) is achieved. Low damage etching technology and low Ohmic contact resistance technology are introduced. As a result, the E-mode transistor demonstrates a maximum drain to source current (ID) of 230.5 mA/mm, a peak transconductance (Gm) of 54.2 mS/mm, a current gain cut-off frequency (fT) of 18 GHz, and a power gain cut-off frequency (fMAX) of 42 GHz. Additionally, a positive threshold voltage (VT) of 1.65 V, a breakdown voltage (VBK) of 420 V, and a specific on-resistance (RON,SP) of 1.24 mΩ·cm2 are achieved. Moreover, a fMAX × VBK of 17.64 THz·V and a fT × VBK of 7.56 THz·V are found to be a close value so far to the theoretical limit of β-Ga2O3. This device leads to excellent radio frequency (RF) characteristics, which paved the way for future millimeter-wave RF power electronics applications with β-Ga2O3 MOSFET. [ABSTRACT FROM AUTHOR]

This Letter reports a highly scaled 90 nm gate length β-Ga2O3 (Ga2O3) T-gate MOSFET with a power gain cutoff frequency (fMAX) of 55 GHz. The 60 nm thin epitaxial Ga2O3 channel layer was grown by molecular beam epitaxy, while the highly doped (n++) source/drain regions were regrown using metal organic chemical vapor deposition. Maximum on current (IDS,MAX) of 160 mA/mm and trans-conductance (gm) around 36 mS/mm were measured at VDS = 10 V for LSD = 1.5 μ m device. Transconductance and on current are limited by high channel sheet resistance (Rsheet). Gate/drain breakdown voltage of 125 V was measured for LGD = 1.2 μ m. We extracted 27 GHz current gain cutoff frequency (fT) and 55 GHz fMAX for 20 V drain bias for unpassivated devices. While no current collapse was seen initially for both drain and gate lag measurements for 500 ns pulse, moderate current collapse was observed after DC, RF measurements caused by electrical stressing. We calculated a high fT. VBR product of 3.375 THz V, which is comparable to the state-of-the-art GaN HEMTs. This figure of merit suggests that Ga2O3 could be a potential candidate for X-band application. [ABSTRACT FROM AUTHOR]

Schottky barrier height (SBH) enhancement directly translates into increased breakdown voltage (VBR) of β-Ga2O3 Schottky barrier diodes (SBDs). In this work, ultra-thin (5, 10, and 15 Å) oxygen-rich AlOx interfacial layers (ILs), deposited using plasma-enhanced atomic layer deposition, are shown to enhance the SBH of post-metallization oxygen annealed Pt/AlOx/β-Ga2O3 SBDs by up to 0.8 eV resulting in a maximum VBR of nearly 500 V (2× gain) on 2–4 × 1016 cm−3 doped substrates, without compromising the specific on-resistance. The SBH and VBR enhancement is observed on ( 2 ¯ 01) as well as (001) surfaces. X-ray photoelectron spectroscopy (XPS) analysis shows that excess oxygen interstitial concentration in 5 Å AlOx films decreases (increases) with increasing thickness (oxygen anneal), making them more stoichiometric. The decreasing (increasing) trend in SBH and VBR with increasing IL thickness (oxygen anneal) is consistent with the XPS-derived O/Al ratio of the films and the formation of an AlOx/β-Ga2O3 interfacial dipole due to a difference in oxygen areal densities. The AlOx deposition can be easily integrated with field management methods such as field plates and guard rings that can further enhance β-Ga2O3 SBD performance. [ABSTRACT FROM AUTHOR]

The discharge arc of a high-current gas spark switch has a strong mechanical effect on the electrode and adjacent objects. The measurement of this mechanical effect on the electrode plays a very important role in switch design and the theoretical study of spark discharge. However, in traditional stress measurement systems, the spatial electromagnetic interference caused by the discharge and the high electrode voltage affects the measurement accuracy and can even damage the experimental instrument. In this paper, an electrode impact stress measurement system based on PVDF piezoelectric film is designed to measure the electrode stress under a strong spatial electromagnetic field and high voltage. The experimental results show that the system can measure the impact pressure of high-voltage and high-current gas spark switch electrodes. The starting time of the stress measurement waveform shows that the shock to the electrode is formed in the initial stage of current buildup. The measured results clearly show the high magnetic field force component in the electrode impact pressure waveform. The shock waveforms induced by different pulse capacitor values, breakdown voltages, and loads are examined. It is found that the shock stress waveforms applied to the electrodes are affected by the peak value of the current, dI/dt, and the discharge duration. [ABSTRACT FROM AUTHOR]

To satisfy the need for low jitter in gas switches at repetition rate and enhance insulation reliability during high voltage operation of the trigger, we propose a micro-jet triggering system. This system requires less energy and can use a laser power supply as an energy source. It effectively improves the insulation stability of the trigger when working at high potentials and achieves a good triggering effect with low jitter at low working coefficients. The breakdown characteristics were tested by double-pulse experiments. Ensuring the same operating conditions for both pulses, the pulse interval was varied to obtain the breakdown voltage dispersion at different repetition rates. The results indicate that the dispersion of the breakdown voltages can reach 0.16% at a frequency of 50 Hz with a pulse front of 30 μs, representing an order of magnitude reduction compared to the 1.45% at switching self-breakdown, and decreases further as the air pressure rises. In addition, the size of the microcapillary has an impact on the dispersion of breakdown voltage. It was found that for a range of lengths from 2 to 6 mm and aperture sizes from 80 to 400 μm, the trigger jitter was lower when the length was larger and the aperture was smaller. Furthermore, a trigger life test was performed on the ceramic capillary, and after one million triggers, the system remained stable with no degradation in trigger performance. [ABSTRACT FROM AUTHOR]

The C4F7N/CO2 mixed gas is most expected to replace SF6 in high-voltage power equipment, and the generation of free metal particles in gas-insulated equipment is unavoidable and highly susceptible to inducing insulation failures. In this paper, the effects of flaky, spherical, and mixed shape aluminum particle defects on the breakdown characteristics of C4F7N/CO2 mixed gas are investigated and compared to those of SF6 under the same conditions. The experimental results show that the effect of particle defects on the insulating properties of C4F7N/CO2 gas mixtures is visualized by the fact that particle defects reduce the breakdown voltage of C4F7N/CO2 gas mixtures, increase their stochasticity, and reduce the enhancement of the insulating properties of C4F7N/CO2 gas mixtures by increasing the air pressure. The greater the number of particles, the greater is the degree of influence. Comparison of the SF6 and C4F7N/CO2 gas mixtures reveals that, in the case of flake defects, increasing the air pressure improves the insulation performance of the SF6 gas better than that of the C4F7N/CO2 gas mixture. Under the condition of the same number of particles, the larger the proportion of spherical particles in the hybrid particles, the smaller is the influence of metal particles on the C4F7N/CO2 mixed gas and on SF6 gas. [ABSTRACT FROM AUTHOR]

High-k gate dielectrics have attracted a great deal of attention in the investigation of transistors due to their unique properties such as superior gate controllability. However, their integration into graphene field-effect transistors (GFETs) remains problematic and the physical mechanisms governing the performance of these devices are still not fully understood. In this study, the effects of post-annealing on GFETs utilizing the high-k HfLaO ternary oxide as the gate dielectric were comprehensively investigated. The HfLaO film was deposited on top of graphene by magnetron sputtering, and the device performance with various post-annealing temperatures was conducted. It was found that post-annealing temperature can effectively increase the dielectric constant through balancing the oxygen-vacancy defects and moisture absorption. Both the surface morphology of HfLaO and performance of GFETs were investigated, and the fabricated GFETs exhibit notable electrical performance enhancements. Specifically, GFETs with a 200 °C post-annealed HfLaO gate dielectric demonstrate the optimal device performance, featuring a minimal Dirac point voltage (VDirac) of 1.1 V and a minimal hysteresis (ΔVDirac) of 0.5 V. The extracted hole and electron mobilities are 4012 and 1366 cm2/V · s, respectively, nearly one order of magnitude higher than that of GFETs with as-deposited HfLaO. This work outperforms other existing GFETs utilizing high-k gate dielectric and chemical vapor deposition grown graphene in terms of both carrier mobility and on–off ratio. It is also noted that the excessive post-annealing temperature can negatively impact the GFET performance through introducing oxygen vacancies, increasing the surface roughness, lowering the breakdown voltage, and inducing recrystallization. [ABSTRACT FROM AUTHOR]

A fast-switching low-loss field-stop insulated gate bipolar transistor with a dual control gate (DIGBT) of a semi-insulating polycrytalline silicon (SIPOS) material is proposed in this paper. Because the SIPOS has uniform high resistance, it has an approximate linear electric potential distribution. When DIGBT conducts, the higher electric potential on SIPOS causes the P-type drift region (P-drift) to generate an inversion layer of electrons, adjusting the number of carriers and making the generation of non-equilibrium carriers no longer dependent on the doping concentration in P-drift (Nd) but on the electric potential distribution on SIPOS. Therefore, it can solve the contradiction among the breakdown voltage, forward voltage drop [VCE(sat)], turn-off time (toff), and turn-off loss (Eoff) caused by the Nd. Through Technology Computer Aided Design (TCAD) simulation, the VCE(sat) of DIGBT is 30.6% lower than that of SJFS IGBT. Meanwhile, DIGBT reduces the toff by 62.8% while reducing the Eoff by 83.0% compared to SJFS IGBT. In addition, the static latch-up I–V and the forward biased safe operating area of the DIGBT have been significantly improved. This paper adjusts the number of carriers through the characteristics of SIPOS material, enabling the above-mentioned physical phenomena to be applied in insulated gate bipolar transistor power devices and achieving device performance breakthroughs. [ABSTRACT FROM AUTHOR]

In this Letter, a Ga2O3 vertical Schottky barrier diode (SBD) with self-aligned field plate and mesa termination is fabricated and studied. The combination of field plate and mesa termination can effectively make the electric field distribution uniform in the termination, and thus the proposed SBD features high breakdown voltage (BV). Moreover, to eliminate alignment deviation and simplify the fabrication process, a self-aligned etching process is developed. The experimental results show that a low specific on-resistance of 4.405 mΩ·cm2 and a high BV of 3113 V can be simultaneously derived on the proposed SBD, yielding a high power figure of merit of 2.2 GW/cm2. Meanwhile, a considerably low forward voltage of 1.53 V at 100 A/cm2 is also achieved, demonstrating the low conduction loss of the device. [ABSTRACT FROM AUTHOR]

Transformer oil plays the role of heat dissipation and insulation in power transformers, and its electrical and thermal characteristics are directly related to the stable operation of the transformer. At the same time, it is important to master the electric–thermal characteristics of transformer oil for transformer state evaluation, latent fault prediction, and maintenance planning. Based on this, the gas production rule and electrical characteristics of transformer oil under accelerated aging are studied in this paper. First, the experimental platform for power transformer aging is established to accelerate the aging of power transformers. Second, the accelerated aging transformer oil is taken as the research object, and the power frequency, DC, lightning, and gas chromatography are measured and analyzed. Finally, a transformer oil aging evaluation model is established, which takes into account four factors: carbon and oxygen gas factors in transformers, life loss factors calculated by hotspot temperature, hydrocarbon gas factors dissolved in transformer oil, and oil quality factors, and conducts aging evaluation. The conclusion shows that the T parameter proposed in this paper can effectively evaluate the quality of transformer oil. When T is less than or equal to 0.6, there is no aging of the oil. When T is greater than 0.6 and less than 1, the transformer oil has been aging, but it is not manifested. Those are parameters whose chromatography and breakdown voltage are not far beyond the IEEE standard. When T = 1, the aging of oil with significant changes in gas content and breakdown voltage can be observed. When T is greater than 1, the oil has undergone serious aging. [ABSTRACT FROM AUTHOR]

In this study, the (001) β-Ga2O3 surface was dry etched employing the inductively coupled plasma-reactive ion etching (ICP-RIE) system, and Au/Ni/β-Ga2O3 Schottky barrier diodes (SBDs) were fabricated on the etched surface. The impact of ion bombardment on the (001) β-Ga2O3 surface during dry etching and its effect on current-voltage (I–V) characteristics and breakdown voltage was investigated. The forward current at higher bias decreased with increasing temperature due to the fact that the higher temperatures cause them to be less mobile owing to the scattering effects that reduce the on-current. The temperature-dependent I–V characterization of the Au/Ni/β-Ga2O3 SBD revealed a strong temperature dependence of barrier height and ideality factor associated with the barrier height inhomogeneity at the interface between Ni and β-Ga2O3. Analysis of the barrier height inhomogeneities with the assumption of Gaussian distribution of barrier heights confirmed the presence of a double Gaussian barrier distribution having mean barrier heights of 0.71 and 1.21 eV in the temperature range of (83–158) and (183–283 K), respectively. The Richardson constant value obtained from the modified Richardson plot interpreted with the consideration of Gaussian distribution of barrier heights closely matched with the theoretical value of β-Ga2O3. The fabricated Au/Ni/β-Ga2O3 SBD showed consistent breakdown voltage in the range of 670–695 V over repeated measurements with a time interval of 1 min without exhibiting any damage. However, after an initial breakdown voltage measurement, repeating the measurement with a 30 s interval led to an exponential increase in current, leading to the destruction of the device, associated with the low thermal conductivity of the substrate. The results obtained reveal that the ICP-RIE dry etching did not cause significant damage to the surface. [ABSTRACT FROM AUTHOR]

We report on the growth of Si-doped homoepitaxial β-Ga2O3 thin films on (010) Ga2O3 substrates via metal-organic chemical vapor deposition (MOCVD) utilizing triethylgallium (TEGa) and trimethylgallium (TMGa) precursors. The epitaxial growth achieved an impressive 9.5 μm thickness at 3 μm/h using TMGa, a significant advance in material growth for electronic device fabrication. This paper systematically studies the Schottky barrier diodes fabricated on the three MOCVD-grown films, each exhibiting variations in the epilayer thickness, doping levels, and growth rates. The diode from the 2 μm thick Ga2O3 epilayer with TEGa precursor demonstrates promising forward current densities, the lowest specific on-resistance, and the lowest ideality factor, endorsing TEGa's potential for MOCVD growth. Conversely, the diode from the 9.5 μm thick Ga2O3 layer with TMGa precursor exhibits excellent characteristics in terms of lowest leakage current, highest on-off ratio, and highest reverse breakdown voltage of −510 V without any electric field management, emphasizing TMGa's suitability for achieving high growth rates in Ga2O3 epilayers for vertical power electronic devices. [ABSTRACT FROM AUTHOR]

This Letter demonstrates a high-performance 3.3 kV-class β-Ga2O3 vertical heterojunction diode (HJD) along with an investigation into its off-state leakage mechanism. The vertical β-Ga2O3 HJD with field plate assisted deep mesa (FPDM) termination was fabricated using a self-aligned technique to etch the deep mesa to a depth of 9 μm, thereby reducing electric field crowding at the anode edge. In addition, a thick dielectric is deposited to fill the trench, facilitating the utilization of a field plate to further reduce the electric field at the anode edge. TCAD (Technology Computer Aided Design) simulations show significant suppression of electric field crowding at the anode edge. The fabricated HJD exhibits a high current swing of ∼1010 over a temperature range from 25 °C to 175 °C. The specific on-resistance (Ron,sp) is extracted to be 3.9 mΩ cm2, and the breakdown voltage is 3.42 kV with the FPDM termination. These conduction and blocking characteristics lead to a high power figure of merit of 3 GW/cm2, which is one of the highest among multi-kilovolt β-Ga2O3 diodes. Furthermore, the off-state current leakage mechanism of the HJD under a reverse bias up to 2000 V was investigated. The fitted results reveal that the leakage current is primarily dominated by Poole–Frenkel (PF) emission, with the trap level of PF extracted to be 0.36 eV below the conduction band of NiO. [ABSTRACT FROM AUTHOR]

In this work, high threshold voltage and breakdown voltage E-mode GaN HEMTs using an Al:HfOx-based charge trapping layer (CTL) are presented. The developed GaN HEMTs exhibit a wide threshold modulation range of ΔVTH ∼ 17.8 V, which enables the achievement of enhancement-mode (E-mode) operation after initialization process owing to the high charge storage capacity of the Al:HfOx layer. The E-mode GaN HEMTs exhibit a high positive VTH of 8.4 V, a high IDS,max of 466 mA/mm, a low RON of 10.49 Ω mm, and a high on/off ratio of ∼109. Moreover, the off-state breakdown voltage reaches up to 1100 V, which is primarily attributed to in situ O3 pretreatment effectively suppressing and blocking leakage current. Furthermore, thanks to the VTH of GaN HEMTs being tunable by initialization voltage using the proposed CTL scheme, we prove that the direct-coupled FET logic-integrated GaN inverters can operate under a variety of conditions (β = 10–40 and VDD = 3–15 V) with commendable output swing and noise margins. These results present a promising approach toward realizing the monolithic integration of GaN devices for power IC applications. [ABSTRACT FROM AUTHOR]

Power Schottky barrier diodes (SBDs) face an inherent trade-off between forward conduction loss and reverse blocking capability. This limitation becomes more severe for ultra-wide bandgap (UWBG) SBDs due to the large junction field. A high Schottky barrier is usually required to suppress the reverse leakage current at the price of an increased forward voltage drop (VF). This work demonstrates a Ga2O3 junction barrier Schottky (JBS) diode that employs the embedded p-type NiO grids to move the peak electric field away from the Schottky junction, thereby allowing for the use of an ultra-low barrier TiN Schottky contact. This JBS diode concurrently realizes a low VF of 0.91 V (at forward current of 100 A/cm2) and a high breakdown voltage over 1 kV, with the VF being the lowest in all the reported vertical UWBG power diodes. Based on the device characteristics measured up to 200 °C, we further analyze the power loss of this JBS diode across a wide range of operational duty cycles and temperatures, which is found to outperform the TiN/Ga2O3 SBDs or NiO/Ga2O3 PN diodes. These findings underscore the potential of low-barrier UWBG JBS diodes for high-frequency, high-temperature power electronics applications. [ABSTRACT FROM AUTHOR]

Diamond Schottky barrier diodes (SBDs) could theoretically operate at high voltage, high temperature, and high frequency and be potentially used in power electronics. However, the device breaks down prematurely and cannot operate stably at high voltages due to the edge electric field crowding. In this work, a vertical diamond SBD with a curved field plate (CFP) was prepared using a chemical reflow method, inductively coupled plasma etching, and electron-beam evaporation. This structure alleviates the electric field crowding at the edge of the Schottky electrode and results in a breakdown voltage and current density of 380 V and over 3000 A/cm2, respectively. After repetitive measurements, we found that the device can repeatedly breakdown at around 380 V. These results indicate that CFP structure diamond SBDs have great application in high-voltage and high-power electronic devices. [ABSTRACT FROM AUTHOR]