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Fluoronitrile (C4F7N) has many advantages, such as high dielectric strength, low global warming potential (GWP), and short atmospheric lifetime compared to sulfur hexafluoride (SF6). C4F7N is mixed with carbon dioxide (CO2) to prevent liquefaction at the operating pressure of high-voltage power equipment. Therefore, it is essential to investigate the dielectric characteristics of the C4F7N/CO2 mixture gas for the development of environmentally friendly power equipment. The dielectric characteristics of C4F7N/CO2 at lower pressures have been previously reported. However, research into the breakdown characteristics of C4F7N/CO2 under high pressure environments is insufficient. Furthermore, the effect of oxygen (O2) content contributing to suppression of carbon soot formation by arc on breakdown characteristics of C4F7N/CO2 has rarely been investigated. Therefore, in this paper, the breakdown characteristics of C4F7N/CO2 according to the mixing ratio and O2 content were investigated while considering a high–pressure environment. The electrode arrangements were determined based on the field utilization factor in order to consider two types of electric field distribution. Alternating current (AC) and negative lightning impulse (-LI) breakdown tests were performed. From these experiments, under an extremely non-uniform electric field, it was confirmed that the dielectric strength of C4F7N 5%/CO2 95% at high pressure was about 75% of the strength of SF6. In a weakly non-uniform electric field, increasing the C4F7N content contributed to the improvement of dielectric strength by 31-77% relative to pure CO2 at the high pressure. Furthermore, it was investigated that the presence of O2 had no significant influence on improving the insulation performance.

Vertical extrinsic photoconductive semiconductor switches (PCSSs) are presented with initial characteristics comparison between V-doped 4H-SiC and Fe-doped GaN PCSS under axial triggering such as dark resistance, photoconductivity, power output, and breakdown behavior. Experiments are carried out under the 532-nm-wavelength laser with mJ-level energy and a pulse width of 30 ns. Photoconductive experiments show that the photoelectric conversion efficiency of GaN PCSS is 2.27 times higher than 4H-SiC PCSS with the same electric field strength under different laser energies from 1 mJ to 5 mJ. 4H-SiC PCSS with a dark-state resistance of $10^{12} \Omega \cdot $ cm can withstand a bias voltage of 8 kV (16 kV/mm) and laser energy of 8 mJ and the maximum output power is up to 428.7 kW, while that of GaN can only stand a bias voltage of 1 kV (2.9 kV/mm) because of low dark resistance and defect. Obvious cracks of 4H-SiC PCSS can be observed from the breakdown image after breakdown occurs, while the dark-state resistance of GaN PCSS drops from $10^{6} \Omega \cdot $ cm to $10^{4} \Omega \cdot $ cm under high DC voltage.

In this paper, a transfer learning technique was first utilized to obtain deep neural network models for different gate lengths in the avalanche breakdown regime. Once the characteristics of a gate-length metal-oxide-semiconductor field-effect transistor are measured and the data are used to obtain a deep neural network, behavioral models for different gate lengths are established by fewer hidden layers and less measured data at the desired biases and frequencies. Therefore, the training data through this method is significantly reduced and the accuracy of the testing dataset is comparable to that of the conventional artificial neural network technique. The predicted, measured, and simulated results based on the transit time theory at different bias voltages and frequencies are in good agreement. Multibias S-parameter behavioral models in the breakdown regime can be efficiently built using this technique. This approach can even be applied to other advanced technology nodes and can shorten the model building time for CMOS circuit design operating in the saturation and avalanche breakdown regions.

The electrical breakdown of synthetic air under ultrashort high-voltage pulses (50 ns duration), as well as slowly increasing (“DC”) voltages, is experimentally studied in a well-defined quasi-uniform electrode configuration (sphere–plane). The electrode spacing is varied from 0.1 to 1 mm, and the gas pressure is varied from 1.5 to 8 bar. The study’s goal is to provide experimental data to develop breakdown models that predict the breakdown probability of small gas gaps under arbitrary voltage excitations. In particular, this analysis is intended for applications where statistical and formative time lags need to be considered, such as nanosecond pulsed ignition or partial discharges in inverter-fed motors. The influence of the electrode material and the presence of UV illumination are investigated for both DC and pulsed voltages. The results highlight the important role of seed electron provision for breakdown under short transient voltages. Evidence for a field-assisted emission of seed electrons with a pressure-dependent onset field is found from time lag measurements. An empirical expression is derived based on the Fowler–Nordheim formula to quantify the seed electron generation rate. The expected dependence of the breakdown threshold on the cathode material (work function) was confirmed for breakdown under slowly increasing voltages (Townsend mechanism). Interestingly, a dependence of the breakdown voltage was also found for nanosecond pulsed voltages (dominated by the streamer mechanism). This suggests that the field emission of electrons from the cathode is the dominant source of seed electrons in large cathode electric fields.

Suppression pre-breakdown in planar separated absorption, grading, charge and multiplication (SAGCM) avalanche photodiodes (APDs) with the help of Floating Guard Ring (FGR) is still a research hotspot. In this paper, a lattice-matched InP/InGaAs-based SAGCM structure is grown by Metal-Organic Chemical Vapor Deposition and thus the planar 50 μm photosensitive area APDs with different FGR structures are fabricated using zinc diffusion process. The effects of the different lengths of FGR (4 μm, 8 μm, 12 μm, 16 μm), and the different distances between FGR and the Zn diffused p+ region (4 μm, 6 μm, 8 μm, 10 μm) on the optoelectrical characteristics are deeply studied. The results from optical microscope, scanning electron microscope and current-voltage curves reveal that there is an optimal length and distance for the punch-through and breakdown voltage. Furthermore, the nA-level dark current, gain (M) of up to 10 at breakdown voltage, responsibility as high as 9.01 A/W at M = 10 and quantum efficiency equaling to 72% are also tested and calculated, proving the good performance of our devices. The optimized FGR parameters and related structure are expected to be helpful for obtaining high-performance, small-size InP/InGaAs-based APDs.

A GaN Reverse-Conducting HEMT (RC-HEMT) is proposed and fabricated on the GaN/AlGaN/GaN platform. It features an integrated Schottky barrier diode (SBD) to realize reverse conduction and the double-heterojunction to enhance breakdown voltage (BV). Compared with the inherent reverse conduction capability of the conventional HEMT (Con. HEMT), the built-in SBD exhibits a low reverse turn-on voltage ( $V_{\text{RT}}$ ) and its $V_{\text{RT}}$ is independent of the threshold voltage and gate bias. At the off-state, the fixed positive and negative polarization charges form the polarization superjunction (PSJ). Therefore, the depletion region is extended and more uniform E-field distribution is obtained. Experimental results show that the RC-PSJ-HEMT achieves a low $V_{\text{RT}}$ of 0.68 V, which decreases 69.1% compared with that of the Con. HEMT. The BV of the RC-PSJ-HEMT (with $7.5 \mu \text{m}$ $V_{\text{GD}}$ ) is increased to 723 V from 202 V of the Con. HEMT.

In this letter, fin-shape tri-gate $\beta $ -Ga2O3 lateral MESFETs are demonstrated with a high power figure of merit (PFOM) of 0.95 GW/cm2 – a record high for any $\beta $ -Ga2O3 transistor to date. A low-temperature un-doped buffer-channel stack design is developed which demonstrates record high Hall and drift electron mobilities in doped $\beta $ -Ga2O3 channels allowing for low ON resistances (RON) in $\beta $ -Ga2O3 MESFETs. Fin-widths (Wfin) were 1.2- $1.5~\mu \text{m}$ and there were 25 fins (Nfin) per device with a trench depth of $\sim ~1~\mu \text{m}$. A $\beta $ -Ga2O3 MESFET with a source-drain length of 6.4 $\mu \text{m}$ exhibits a high ON current (187 mA/mm), low RON ($20.5~\Omega $.mm) and a high average breakdown field (4.2 MV/cm). All devices show very low reverse leakage until catastrophic breakdown for breakdown voltages (VBR) scaling from 1.1kV to ~3kV. This work demonstrates the potential of channel engineering in improving $\beta $ -Ga2O3 device performance towards lower conduction losses for low-to-medium voltage applications. [ABSTRACT FROM AUTHOR]

Vertical power devices require significant attention to their edge termination designs to obtain higher breakdown voltages without substantial increase in ON-state resistance. A simple edge termination structure for a GaN p-n diode is proposed, comprising a full layer lightly doped p-type GaN region underneath the higher doped ${p} +\!+$ contact layer. A TCAD model of the device is developed, and removal of the portions of ${p}$ ++ cap outside of the device active area in simulations is shown to increase the device blocking voltage capability. It causes the depletion width to increase in the lightly doped p-type layer and allows it to act similar to a junction termination extension (JTE). These predictions are validated empirically, resulting in a 52% measured increase in breakdown capability after selective removal of the ${p}$ ++ cap. This simple edge termination technique can be formed with only a single low-energy nitrogen implant or etching procedure, greatly increasing its manufacturability over more complex structures. Design optimization studies are pursued in TCAD to determine optimal parameter values for further improving breakdown performance. It is shown that the proposed edge termination technique can be employed to produce future high voltage vertical GaN devices without a significant gain in ON-state resistance and with wide tolerance to process variations. [ABSTRACT FROM AUTHOR]

By postulating that the electrical tree growth rate ($\textit {dl} / \textit {dt}$) is proportional to the rate of destruction due to partial discharges (PDs), a mathematical model for conductive electrical tree growth in dielectrics is put forward. Three types of solutions are presented for this mathematical model, which predict three cases of electrical tree growth in dielectrics; namely, the development case, the stagnation case, and the transition case. The physical nature of the three cases is presented, which is the comparison of the local field (${E}_{\text {loc}}$) and the critical field (${E}_{c}$) caused by the space charges due to a PD. When ${E}_{\text {loc}} > {E}_{c}$ , $\textit {dl}/\textit {dt} > {0}$ and the electrical tree develops. When ${E}_{\text {loc}} < {E}_{c}$ , $\textit {dl}/\textit {dt} < {0}$ and the electrical tree stagnates. When ${E}_{\text {loc}} = {E}_{c}$ , $\textit {dl}/\textit {dt} = {0}$ and the electrical tree stays at a transition state. [ABSTRACT FROM AUTHOR]

Heterostructure engineering in III-V vertical nanowire (VNW) MOSFETs enables tuning of transconductance and breakdown voltage. In this work, an InxGa $_{{1}-{x}}$ As channel with a Ga-composition grading (${x} \,\,=$ 1–0.4) in the channel and drain region, combined with field plate engineering, enables breakdown voltage above 2.5 V, while maintaining transconductance of about 1 mS/ $\mu \text{m}$ , in VNW MOSFETs. The field plate consists of a vertically integrated SiO2 layer and a gate contact, which screens the electric field in the drain region, extending the device operating voltage. By scaling the field plate, a transconductance of 2 mS/ $\mu \text{m}$ , alongside the breakdown voltage of 1.5 V, is obtained, demonstrating the benefit of field engineering in the drain. The scalability of the field plate and the gate is measured, showing an ON-resistance increase by 23 $\Omega \cdot \mu \text{m}$ , and transconductance decrease by 5 $\mu \text{S}/\mu \text{m}$ , per nm field plate length. This behavior is captured in a new and modified virtual source model, where device transmission and drain resistance are altered to capture the field plate scaling effect. The modeling is applied to nanowire (NW) devices with field plate lengths ranging from 5 to 115 nm, capturing accurately essential device performance parameters. Finally, a modified band-to-band (BTB) tunneling approach is used to accurately describe the device behavior above 1.5 V. [ABSTRACT FROM AUTHOR]

The breakdown characteristics of C4F7N/CO2 mixtures under dc condition are investigated with a particle-in-cell method. The processes of elastic, excitation, ionization, and attachment collisions are all considered. The elastic cross section of electron scattering from C4F7N is modeled through quantum mechanical spherical complex optical potential formalism. Based on the cross-sectional data, the dielectric strength of pure C4F7N is studied. The threshold of breakdown is in good agreement with the experiment. Besides, the dielectric strength of C4F7N/CO2 mixtures is also obtained. The threshold of breakdown in 80% C4F7N and 20% CO2 is larger than that of pure C4F7N when the gas pressure is larger than 1300 torr. The results show that the energy loss of electrons is mainly caused by excitation collision with CO2 when the energy of electrons ${T}_{e}$ is smaller than 5.5 eV. When ${E}/{P}$ is small, the proportion of low-energy electrons is large and ${T}_{e}$ increases with the ratio of C4F7N. Therefore, the effective ionization rate first decreases and then increases as the ratio of C4F7N increases. [ABSTRACT FROM AUTHOR]

Increasing demands for mass storage and new paradigm computing ask for non-volatile memories that can meet reliability requirements. Hf0.5Zr0.5O2-based (HZO) memory has attracted growing attention due to its excellent CMOS compatibility. This letter investigated the time dependent dielectric breakdown (TDDB) of HZO ferroelectric under both forward and reverse stress conditions, which is relevant to the memory’s practical operation. The key similarities and the differences for both breakdown conditions have been identified and the underlying mechanism is explored. It is found that the pre-existing oxygen vacancies near the bottom electrode play the key role and all the observed phenomenon can be explained. Therefore, the precise control of these pre-existing oxygen vacancies can be critical for future TDDB improvement.

The influence of pulse rise rate and pulse duration for ignition purposes in engines is investigated. A constant volume cell is used to characterize the breakdown voltage under nanosecond pulsed voltages with automotive sparkplugs having electrode gaps ranging from 0.2 mm to 1 mm. Two pulse generators are used to compare pulses with durations of 10 ns and 50 ns. Different pulse amplitudes are used, and air gaps with breakdown voltages ranging from 4 kV to 15 kV are investigated. The cell is filled with synthetic air with densities gap distances products that are relevant for internal combustion engines. This study shows that the pulse shape and rise rate influence the breakdown voltage. Under pulsed discharge, the breakdown voltage is always above the static breakdown voltage. The probability of pulsed discharge breakdown increases as both the pulse amplitude and duration increases. Furthermore, the breakdown voltage value increases with increasing pulse rise rate. The delay time between reaching the static breakdown voltage and the actual breakdown voltage decreases with increasing overvoltage. The delay time is constituted by statistical and formative times. Both the statistical and formative times decrease with increasing overvoltage. For ignition purposes, the pulse rise rate should be as high as possible to deliver a larger energy input in the breakdown phase. Furthermore, for reduced electrode erosion, the pulse duration should be short (10-20 ns) to reduce the probability for a transition to an arc.

Breakdown mechanism in 0.25- ${\mu } \text{m}$ gate length AlGaN/GaN-on-SiC iron doped high electron mobility transistors (HEMTs) with background carbon is investigated through the drain current injection technique. The measurement results reveal that it can be divided into two distinct stages according to the gate voltage levels. The first stage of the measured drain injected breakdown is mainly due to the initiation of the punchthrough process under the gate, and the second stage of breakdown is associated with the potential barrier between the unintentionally doped (UID) GaN and the Fe doped p-type GaN buffer layer which also has a higher carbon density. The electroluminescence (EL) results suggest that the first stage shows uniform punchthrough current flow, but localized leakage current flow associated with a snapback breakdown mechanism replaces the uniform punchthrough current flow and dominates the second stage. A 2D-TCAD simulation has been implemented and shows the current paths under uniform flow conditions. [ABSTRACT FROM AUTHOR]

Investigation of lightning strikes to conductors ran through long spans of rigid steel conduit was performed. An overdamped-exponential current waveform with controlled peaks and rise rates was used to inject simulated lightning strikes. The impact of the length of wire, length of conduit, grounding location/s, and load type was investigated. Breakdown of 600 V, 12 AWG, THHN insulated wire (3.23 mm OD, 2 mm conductor diameter) was observed for voltages above 45 kV. The presence of resistive loads (between wire and ground) in excess of 20 $\Omega $ or current rise times in excess of 5 kA/ $\mu \text{s}$ were found to consistently produce breakdown between wire and conduit. Practical power circuit elements such as outlets and splices were found to breakdown at voltage levels much below the wire insulation failure threshold. [ABSTRACT FROM AUTHOR]

The dynamic self-heating (SH) degradation was investigated on a-InGaZnO (a-IGZO) thin-film transistors (TFTs) under constant drain bias and varied gate pulses. Besides the negative shift of threshold voltage (${V}_{{\mathrm {th}}}$), similar with that under DC SH stress, the asymmetric degradations near drain and source revealed the concomitant hot-carrier (HC) effect. The HC-induced local barrier near drain could compensate certain SH-induced ${V}_{{\mathrm {th}}}$ shift, while a drastic SH effect would in turn enhance the HC barrier to high enough to cause hard breakdown. For a-IGZO TFTs under dynamic SH stresses, the interactions between SH and HC effects dominate the degradation behaviors and can be sensitively tuned by the falling time of gate pulse, suggesting a feasible method of lessening the dynamic instability. [ABSTRACT FROM AUTHOR]

The very high switching speed of wide bandgap semiconductor devices enables higher switching frequencies at lower losses. However, it can also cause negative effects on the insulation material. For investigating the effect of steep voltage slopes on interwinding insulation systems, a gallium nitride based full-bridge converter with digitally adjustable voltage slopes is developed and presented within this article. [ABSTRACT FROM AUTHOR]

High-field magnets use epoxy resin as the insulation for superconducting coil terminals. Surface flashover on the interface between the gas and solid insulation will cause insulation failure. In this paper, effects of high magnetic field on surface partial discharge and surface flashover of the epoxy resin are investigated. Experimental results show that high magnetic field causes the decrease of relative permittivity and further changes the electric field distribution along the surface of epoxy resin. Surface partial discharge behavior is directed by both the decrease of surface electric field at the interface and the decrease of breakdown voltage of air gap in high magnetic field. Lorentz force begins to play a role during the extension of electron avalanche by changing the migration of charge carriers and weakening the equivalent effect of the normal electric field near the triple junction. Opposite trends are observed with the increase of magnetic flux density when the direction of Lorentz force is parallel or perpendicular to the surface of epoxy resin. [ABSTRACT FROM AUTHOR]

To improve the electron mobility of quantum well (QW) gallium nitride (GaN) high electron mobility transistors (HEMT), we investigated QW and conventional AlGaN/GaN heterostructures grown by metal organic vapor phase epitaxy. Using calculation and experimental results, we revealed that the primary reason for the reduced electron mobility of the QW GaN-HEMT is the increase in intrasubband scattering events because of excessive electron confinement, which is caused by a strong polarization electric field. A strained Al0.30Ga0.70N/Al0.86Ga0.14N buffer structure was applied to alleviate the electric field in the GaN channel while maintaining a strong electron confinement. It enables to increase the piezo polarization of Al0.30Ga0.70N and thus, reduces that of the GaN channel. Consequently, the electron mobility improved to 1420 cm2/Vs for the QW GaN-HEMT structure with the Al0.30Ga0.70N/Al0.86Ga0.14N buffer from 1100 cm2/Vs for the common QW GaN-HEMT structure. To the best of our knowledge, 1420 cm2/Vs at a two-dimensional electron gas density of $1.5\times 10^{{13}}$ cm−2 is the highest electron mobility in the QW double heterostructure. [ABSTRACT FROM AUTHOR]

We demonstrate over 3 kV gate-pad-connected field plated (GPFP) β-Ga2O3 lateral MESFETs with high lateral figures of merit (LFOM) using metalorganic vapor phase epitaxy (MOVPE) grown channel layers and regrown ohmic contact layers. Using an improved low-temperature MOVPE selective area epitaxy process, we show that a total contact resistance to the channel as low as 1.4 Ω.mm can be achieved. The GPFP design adopted here using plasma-enhanced chemical vapor deposited (PECVD) SiNx dielectric and SiNx/SiO2 wrap-around passivation exhibits up to ~14% improved RON, up to ~70% improved breakdown voltage (VBR = VDS-VGS) resulting in up to 3 × higher LFOM compared to the non-FP β-Ga2O3 lateral MESFETs. The VBR (~2.5 kV) and LFOM (355 MW/cm2) measured simultaneously in our GPFP β-Ga2O3 lateral MESFET (with LGD = 10 μm) is the highest value achieved in any depletion-mode β-Ga2O3 lateral device to date. [ABSTRACT FROM AUTHOR]

Sandwich-structured nanocomposites have the potential to improve the mechanical and electrical properties of materials simultaneously. Nanofibrillated cellulose (NFC) modified paper sheet (denominated as N) and softwood paper sheet (denominated as P) are used to prepare insulating paper. Different kinds of insulating paper with the structures of PPP, NNN, NPN and PNP are prepared. Tensile strength, DC conductivity, dielectric response, space charge and breakdown strength are measured. The activation energies of prepared materials are calculated through DC conductivity at 30, 50, 70, and 90 °C. The mechanism for sandwich structure regulating the mechanical and breakdown properties of insulating paper is discussed. Oil impregnated N/P/N paper has a remarkable improvement on tensile strength, conductivity, and DC breakdown strength, which provides a promising scheme to obtain the insulating paper with outstanding tensile and breakdown strength. [ABSTRACT FROM AUTHOR]

PMIA (Poly-m-phenylene isophthalamide) is an ideal substitute for traditional cellulose paper in oil-immersed paper insulating scenarios. This paper studies the partial discharge characteristics of oil-immersed laminated PMIA. According to the q−φ scatter diagram, discharge quantity and discharge phenomenon, the partial discharge process of PMIA is divided into 3 stages: creeping discharge, co-existence discharge and pre-breakdown. The micro-structure and chemical components of damaged PMIA are presented. The carbon trace, functional groups, carrier trap characteristics and residual insulation strength in different stages of partial discharge are studied. This paper provides a theoretical basis for the application of PMIA in electrical insulation. [ABSTRACT FROM AUTHOR]

The electric field uniformity imposes a significant effect on the breakdown mechanisms of dielectric liquids. In general, breakdown is dominated by streamer initiation under uniform field, while it is dominated by streamer propagation under non-uniform field. This paper presents a study on identifying and quantifying the transition field factor boundary, represented by the field enhancement factor ƒ, between the two dominating breakdown mechanisms. The methods for deducing the transition field factor boundary are introduced. The first method from our previous study was developed by measuring and processing both the streamer initiation and breakdown voltages. In this paper, a new method is developed by only processing the breakdown voltage data. Based on the breakdown results reproduced from the literature, the transition field factor boundaries are derived for the mineral oil under both positive and negative lightning impulses. It is found that the negative transition field factor boundary is lower than the positive one. A four-region model is proposed to describe the effect of impulse polarity on breakdown mechanisms of dielectric liquids and to interpret the transition of breakdown mechanisms with respect to the field uniformity. [ABSTRACT FROM AUTHOR]

Understanding the DC breakdown characteristics of polymeric insulators is essential for stable operation of high-capacity DC electrical equipment. To predict the breakdown characteristics of low-density polyethylene (LDPE), we propose a numerical methodology with a new critical index in which the internal current varying with temperature, thickness, and injection barrier height. To evaluate this current-based index, we applied the fully coupled bipolar charge transport (BCT) and molecular chain displacement (MCD) models to analyze the influence of each variable on breakdown phenomena. The results of this analysis revealed that the amount of space charge accumulation within the insulator has a maximum value at approximately 50 °C, which corresponds to the known morphological transition temperature of LDPE. The breakdown strength calculated using this numerical model was found to decrease with increasing temperature and thickness. Although injection barrier height at the electrode was found to be negatively correlated with breakdown strength, its effect was not as significant as that of the other variables. The breakdown strength values obtained using this numerical method were found to be in close agreement with values reported in the literature. Based on these results, we newly suggest the physical quantity to predict the breakdown strength, the current relaxation speed, which is the slope of the Boltzmann sigmoid function, as a positively correlated index. Finally, we determined that the breakdown phenomena are initiated when the amount of impact accumulated in the insulator changes discontinuously and analyzed the contribution of factors affecting the breakdown using the Pearson correlation coefficient and the Sobol sensitivity index.

It is well-known that the high-performance polymeric dielectric films used for high-voltage DC capacitors should have outstanding capabilities in terms of electrical and mechanical properties in order to face harsh operating conditions. Many factors limit the ability of these thin films to face different and growing stresses according to modern electrical requirements. Microstructure properties, additives, impurities, defects formed during manufacturing as well as applied stress types significantly affect the performance of dielectric films and their operational lifetime. This paper presents a comprehensive review of the factors which affect the ageing, degradation and breakdown of metallised polypropylene (PP) capacitors films. The effects of microstructure, surface morphological properties, mechanical properties and defects on the reliability of biaxially oriented polypropylene films (BOPP) are studied. In addition, the phenomena affecting dielectric performance and ageing mechanisms which are induced by electrical, thermal and electrothermal stresses are discussed.

The electrical tree initiation and propagation behaviors are a key issue for the polyethylene-based cable insulation. This paper focuses on the effect of crystalline morphology on electrical tree growth characteristics of high-density and low-density polyethylene (HDPE/LDPE) blend insulation. In this paper, the electrical tree growth characteristics of HDPE/LDPE blends with HDPE mass fractions of 0, 10, 15, 20 wt% are investigated under repetitive impulse voltage at 40, 60, 80 °C. It is found that with the rise of HDPE content from 0 to 15 wt%, the growth rate and accumulated damage of electrical tree decreases, with the morphology of electrical tree tending to bush tree. The increasing of voltage amplitude improves the energy of injected charge while the temperature rise leads to the relaxation of molecular chain, which both result in the promotion of collision ionization, thus increasing the density of electrical tree. Compared with branch tree, bush tree illustrates better inhibition of discharge tracks due to uniform electric field at the end of branches. The crystalline characteristics of HDPE/LDPE blends indicate that the crystallinity increases with the addition of HDPE, and the blend comprising 15 wt% HDPE in an LDPE matrix apparently reduces the average size of spherulites and improves the distribution of spherulites evenly. The upsurge of crystal-amorphous interface leads to the increase of deep trap energy level density and the decrease of carrier mobility. Carrier injection and migration at the interface between crystalline and amorphous regions are restrained, thus inhibiting the growth of electrical tree. It is concluded that the crystalline morphology modified by polymer blending has a significant effect on the electrical tree growth characteristics.

In high voltage direct current (HVDC) cable systems, study of electric field distortion created by space charge accumulation is very important for examining insulation performance. Therefore, in this paper the influence of space charge on short-time breakdown characteristics of cross-linked polyethylene (XLPE) are studied. Trap energy distribution is an important factor affecting space charge behavior in dielectrics. Dielectrics with various thicknesses exhibit different space charge phenomena due to various trap distribution characteristics, which regulate the injection, migration and accumulation processes of charges. Consequently, trap characteristics can affect many parameters, such as charge accumulation depth and injection barrier. XLPE with thickness less than 100 μm show lower density of deep traps which can accumulate homogeneous bulk charges as compared to thick XLPE with thickness greater than 100 μm. This phenomenon determines the internal field strength distortion rate which is 20% larger for thin XLPE and it is much higher than that for thick XLPE. The external factor which is considered for analysis is applied field strength and it shows a linear proportional affect on the electric field distortion. A quantitative relationship model between applied field strength and distortion field strength of XLPE with different thicknesses was established. Linear extrapolation was used to obtain the trend of applied, distortion, and actual field strengths at different XLPE thicknesses when breakdown occurred. When the thickness of XLPE is less than 100 μm, distortion field strengths is higher than 50kV/mm and increases with decreasing thickness, resulting in a significant effect on the breakdown phenomenon and breakdown strength increases with increasing thickness. And when the thickness of XLPE is greater than 100 μm, the distortion field strengths is less than 50 kV/mm which also confirms the volume effect on breakdown phenomenon and breakdown strength decreases with increasing thickness.

Maintaining high average fields between the gate and drain is imperative in achieving near theoretical performance in ultra-wide band gap semiconductors like $\beta $ -Ga2O3. In this letter we report on a field management strategy to reduce the peak electric field at the drain side corner of the gate by using a composite dielectric layer consisting of an extreme permittivity dielectric like BaTiO3 and a low- $\kappa $ dielectric like SiO2 overlapped over the gate electrode. Using this strategy in $\beta $ -(Al0.18Ga0.82)2O3/ Ga2O3 double heterojunction field effect transistor, we achieved a record average breakdown field of 5.5 MV/cm at a gate-drain spacing of $1.15~\mu \text{m}$ along with an improved power figure of merit of 408 MW/cm2. The reported works shows the effectiveness of integrating extreme dielectric materials with ultra-wide band gap semiconductors in significantly improving breakdown performance. [ABSTRACT FROM AUTHOR]

To suppress space charge accumulation and minimize the antioxidant migration, polyethylene (PE) grafted with reactive hindered amine antioxidant MC prepared by melt radical grafting is investigated in this work. Fourier transform infrared spectroscopy is used to investigate the grafting reaction, which shows that the antioxidant MC is successfully introduced onto PEe Space charge distribution, DC conductivity, DC breakdown strength and thermally stimulated current are measured and the electronic structure is calculated from first-principles. The results show that PE grafted with antioxidant MC can effectively suppress space charge accumulation, reduce DC electrical conductivity and enhance DC breakdown strength. The polar functional groups of antioxidant MC anchored on PE macromolecular chain form immobile deep traps at the grafted MC sites, which can capture space charges and scatter charge carriers to reduce the amount, mobility and energy of charge carriers. Seen from the oxidative induction time of the specimens before and after acetone extraction, the level of retention of the grafted antioxidant MC are significantly higher than those of conventional antioxidant 300 and antioxidant 4020, which indicates that PE grafted with antioxidant MC has excellent long-term thermal oxidation stability. [ABSTRACT FROM AUTHOR]

Lifetime and reliability in realistic operating conditions are important parameters for the application of thin-film piezoelectric microelectromechanical systems (piezoMEMS) based on lead zirconate titanate (PZT). Humidity can induce time-dependent dielectric breakdown at a higher rate compared to dry conditions, and significantly alter the dynamic behavior of piezoMEMS-devices. Here we assess the lifetime and reliability of PZT-based micromirrors with and without humidity barriers operated at 23°C in an ambient of 0 and 95 % relative humidity. The correlation of the dynamic response, as well as the ferroelectric, dielectric, and leakage properties, with degradation time was investigated. In humid conditions, the median time-to-failure was increased from ${2.7\times }{10}^{4}{[1.9\times }{10}^{4}{-4.0\times }{10}^{4}{]}$ s to ${1.1\times }{10}^{6}{[0.9\times }{10}^{6}{-1.5\times }{10}^{6}{]}$ s at 20 $\text{V}_{{\mathrm {AC}}}$ continuous unipolar actuation, by using a 40 nm thick Al2O3 humidity barrier. However, the initial maximum angular deflection, polarization, and dielectric permittivity decreased by about 6, 11, and 12 %, respectively, for Al2O3 capped devices. For both bare and encapsulated devices, the onset of electrothermal breakdown-events was the dominant cause of degradation. Severe distortions in the device’s dynamic behavior, together with failure from loss of angular deflection, preceded time-dependent dielectric breakdown in 95% relative humidity. Moreover, due to the film-substrate stress transfer sensitivity of thin-film devices, water-induced degradation affects the reliability of thin-film piezoMEMS differently than bulk piezoMEMS. [2020-0228] [ABSTRACT FROM AUTHOR]

In this paper, the electric field, space charge and temperature distributions across a double layered dielectric are investigated under DC voltage. The dissimilarity of material properties of different layers, the effect of electric field and temperature dependent conductivity are found to play critical role in the electro-thermal problem of multi-dielectrics. At the interface, Maxwell-Wagner polarization is incorporated for electric field and interfacial charge, while temperature is considered as a continuous function of space inside the material. The current continuity equation, thermal continuity equation and Poisson's equation are simultaneously solved using numerical methods in parallel-plane electrode geometry. The electric field distribution, temperature distribution, space charge distribution and thermal breakdown limits are obtained at various boundary temperatures for different thickness proportions of layers. [ABSTRACT FROM AUTHOR]

Metal particles and bubbles are two typical impurities in transformer oil that can cause partial discharge (PD) and even electric breakdown. The PD characteristics are closely related to the motions of these impurities in flowing transformer oil. In this paper, the motions of impurities were obtained by a camera and a simulation model at first. Then, we employed three methods, namely, antennas, a non-inductive resistor, and the method recommended by IEC 60270, to measure the PD signals simultaneously. The breakdown experiments of transformer oil containing the metal particles and bubbles were also performed. In terms of these, single PD waveforms, statistical characteristics, and breakdown voltage were obtained. The results showed that the metal particles could excite ultrahigh frequency (300 MHz-3 GHz) PD signals, whereas bubbles only excited signals in the very high-frequency band (30-300 MHz). Moreover, the PDs induced by the metal particles had a higher repetition rate and a smaller amplitude than the PDs induced by bubbles. In addition, the metal particles easily caused PD, whereas bubbles easily led to the breakdown. Possible reasons for different discharge characteristics between the two impurities were discussed on the basis of the motions of impurities and the distortions of electric field.

Natural ester is a good substitute for mineral oil. It has been successfully applied in power transformers, and its application scale will continue to increase. With the aging of oil-paper insulation in transformers, moisture and impurity particles will inevitably be generated. In this paper, dry and wet mineral oil and natural ester samples, as well as dry and wet cellulose particles, were prepared. The accumulation behavior of the cellulose particles and the conductivity current in mineral oil and natural ester under a non-uniform dc electrical field were compared by using eight combinations of dry or wet cellulose particles and dry or wet insulation oils. The results show that the speed of the cellulose particles and the growth of impurity bridges are faster in wet mineral oil and natural ester, especially when the cellulose particles are also wet. The increase of electrical field strength accelerates the appearance of this phenomenon. The cellulose particle bridging phenomenon in the mineral oil is more significant than that in the natural ester. Under the same dc voltage, the saturated conductivity current in every mineral oil sample decreases as the electrode distance increases; however, the opposite phenomenon is observed in the natural ester samples. Moreover, the oil moisture content increase has a more significant influence on the saturated current and the dc breakdown voltage than the particles' moisture content increase. For the same particle concentration level, the natural ester has a lower conductivity current and a larger dc breakdown voltage than the mineral oil. The natural ester presents better resistance to particle pollution and better insulation properties than the mineral oil.

This paper deals with the effects of conductive and insulating nanoparticles at various sizes and concentrations on the ac dielectric strength of natural ester oil, namely, MIDEL 1204. The investigated nanoparticles are conductive (Fe3O4) and two insulating (Al2O3 and SiO2). The measurements of breakdown voltages are achieved according to IEC 60156 standard. Experimental findings show that the investigated nanoparticles have not a significant influence on insulation performances of natural ester oil as it is the case with mineral oils and synthetic esters. The best improvement does not exceed 7%; it is obtained with Fe3O4 (50nm) at a concentration of 0.4 g/L and Al2O3 (13 nm) at a concentration of 0.05 g/L. In some cases, the addition of nanoparticles even reduces the dielectric strength of natural ester oil. Indeed, a decrease of 15% is observed with SiO2 at a concentration of 0.05 g/L. The statistical analysis of experimental results is performed using two probabilistic functions, namely, normal and Weibull laws. It is shown that the breakdown voltage values of the investigated nano-liquids generally obey the normal and Weibull distributions. In addition, the breakdown voltage with a risk of 1% and 50% probability is deduced.

The performance of ultra-wide bandgap semiconductors like β-Ga2O3 is critically dependent on achieving high average electric fields within the active region of the device. In this article, we show that dielectrics like BaTiO3 with extremely high dielectric constant can provide an efficient field management strategy by improving the uniformity of electric field profile within the gate–drain region of lateral field-effect transistors. Using this strategy, we achieved high average breakdown field of 1.5 and 4 MV/cm at gate–drain spacing (Lgd) of 6 and 0.5~μm, respectively in β-Ga2O3, at a high channel sheet charge density of 1.6 × 1013 cm−2. The high channel charge density along with the high breakdown field enabled a record power figure of merit (Vbr2/RON) of 376 MW/cm2 at a gate–drain spacing of 3~μm. [ABSTRACT FROM AUTHOR]

We present a systematic investigation of device optimization for laterally diffused metal-oxide-semiconductor (LDMOS) field-effect transistors in terms of subthreshold leakage current, breakdown voltage, and ON-resistance for low-voltage (<10 V) power applications. We simulate and optimize n-channel 5-V LDMOS devices in order to reach a target leakage current and breakdown voltage. Device simulations and optimizations are performed by running an optimization algorithm, implemented as a computer code, on top of a commercial drift-diffusion simulation package. We find that n-channel LDMOS devices can realize leakage currents smaller than 10−13A/μm while maintaining a breakdown voltage exceeding 10 V for channel lengths down to 10 nm. Interestingly, we find an optimal ON-resistance for a channel length of 40 nm, while for shorter channel lengths the ON-state resistance increases with decreasing channel length. The increasing resistance for shorter channels is caused by electron mobility degradation as a result of an increasing body doping, needed to limit the leakage current. The optimal channel length presents a limit to conventional scaling of LDMOS devices, commonly used in low-voltage power applications. [ABSTRACT FROM AUTHOR]

A new method based on the charge simulation technique is proposed for computing the electric field in a short uniform field gap with space charge and without space charge of avalanches growing in the gap. The self-space-charge field of the avalanche is evaluated to result in field enhancement ahead of the avalanche due to electrons at its head and behind the avalanche due to positive ions in its wake. Also, a criterion is proposed for calculating the breakdown voltage and time-to-breakdown when the primary avalanche crosses the gap. The criterion is based on self-recurrence of the avalanche by secondary processes, and the most dominant one is the photoemission at the cathode. The condition of transition of the primary avalanche to anode- and cathode-directed streamers is formulated where the avalanche is chocked by its self-space-charge field. The number of electrons starting avalanche chains forming the streamers is evaluated in the gas ahead and behind the primary avalanche by photoionization and at the cathode by photoemitted electrons. The present computed values of the breakdown voltage of air at different pressures and N2 at atmospheric pressure as well as the time-to-breakdown in air at atmospheric pressure agree satisfactory with those recorded experimentally. The computed temporal variation of the size of the primary avalanche as influenced by its self-space-charge field agrees with that reported in the literature at different $E/N$ values. The computed current waveforms of the primary avalanche and its successor chains agree reasonably with those measured and those calculated using a finite-element method. [ABSTRACT FROM AUTHOR]

With projected performance advantages over silicon and incumbent wide-bandgap compound semiconductors, gallium oxide (Ga2O3) has garnered worldwide attention as an ultrawide-bandgap semiconductor material suitable for high-voltage, high-temperature, and radiation-hard electronics. Thanks to recent breakthroughs in crystal growth and device processing technologies, the research and development of vertically oriented Ga2O3 power transistors has made rapid strides. In this article, we review the important engineering achievements and performance milestones of the two major types of vertical Ga2O3 transistors—current aperture vertical metal–oxide–semiconductor field-effect transistors (MOSFETs) and vertical fin-channel MOSFETs. Challenges underlying the unique processing approaches to these devices and their implications on device reliability are also discussed. [ABSTRACT FROM AUTHOR]

We demonstrate that the residual carbon concentration in the drift region can have a significant impact on the reverse leakage, breakdown voltage, and breakdown stability of GaN-on-GaN vertical diodes. Two generations (Gen1, Gen2) of polarization-doped p-n junctions with different C concentrations were compared, in terms of avalanche voltage, avalanche instability, and deep-level concentration. The original results collected within this paper show that: 1) both generations of devices can safely reach the avalanche regime; diodes with a lower residual CN have a higher reverse leakage and a lower avalanche voltage, due to an uneven distribution of the electric field; 2) the presence of residual carbon can lead to breakdown walkout, i.e. a recoverable increase in breakdown voltage under reverse-bias stress. Specifically, devices with higher C concentration show a fully-recoverable breakdown walkout, whereas the breakdown voltage is stable in devices with lower C concentration; and 3) steady-state photocapacitance measurements confirm the presence of CN in both generations, and are used to assess the relative difference in concentration between Gen1 and Gen2, even for levels below secondary ion mass spectroscopy (SIMS) sensitivity. The results described in this paper indicate the existence of a trade-off between breakdown voltage (increasing by improving compensation) and breakdown stability (improving by reducing CN concentration) and are of fundamental importance for the optimization of GaN power devices. [ABSTRACT FROM AUTHOR]

In this paper, a liquid circulation system is constructed whereby gas bubble dynamics and electrical signal evolution preceding the oil gap breakdown are registered in stationary and flowing transformer oil. Based on a number of repetitive tests, two types of breakdown are classified: one takes place after bubble growth and originates in the bubble or the mixture of liquid and gas when the applied voltage is in the negative half-cycle; the other follows streamers resulting from the protrusion of bubble tip in the positive half-cycle. For each type of breakdown, partial discharge (PD) pulse is captured preceding the breakdown. As the oil flow rate varies, bubble dynamics change but the characteristics of each breakdown remain. In addition, it is found that oil breakdown voltage is improved as the flow rate increases. In terms of PD occurrence and bubble growth, the role of gas bubble in oil breakdown initiation, as well as the effect of oil flow on breakdown, is discussed. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the physicochemical properties of rice oil, peanut oil, corn oil and Kraft paper immersed in these oils in the presence of antioxidants (butylated hydroxytoluene, tertiary butyl hydroquinone and Naugalube¯ 750). The experiments are performed on new and aged conditions. Ageing of oils is carried at 115 °C for 96 hours while Kraft paper is aged in oils at 130 °C for 164 hours. Both closed and open cup methods are used for ageing. The results show that ageing insignificantly affects the breakdown voltage, but markedly increases the acid number and the viscosity of the vegetable oils. The combination of tertiary butyl hydroquinone and either butylated hydroxytoluene or Naugalube¯ 750 slightly increases the breakdown voltage, but significantly raises the oxidation stability of the vegetable oils. This results in a reduction in the viscosity and the acid number of the vegetable oils. Moisture significantly affects the breakdown voltage of both vegetable and mineral oil. High moisture content results in low breakdown voltage. The results also show that ageing insignificantly affects the breakdown voltage, but markedly decreases the tensile strength of oil-impregnated paper. Although the presence of antioxidants does not increase the breakdown voltage of aged paper, these additives slow down the ageing process. This results in an increase in tensile strength of the paper. [ABSTRACT FROM AUTHOR]

In view of the contemporary scenario and importance of alternative liquid dielectrics, IEEE DEIS Technical Committee on Liquid Dielectrics laid emphasis on pre-breakdown phenomena of ester dielectric fluids. The present article reports the background knowledge on the breakdown theories and behavior of streamers in insulating oils. The major influencing properties of the streamers aroused in liquid insulating systems are discussed keeping in view of the ester based dielectric fluids. Importantly, modelling of streamers, testing approaches, and review of pre-breakdown phenomena in ester dielectric fluids has been presented. [ABSTRACT FROM AUTHOR]

A new method, which involves the addition of alkaline Al 2 O 3 (3 wt%) and activated clay (5 wt%) as adsorbents for homogeneous synthetic trimethylolpropane triesters (TME), is reported here to not only improve electrical properties but also to shed light on future volume production. The results show that the acid value and the dielectric loss of TME oil is successfully reduced and meets IEC 61099. The viscosity of TME approaches that of mineral oil (MO) for transformers. In addition, TME oil with antioxidants exhibits fairly good oxidation stability that is evidenced by a notably high oxidation onset temperature of 226°C, which is 39 K and 14 K higher than that of commercial natural ester oil (NEO) (187°C) and MO (212°C), respectively. Furthermore, compared with the AC breakdown voltage (V b) of NEO (65.3 kV) and MO (70.4 kV), the TME oil has a higher V b =73.2 kV. Besides, the positive lightning impulse (LI) V b and streamer behavior of TME at small gaps are comparable to those of MO and NEO. However, the negative LI V b of TME and NEO are significantly lower than that of MO owing to the combined field variation towards the plane electrode which will facilitate the propagation of the streamer. Therefore, additives without oxygen, fluorine and chlorine should be given priority when they are used to improve the properties of insulation oil. [ABSTRACT FROM AUTHOR]

The isolation behaviour of polyimide thin films has been studied. Properties such as DC conductivity and the threshold electrical fields were obtained through a steady state current measurement under an applied voltage across a metal-insulator-metal capacitor. An inverse relationship has been found between the curing temperature and threshold electric field that would be applied to the structure. The results correlate with high voltage endurance life-time curves for digital isolators processed at different temperatures. [ABSTRACT FROM AUTHOR]

This work studies the avalanche characteristics of the 1.2 kV vertical GaN p-n diodes with implanted edge termination, based on quasi-static current-voltage (I-V) sweeps and unclamped inductive switching (UIS) tests. The UIS tests reveal a ~1.7 kV avalanche breakdown voltage ($BV_{{\text {AVA}}}{)}$ , 51 A maximum avalanche current (${I}_{{\text {AVA}}}{)}$ , and 63 mJ maximum avalanche energy (${E}_{{\text {AVA}}}$). The ${I}_{{\text {AVA}}}$ and ${E}_{{\text {AVA}}}$ are the highest reported in high-voltage GaN power devices. A lower $BV_{{\text {AVA}}}$ is observed in the I-V curves and a trap mediated avalanche model is proposed to explain it. The $BV_{{\text {AVA}}}$ in I-V curves is believed to be induced by avalanche-assisted trap-filling in the edge termination region, while the $BV_{{\text {AVA}}}$ in the UIS test reflects the robust avalanche at the main p-n junction. These results provide important new insights on the avalanche breakdown in GaN devices and address some seemingly contrary observations of vertical GaN p-n diodes published recently. [ABSTRACT FROM AUTHOR]

Ion bombardment of electrodes in an electric vacuum device can induce high-voltage breakdown. In order to explain this phenomenon, we, for the first time, analyzed a typical model of protons impacting the electrode with the help of a particle-in-cell (PIC)-direct simulation Monte Carlo (DSMC) code. In this model, we considered both the secondary electron yield and the gas desorption from the electrode. The temporal and spatial distribution evolution of electrons, ions, and neutrals under different electrode conditions is presented. The critical value of local gas density to induce breakdown is 1025 m−3. According to the discussion of the formation of the electrons avalanche, the electron ionizing gas is the key component for affecting the formation of a breakdown, and the production of plasma sheath near the electrode greatly contributes to the electrons avalanche. [ABSTRACT FROM AUTHOR]

Vertical III-V heterostructure MOSFETs exhibit outstanding performance at reduced supply voltages. In this letter, we report on a novel process of extending high-speed device operation towards higher voltages. The device vertical geometry allows for engineering a field plate by covering the nanowire drain area with a 10-nm-thick SiO2 film. The film acts as a field moderator in the device drain region. Reference devices without a field plate exhibit a transconductance of 2.5 mS/ $\mu \text{m}$ , while devices with a 120-nm-long field plate show 1.5 mS/ $\mu \text{m}$ but a three times increase in breakdown voltage. Measurements show that the field-screening effect attributes to reduced band-to-band tunneling and impact ionization, thereby reducing the parasitic bipolar effect in the MOSFET channel as well. The devices show promise in applications in circuits and systems requiring large power-handling. [ABSTRACT FROM AUTHOR]

In this paper, we report on achieving the first high performance lateral $\beta $ -Ga2O3 Schottky barrier diode (SBD) on sapphire substrate via transferring $\beta $ -Ga2O3 nano-membrane channel from a low dislocation density bulk $\beta $ -Ga2O3 substrate. Non field-plated lateral SBDs with Schottky–Ohmic contact distance of 4, 6, 11, and $15 \mu$ m demonstrate a reverse breakdown voltage (BV) of 0.64, 0.85, 1.2, and 1.7 kV with on resistance ( $R_\text {on}$ ) of 47, 66, 91, and 190 $\omega \cdot $ mm, respectively. This lateral $R_{\text {on}, \text{sp}}$ ~ BV performance is comparable to that of vertical SBDs. Combining with 107 ~ 108 high temperature current on/off ratio, $\beta $ -Ga2O3 SBD shows its great promise for power rectifying once the $\beta $ -Ga2O3 drift layer epitaxial growth becomes more mature.

During the operation of power transformers, the insulating oil is actually in a moving state due to the effects of various cooling systems. Therefore, the investigation on insulation characters of moving transformer oil is necessary. In this paper, the influences of temperature on partial discharge (PD) and breakdown characteristics of moving transformer oil contaminated by metallic particles were experimentally studied at first. It was found that the PD magnitude and frequency first decreased and then became higher when the temperature increased from 40 °C to 80 °C, and a minimum point appeared between 70 °C and 80 °C. On the contrary, the dependence of breakdown voltage on temperature showed an opposite tendency. In order to explain the experimental results, a simulation model involving multiple forces was constructed to obtain the movement trajectory of particles. The increase of oil temperature leaded to the decrease of dynamic viscosity of transformer oil, so the forces acting on particles and their movement characters changed. As the temperature increased, the collision frequency between particles and electrodes first decreased and then became higher, and there was a minimum point between 70 °C and 80 °C. This changing tendency was in accordance with the dependence of PD parameters on the oil temperature. In terms of the above results, the effects of temperature on PD frequency and breakdown voltage were discussed.

This letter reports high performance GaN ${p}$ - ${n}$ junctions with regrown ${p}$ -GaN by metalorganic chemical vapor deposition (MOCVD) on dry-etched surfaces. The breakdown voltage reaches 1.27 kV and the differential on-resistance is 0.8 $\text{m}\Omega \cdot \text {cm}^{{2}}$. The effects of etching powers and surface treatments on the reverse leakage characteristics of the regrown ${p}$ - ${n}$ junctions have been investigated. It’s found that lowering the etching power and damage is very effective to reduce the leakage currents and increase the breakdown voltages. Further analysis reveals that the charge concentration at the regrowth interface plays a critical role in the performance of the regrown samples. To avoid sacrificing the etching rate by using only low power etching, a multiple-RF-power etching recipe was developed with gradually decreased etching power. This work has demonstrated a practical and viable method to realize high performance regrown p-n junctions for various advanced GaN power electronics. [ABSTRACT FROM AUTHOR]