High Breakdown Voltage Research Articles

Design of Ga2O3 Trench Gate MOSFET Devices with Dielectric Pillars

Abstract In this study, a β-Ga2O3 U-groove gate metal-oxide-semiconductor field-effect transistor (UMOSFET) with a high breakdown voltage (BV) is proposed. Through TCAD simulation, both forward and reverse electrical characteristics are comprehensively investigated. The integration of traps within the current blocking layer (CBL) is suggested to enable effective current blocking. Furthermore, to optimize the BV, the introduction of oxide dielectric pillars on either side of the drift layer is implemented to enhance the potential distribution during breakdown. The forward and reverse electrical characteristics of the device at different temperatures are also investigated. Additionally, by conducting simulation optimizations of different doping concentrations in the drift layer, CBL layer thickness, and trap concentrations, notable achievements are realized, which include a high BV of 865.2 V, low threshold voltage of 2.587 V, and low specific ON-resistance of 19.2 mΩ·cm2. This study presents a novel structural design to foster the potential application and development of Ga2O3 electronic devices.

High breakdown voltages on pseudo-vertical p–n diodes by selective area growth of GaN on silicon

High breakdown voltages on pseudo-vertical p–n diodes by selective area growth of GaN on silicon

Plasma Treatment Technologies for GaN Electronics

Nowadays, the third-generation semiconductor led by GaN has brought great changes to the semiconductor industry. Utilizing its characteristics of a wide bandgap, high breakdown Electric field, and high electron mobility, GaN material is widely applied in areas such as 5G communication and electric vehicles to improve energy conservation and reduce emissions. However, with the progress in the development of GaN electronics, surface and interface defects have become a main problem that limits the further promotion of their performance and stability, increasing leakage current and causing degradation in breakdown voltage. Thus, to reduce the damage, Plasma treatment technologies are introduced in the fabrication process of GaN electronics. Up to now, designs like the high-resistivity p-GaN cap Layer, passivating termination, and surface recovery process have been established via Plasma treatment, reaching the goals of normally-off transistors, diodes with high breakdown voltage and high-reliability GaN electronics, etc. In this article, hydrogen, fluorine, oxygen, and nitrogen Plasma treatment technologies will be discussed, and their application in GaN electronics will be reviewed and compared.

Device structural engineering and modelling of emerging III-nitride/β-Ga2O3 nano-HEMT for high-power and THz electronics

Abstract III-nitrides, such as gallium nitride (GaN) and aluminium nitride (AlN), possess a wide bandgap, a high breakdown voltage, and a high thermal conductivity, making them an attractive choice for high frequency and high-power applications. A further benefit of III-nitride-based HEMTs is their high current density, low noise figure, and higher electron mobility, which enable efficient radio-frequency signal amplification. In this research work, the polarization induced graded buffer technique and improved lattice matched β-Ga2O3 substrate is employed to minimize the buffer-related issues in III-Nitride Nano-HEMTs (high electron mobility transistors), such as reduction in the buffer leakage current losses. The polarization-induced doping in buffer region can considerably reduce the buffer leakage current, enhance breakdown voltage and RF characteristics, and bend the conduction band upwardly convex, improving two-dimensional electron gas (2DEG) confinement. A detailed comparison between the graded buffer technique of the HEMT and the HEMT having normal buffer has been conducted. The results demonstrated that the suggested HEMT demonstrated better DC and RF characteristics up to the Tera (1012) hertz range of frequencies. The improved characteristics of the proposed HEMT allow it to be a feasible solution for emerging technologies and cutting-edge communication systems that require efficient signal processing at very high frequencies.

Insights of Physicochemical Structure Changes of Bituminous Coal with Acidification-assisted Controlled Electric Pulse through SEM, XRD and FTIR

Controlled electric pulse (CEP) cracking coal effectively enhances its permeability, but a high coal breakdown voltage (BV) can result in technical difficulties. To address this problem, the method of using HCl solution to improve the electrical conductivity of coal was proposed. The effects of HCl on coal BV were investigated, and the microstructural changes in coal were analyzed through scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Compared with raw coal, the BV of acidified coal decreased significantly. The crushing degree of the coal samples was clearly enhanced with an increasing HCl concentration. Some internal coal minerals were acidified and dissolved, the aromatic layer spacing (d002) increased and the layer sheet stacking height (Lc) decreased, and the crystal structure was damaged. When acidified coal was broken down, numerous internal pores and cracks appeared, active coal groups were shed, the aliphatic hydrocarbons and oxygen-containing functional group contents increased, surface activity was reduced, and the hydroxyl content was reduced, which was conducive to rapid gas desorption. Acidification effectively reduces the BV of coal and improves the cracking and permeability enhancement effect of coal by CEP action.

650 V vertical Al0.51Ga0.49N power Schottky diodes

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.

Thermal Conversion of Ultrathin Nickel Hydroxide for Wide Band Gap 2D Nickel Oxides.

Wide band gap (WBG) semiconductors (E g > 2.0 eV) are integral to the advancement of next-generation electronics, optoelectronics, and power industries owing to their capability for high-temperature operation, high breakdown voltage, and efficient light emission. Enhanced power efficiency and functional performance can be attained through miniaturization, specifically via the integration of device fabrication into a two-dimensional (2D) structure enabled by WBG 2D semiconductors. However, as an essential subgroup of WBG semiconductors, 2D transition metal oxides (TMOs) remain largely underexplored in terms of physical properties and applications in 2D optoelectronic devices, primarily due to the scarcity of sufficiently large 2D crystals. Thus, our goal is to develop synthesis pathways for 2D TMOs possessing large crystal domains (e.g., >10 μm), expanding the 2D TMO family and providing insights for future engineering of 2D TMOs. Here, we demonstrate the synthesis of WBG 2D nickel oxide (NiO) (E g > 2.7 eV) thermally converted from 2D nickel hydroxide (Ni(OH)2) with a lateral domain size larger than 10 μm. Moreover, the conversion process is investigated using various microscopic techniques, such as atomic force microscopy, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, providing significant insights into morphology and structural variations under different oxidative conditions. The electronic structure of the converted Ni x O y is further investigated using multiple soft X-ray spectroscopies, such as X-ray absorption and emission spectroscopies.

A 326 nm pure ultraviolet light sources achieved in a Ga[formula omitted]O[formula omitted] microwire heterojunction through interface optimization and surface-modification

Low-dimensional Ga2O3 single-crystals have caused widespread attentions in the potential of developing ultraviolet light sources due to its ultrabroad bandgap, low-budget, high thermally stable, high breakdown voltage and others. Herein, we exhibit a significant route to construct one-dimensional Ga2O3 microwire heterojunction deep-ultraviolet light-emitting diode (LED). The resulting electroluminescence is positioned at 326 nm with a narrow linewidth of about 22.5 nm, which is the shortest wavelengths once published for the Ga2O3-related light sources. In the well-fabricated LED, an intermediate AlN layer enables appropriately to manipulate band alignment of n-Ga2O3/p-GaN heterojunction, thus achieving efficient confinement of electron–holes spreading and radiative recombination within the Ga2O3 microwire active medium. Benefited from surface-modified Pt nanoparticles, the LED’s electroluminescence efficiency and brightness can be plasmonically boosted. More importantly, the peak energy at 3.8 eV obtained under forward bias, which is smaller than the Ga2O3 bandgap, could be resulted from radiative recombination of weakly-bounded electron–holes inside the Ga2O3 microwires. Therefore, the Ga2O3 monocrystalline wires synthesized using high-temperature carbothermal reduction, are expected as promising-looking candidates to develop environmentally friendly, easy miniaturization, highly-stable deep-ultraviolet light sources and photonic devices.

Demonstration of aluminum nitride metal oxide semiconductor field effect transistor on sapphire substrate

Abstract Aluminum nitride (AlN) is a promising ultrawide bandgap material with significant advantages for power electronics and optoelectronic applications due to its high breakdown voltage, mobility, and thermal conductivity. AlN Schottky barrier diodes (SBDs) and metal semiconductor field effect transistors (MESFETs) have shown potential but are limited by issues such as high off-state leakage current and complex structures to achieve ohmic contacts. To address these challenges, we report on the fabrication and characterization of an AlN metal oxide semiconductor field effect transistor (MOSFET) with a recessed gate structure. The source and drain contacts were fabricated on n-doped AlN epitaxy using Ti-based contacts with a Ti/Al/Ti/Au metal stack. To evaluate the performance of these contacts, a circular transmission line model (CTLM) was employed, and contacts were annealed at various temperatures ranging from 750 to 950 °C in a nitrogen ambient. Our results reveal that unannealed Ti-based contacts on AlN showed no current conduction. However, annealing these contacts at 950 °C for 30 s significantly reduced the specific contact resistance to 0.148 Ω·cm2, achieving an ~80% reduction compared to samples annealed at 750 °C. Utilizing these optimized contact conditions, we fabricated, to the best of our knowledge, the first AlN MOSFET. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, an effective mobility of 2.95 cm2/Vs, an on-off current ratio spanning two orders of magnitude, and a reverse breakdown voltage of approximately ~250 V in air without a field plate. 

Optimizing Forward Drop and Reverse Leakage Trade‐Off in AlGaN/GaN Lateral Diode with Schottky‐Metal‐Insulator‐Semiconductor Cascode Anode

Herein, AlGaN/GaN lateral diode with the Schottky‐Metal‐Insulator‐Semiconductor (MIS) cascode anode (CALD) to optimize forward voltage drop (VF) and reverse leakage current (ILEAK) trade‐off is proposed. In the CALD device, a normally‐on Ni/HfO2/AlGaN MIS‐controlled channel as well as a lateral Ni/GaN Schottky contact are cascoded at the anode. The designed normally‐on MIS‐controlled channel has high electron concentration at forward bias and prevents high electric‐field at reverse bias, which ensure both low VF and low ILEAK. Meanwhile, the Ni/GaN Schottky contact with a high Schottky barrier height further suppresses the ILEAK. As a result, the fabricated CALD demonstrates an optimized VF–ILEAK trade‐off relationship, including a low VF of 1.6 V and a low ILEAK of 5.2 × 10−8 A mm−1 (at reverse voltage of 400 V), together with a high breakdown voltage (BV) >700 V. These high performances suggest that the CALD can be a promising candidate for GaN power diode applications requiring a better VF–ILEAK trade‐off.

Evolution of ferroelectric and piezoelectric properties of BiFeO3 ceramics doped with lanthanum and zirconium

In this study, we performed cation substitutions at Bi-site (La3+) and Fe-site (Zr4+) to investigate their possible benefit for the ferroelectric properties of BiFeO3 ceramics. The cations with higher valence (Zr4+) ought to suppress the formation of structural defects during syntheses, such as oxygen vacancies and Fe2+. These defects are responsible for high leakage currents and low breakdown voltages characteristic of the pure BiFeO3. However, doping only with Zr did not improve the ferroelectric properties of bismuth ferrite. These samples were unable to persist electric fields above 30 kV/cm. On the other hand, the increase in lanthanum concentration resulted in improved ferroelectric and piezoelectric properties of the samples, sustaining electric fields above 100 kV/cm. Among the investigated samples, the highest remnant polarization of 24 μC/cm2 and piezoelectric coefficient (d33) of 34 pC/N reached Bi0.85La0.15FeO3 sample at 160 kV/cm. The share of non-ferroelectric contribution to the total polarization of this sample was the lowest (∼ 11 %). When it comes to the co-doped samples, the addition of Zr transformed the behavior from leaky ferroelectric to predominantly leaky dielectric. It indicated that doping with La significantly improved the ferroelectric properties of bismuth ferrite ceramics. In contrast, even a low Zr concentration of 1 mol% could outbalance the influence of much larger La concentrations (10 and 15 mol%).

Epitaxy of >7 μm Thick GaN Drift Layers on 150 mm Si(111) Substrates Realizing Vertical PN Diodes with 1200 V Breakdown Voltage

Metal‐organic chemical vapor deposition growth of vertical GaN PN structures on 6″ Si(111) substrates enabling a 1200 V breakdown voltage is demonstrated. Thanks to an optimized buffer structure utilizing island growth in an AlN/Al0.1Ga0.9N superlattice, the threading dislocation density is drastically reduced, and sufficient compressive stress is incorporated in active GaN layers to compensate for the thermal mismatch. Crack‐free PN structures with drift layer thicknesses up to 7.4 μm are realized with a threading dislocation density of ≈5 × 108 cm−2 and an absolute wafer bow <50 μm. Quasi‐vertical PN diodes reveal a linear increase in the breakdown voltage with the drift layer thickness with an average breakdown field of ≈1.6 MV cm−1. Additionally, the leakage current is shown to decrease monotonically as the drift layer thickness increases. For a 7.4 μm thick drift layer with a net ionized donor concentration of 0.9 × 1016 cm−3, a high breakdown voltage of 1200 V, a low specific on‐resistance of 0.4 mΩ cm−2, and a low leakage current of 10−4 A cm−2 (at a reverse bias of 650 V) are obtained. These results demonstrate the great potential of cost‐effective vertical GaN‐on‐Si power devices operating in the kilovolt range.

High-current, high-voltage AlN Schottky barrier diodes

AlN Schottky barrier diodes with low ideality factor (<1.2), low differential ON-resistance (<0.6 mΩ cm2), high current density (>5 kA cm−2), and high breakdown voltage (680 V) are reported. The device structure consisted of a two-layer, quasi-vertical design with a lightly doped AlN drift layer and a highly doped Al0.75Ga0.25N ohmic contact layer grown on AlN substrates. A combination of simulation, current–voltage measurements, and impedance spectroscopy analysis revealed that the AlN/AlGaN interface introduces a parasitic electron barrier due to the conduction band offset between the two materials. This barrier was found to limit the forward current in fabricated diodes. Further, we show that introducing a compositionally-graded layer between the AlN and the AlGaN reduces the interfacial barrier and increases the forward current density of fabricated diodes by a factor of 104.

Unconventional reservoir stimulation method based on electrohydraulic discharge shock and frequency resonance technology

To increase the production of unconventional oil and gas, it is necessary to improve reservoir porosity through reservoir reconstruction. High voltage electro-hydraulic discharge can generate strong shock waves, which not only meets the requirements of reservoir reconstruction, but also has the advantages of high efficiency and environmental protection, and has become a research hotspot. In order to further improve the effectiveness of reservoir transformation, a reservoir stimulation method based on electrohydraulic discharge shock and frequency resonance is proposed. Firstly, an electrohydraulic discharge equipment was designed, and according to the material and structure of the designed rod plate electrode, a theoretical electrohydraulic discharge model was built based on the bubble theory. The high voltage breakdown process under the condition of applied voltage of 12 kV and electrode gap of 2 mm is simulated in detail. The simulation results show that the discharge time is within 0.3 μs, and the extremely short discharge time not only produces strong shock waves, but also forms an arc channel to cause circuit damping oscillation. Then, an electrohydraulic discharge experimental platform was built according to the developed equipment. The discharge process was recorded by a high-precision oscilloscope, and the arc formation was photographed by a high-speed camera. The experimental results not only verify the correctness of the theoretical analysis, but also confirm that the developed electro-hydraulic discharge device can generate 0-60 Hz adjustable electrical pulses and has the ability to cause reservoir resonance. Finally, a comparative experiment was carried out with shale core samples to test the influence of resonance factors on the development of internal fractures in unconventional reservoir rocks. The CT scan images show that the shale fracture porosity in the resonance group increased by 46.4 %, which is much higher than that in the non-resonance group (11.8%). To further test the frequency resonance effect on reservoir reconstruction, a field test was carried out on the coalbed methane wells in Shanxi using the developed equipment. The experimental results show that the average gas production rate after on-site construction is increased from 11.46 m3/h to 12.49 m3/h, an increase of 8.99 %, indicating that the proposed technology can significantly promote the development of rock fractures and enhance the production recovery.

High-voltage kV-class AlN metal-semiconductor field-effect transistors on single-crystal AlN substrates

This letter reports the demonstration and electrical characterization of high-voltage AlN metal-semiconductor field-effect transistors (MESFETs) on single-crystal AlN substrates. Compared with AlN MESFETs on foreign substrates, the AlN-on-AlN MESFETs showed high breakdown voltages of over 2 kV for drain-to-gate spacing of 15 μm and one of the highest average breakdown fields among reported AlN MESFETs. Additionally, the devices also exhibited decent drain saturation current and on/off ratio without complicated regrown or graded contact layers, which are several times higher than those of reported AlN-on-sapphire MESEFTs. This work is beneficial for the future development of ultrawide bandgap AlN power electronics.

Low turn-on voltage AlGaN/GaN Schottky barrier diode with a low work function anode and high work function field plate

AlGaN/GaN Schottky barrier diodes (SBDs) with a low work function W anode and a high work function Ni field plate on sapphire substrates are investigated in this Letter. The low work function metal W leads to the low turn-on voltage, while the high work function metal Ni maintains the leakage current and increases the breakdown voltage. An ultralow turn-on voltage of 0.23 V determined by the positive fixed charge at the AlGaN/Si3N4 interface is achieved in this W/Ni SBD. More importantly, benefitting from the dual-metal anode/field plate structure, the on-resistance decreases from 7.99 to 5.53 Ω mm, and the breakdown voltage increases from 493 to 1219 V. In addition, the turn-on voltage decreases less than 57%, and the on-resistance increases less than 186% at a high temperature up to 120 °C. The W/Ni SBD with a cathode–anode length of 18 μm and a field plate length of 4 μm shows a low turn-on voltage of 0.23 V, a low on-resistance of 5.53 Ω mm, a leakage current of 0.65 mA/mm, and a high breakdown voltage of 1.21 kV, indicating a great potential for power electronic applications.

Review on Short-Circuit Protection Methods for SiC MOSFETs

SiC MOSFETs have been a game-changer in the domain of power electronics, thanks to their exceptional electrical traits. They are endowed with a high breakdown voltage, reduced on-resistance, and superior thermal conductivity, which make them supremely suitable for high-power and resilient applications across aviation, automotive, and renewable energy sectors. Despite their intrinsic advantages, SiC MOSFETs also necessitate advanced safeguarding mechanisms to counteract the vulnerability to short-circuit conditions due to their lower short-circuit robustness. This review paper offers an in-depth analysis of the array of short-circuit protection (SCP) methods applied to SiC MOSFETs. This paper scrutinizes techniques such as desaturation detection, di/dt detection, gate charge characteristics monitoring, two-dimensional monitoring, Rogowski coil-based detection, and two-stage turn-off strategies. The paper meticulously explores the operational principles, merits, and limitations of each method, with an emphasis on their adaptability to various fault types, including hard switching faults and load-induced faults. This review acts as a thorough compendium, guiding the choice of pertinent SCP strategies, ensuring the secure and efficient functioning of SiC MOSFETs in demanding applications.

Improving the suppression of charge movement by porous chromium oxide coating

A chromium trioxide coating was prepared on the surface of electronic ceramics by screen printing, and solid-phase sintering was carried out at 1350 °C. The surface roughness and surface resistance characteristics of composite coatings with different chromium trioxide contents were studied. The analysis results indicate that the average thickness of Cr2O3 coating is about 19.89 μm. The main crystal phase is (Al0.9Cr0.1)2O3. SEM shows that the surface "pores" and surface roughness of the coating change with the content of Cr2O3. AFM shows that when the Cr2O3 content in the coating is 0.0921 mol, the surface roughness changes the most, and the corresponding surface resistivity of Al2O3 insulating ceramics decreases to the lowest, from 1016 Ω to 1012 Ω. An increase in surface roughness can lead to changes in the incidence angle of electrons, reducing the probability of electron surface collision. The lower the surface resistivity, the better the high-voltage breakdown resistance of vacuum ceramic devices, thereby improving the surface flashover performance of ceramics.

The influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes

In this work we present studies on the influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes. Obtained results shows substantial effect of oxygen partial pressure on the electrical properties of NiO/β-Ga2O3 heterojunction diodes. The diodes with NiO layers deposited in pure Ar shows Schottky-like I-V characteristics with low ideality factor of 1.05 and barrier height of 1.27 eV as well as low turn-on voltage close to 1V. On the other hand, diodes with NiO layer deposited in oxygen containing atmosphere shows typical p-n diode characteristics. The best electrical characteristics i.e. low on-state resistance of 2.85 mΩcm2, lack of defects and low ideality factor down to 1.07 at RT along with high breakdown voltage close to 900V without any junction termination, were obtained for diodes with NiO layers deposited at 50 % oxygen content. We have demonstrated that by optimization of oxygen partial pressure, the properties of NiO/β-Ga2O3 heterojunction diodes can be tuned and excellent electrical performance in terms of low-on state resistance, high breakdown voltage, low-leakage current and low ideality factor, can be obtained.

Design and evaluation of β-Ga2O3 junction barrier schottky diode with p-GaN heterojunction

A novel design for a junction barrier Schottky (JBS) diode based on a p-GaN/n-Ga2O3 heterojunction is proposed, exhibiting superior static characteristics and a higher breakdown capability compared to the traditional Ga2O3 Schottky barrier diode (SBD). By utilizing wide-bandgap p-type GaN, the β-Ga2O3 JBS diodes demonstrate a turn-on voltage (V on ) of approximately 0.8 V. Moreover, a breakdown voltage (V br ) of 880 V and a specific on-resistance (R on,sp ) of 3.96 mΩ·cm2 are achieved, resulting in a Baliga’s figure of merit (BFOM) of approximately 0.2 GW /cm 2. A forward current density of 465 A cm−2 at a forward voltage of 3 V is attained. The simulated reverse leakage current density remains low at 9.0 mA cm−2 at 800 V. Floating field rings, in conjunction with junction termination extension (JTE), were utilized as edge termination methods to attain a high breakdown voltage. The impact of β-Ga2O3 periodic fin width fluctuations on the electrical characteristics of JBS was investigated. Due to the enhanced sidewall depletion effect caused by p-type GaN, the forward current (I F ) and reverse current (I R ) decrease when the β-Ga2O3 periodic fin width decreases. The findings of this study indicate the remarkable promise of p-GaN/n-Ga2O3 JBS diodes for power device applications.