Gallium Nitride Power Devices Research Articles

(Invited) Recent Progress in Medium-Voltage Vertical GaN Power Devices

Vertical gallium nitride (GaN) power devices continue to garner interest in multiple power conversion applications requiring a medium-voltage (1.2 – 20 kV) capability. Currently, silicon carbide (SiC) is addressing this voltage range, however, with a comparable critical electric field and superior mobility, GaN is expected to offer advantages in applications where fast switching and avalanche breakdown response times are desired. While uses in electric vehicles, solid-state transformers, and renewable energy conversion are being actively explored, the potential of a vertical GaN device for electric grid protection in the form of an electromagnetic pulse arrestor is a unique proposition that requires very fast transient capabilities (<1 µs pulse widths with rise-times on the order of 10 ns). However, vertical GaN devices are significantly less mature than present SiC offerings. Specifically, low-doped, thick epitaxial growth of GaN via metal-organic chemical vapor deposition (MOCVD) still presents many challenges, and advancements in processing, manufacturability, and failure analysis are needed.In this work, we describe our efforts to address the above issues and advance the state-of-the-art in vertical GaN PN diode development. We have successfully demonstrated an MOCVD-grown, 50 µm thick, low-doped (<1015 cm-3) drift region on a GaN substrate that was processed into relatively large-area (1 mm2) PN diodes capable of achieving a 6.7 kV breakdown. Temperature-dependent breakdown was observed, consistent with the avalanche process. The devices consisted of a 4-zone step-etched junction termination extension (JTE), where the breakdown region was visualized via electroluminescence (EL) imaging. Ongoing work aims to scale the current capability of the medium-voltage diodes through a parallel interconnect design that negates defective or poor performing diodes. Further investigation of edge termination structures was explored using a bevel approach, where we studied the relationship between the bevel angle and p-doping. It was found that a very shallow angle of only 5° accompanied by a 500 nm p-region consisting of 3×1017 cm-3 Mg concentration resulted in a consistent 1.2 kV breakdown for an 8 µm thick, 1.6×1016 cm-3 doped drift region. EL imaging confirmed uniform breakdown, and temperature dependence was demonstrated. The bevel approach was then implemented on a diode structure with a 20 µm thick drift region capable of 3.3 kV breakdown, where an unclamped inductive switching (UIS) test was performed to evaluate the impact of a field plate design on avalanche uniformity and ruggedness.A parallel effort to establish a foundry process for vertical GaN devices has been underway. Initially, this focus was on comprehensive studies of GaN wafer metrology using capacitance-voltage (C-V) mapping, optical profilometry, and x-ray diffraction (XRD) mapping. A machine learning algorithm was implemented to identify defective regions and produce a yield prediction for each GaN wafer prior to processing. A hybrid edge termination structure consisting of implanted guard rings (GR) and JTEs was developed in coordination with a controlled experiment that varied the anode thickness, and therefore the remaining p-GaN after implantation. It was observed that thinner p-GaN regions under the JTE/GR region resulted in a significant (>100x) reduction in leakage current under reverse-bias conditions. This process has resulted in 1.2-kV-class devices with up to 18 A forward current for a 1 mm2 device with a specific on-resistance of 1.2 mOhm-cm2. The foundry effort has since been extended to 3.3-kV-class devices that utilize 25 µm thick drift layers with ~2-4×1015 cm-3 doping. These devices have demonstrated up to 3.8 kV breakdown with leakage currents <1 nA up to 3 kV. More than 40 wafers have been processed to date, resulting in >20,000 devices. Statistical variations in I-V and C-V characteristics will be discussed. Packaging process development and analysis are underway to develop electrical stress procedures and identify fundamental failure mechanisms. Finally, a pulse arrested spark discharge (PASD) setup, capable of up to 15 kV pulsed operation in 100 V steps, was implemented to quantify the time response of avalanche breakdown. Initial results on a packaged 800 V device showed a ~1 ns response time during breakdown, which reinforces the potential EMP grid protection applicability. This work was supported by the ARPA-E OPEN+ Kilovolt Devices Cohort directed by Dr.Isik Kizilyalli. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy of the United States Government.

Impact of parasitic elements on the power dissipation of Si superjunction MOSFETs, SiC MOSFETs, and GaN HEMTs

In power conversion systems, where higher switching frequencies are required for miniaturization, the selection of power switches with lower power loss becomes essential for achieving better efficiency. At higher switching frequencies, the parasitic elements of the power switch largely dictate the efficiency of the power electronic system. Hence, it becomes critical to investigate the impact of parasitic losses on overall efficiency. The parasitic components of the power transistor vary with the semiconductor technology and thus effects the power converter system differently. This paper compares three power switch technologies: Silicon (Si) based Superjunction (SJ) power MOSFET, Silicon Carbide (SiC) based power MOSFET, and Gallium Nitride (GaN) based HEMT, for three different voltage ratings: 650 V, 900 V, and 1200 V. The effect of the parasitic components on the converter efficiency has been demonstrated using an inductive clamped loading circuit implemented in LTSPICE. The results demonstrate that at a frequency of 200 kHz, the total power loss for 650 V power switches was 44 W, 108 W, and 127 W for GaN, SiC, and SJ, respectively. At 500 kHz, the total power loss for 1200 V power switches was 622 W and 720 W for GaN and SiC, respectively. Overall, the GaN technology provides lower power losses than SiC and SJ due to lower parasitic capacitance and on-resistance, indicating the potential of GaN power devices for higher voltage applications. This comparison enables a power engineer to select an appropriate power switch that ensures the best possible efficiency for a specific application.

(Invited) Application of Synchrotron X-Ray Topography Techniques to the Analysis of Defect Microstructures in Bulk GaN Substrates and Epilayers for Power Devices

Wide bandgap semiconductor gallium nitride (GaN), along with silicon carbide (SiC) are replacing silicon materials in the applications for power electronic devices. While SiC-based power technologies are based on bulk SiC substrates, GaN-based power technologies have until recently been based on GaN layers grown on foreign substrates such as sapphire, SiC and Si substrates. To achieve the full potential of GaN power devices, devices on bulk GaN substrates are desirable. In this review, the use of synchrotron X-ray topography techniques to evaluate defects and strain in bulk GaN substrates for vertical device development is presented. Ray tracing simulations is shown to effectively identify the Burgers vectors of all dislocations on X-ray topographs from GaN materials. Ammonothermal-grown GaN substrate wafers show the best quality among all the wafers. These wafers, which are free of basal plane dislocations (BPDs), have low curvature and threading mixed dislocations (TMDs) dominant among the TDs. However, certain ammonothermal substrates contain growth sectors with different impurity concentrations that are likely inherited from prior seed expansion growth runs. Patterned hydride vapor phase epitaxy (HVPE) GaN reveal a starkly heterogeneous distribution of dislocations with large areas containing low threading dislocation densities in between a grid of strain centers with higher threading dislocation densities and BPDs. These substrates also contain growth sector boundaries separating core regions growing in <11-22> directions and surrounding regions growing along [0001]. HVPE GaN substrates are characterized by high lattice distortion and dislocation densities of the order of 105-106 cm-2, which is much higher than 103-104 cm-2 of ammonothermal samples and dislocation-free areas in the patterned HVPE samples. Epitaxial growth and other processes involving heat treatment (including annealing) does not nucleate new defects but can result in interactions of dislocations (threading screw dislocations(TSDs)/threading mixed dislocations (TMDs)/threading edge dislocations (TEDs)) with point defects leading to changes in dislocation configurations. Mg-ion implantation for p-type doping does not change the distribution of dislocation but introduces lattice damage. By Rocking curve Analysis by Dynamical Simulation (RADS) analysis of X-ray rocking curves, the depth profile of strain can be obtained and correlated with doping profile. During annealing the implanted samples to heal lattice damage and activate the Mg ions, proper capping is necessary to limit loss of matter and introduction of additional lattice distortion. However, high pressure annealing has been shown to eliminate the need for capping. The effect on microstructure from other selectively area doping techniques such as etch and regrowth, diffusion and neutron transmutation will also be discussed.

Stability, Reliability, and Robustness of GaN Power Devices: A Review

Gallium nitride (GaN) devices are revolutionarily advancing the efficiency, frequency, and form factor of power electronics. However, the material composition, architecture and physics of many GaN devices are significantly different from silicon and silicon carbide devices. These distinctions result in many unique stability, reliability and robustness issues facing GaN power devices. This paper reviews the current understanding of these issues, particularly those related to dynamic switching, and their impacts on system performance. Instead of delving into reliability physics, this paper intends to provide power electronics engineers the necessary information for deploying GaN devices in existing and emerging applications, as well as provide references for the qualification evaluations of GaN power devices. The issues covered in this paper include the dynamic instability of device parameters (e.g., on-resistance, threshold voltage, output capacitance), the device robustness in avalanche, overvoltage and short-circuit conditions, the device's switching reliability and lifetime, as well as the device's ruggedness under radiation and extreme (cryogenic and elevated) temperatures. Knowledge gaps and immediate research opportunities in the relevant fields are also discussed.

Gallium Nitride Power Devices in Power Electronics Applications: State of Art and Perspectives

High-electron-mobility transistors based on gallium nitride technology are the most recently developed power electronics devices involved in power electronics applications. This article critically overviews the advantages and drawbacks of these enhanced, wide-bandgap devices compared with the silicon and silicon carbide MOSFETs used in power converters. High-voltage and low-voltage device applications are discussed to indicate the most suitable area of use for these innovative power switches and to provide perspective for the future. A general survey on the applications of gallium nitride technology in DC-DC and DC-AC converters is carried out, considering the improvements and the issues expected for the higher switching transient speed achievable.

Gallium Nitride Power Devices in Magnetically Coupled Resonant Wireless Power Transfer Systems

The main function of power devices is to convert electrical energy through high-speed switching, such as AC/DC, high and low voltage conversion, etc. Therefore, the performance of the device directly affects the performance of the power electronic device, thereby further affecting the conversion efficiency of electrical energy. The arrival of the 5G era has greatly increased the demand for gallium nitride (GaN). The development of the wireless communication market has made GaN play a key role in many aspects of human activities. The main aim of this article is to research the application of GaN power devices in magnetically coupled resonant wireless power transfer (WPT) systems. This paper first introduces the related concepts of GaN power devices, magnetic coupling resonance and WPT, and analyzes the construction of magnetic coupling resonance WPT system in detail. Secondly, the energy transmission structure is analyzed, the system is designed and the system loss is calculated and analyzed. The system loss experiment shows that by using the output capacitor of the GaN device, the dead time is optimized, the conduction loss of the switch tube is reduced, the efficiency of the converter device is improved, and the practical application of the GaN device is provided.

Gallium Nitride Power Devices: A State of the Art Review

Gallium Nitride Power Devices: A State of the Art Review

A GaN–Si hybrid integrated driver for narrow-pulse and high-current LiDAR applications

Light detection and ranging (LiDAR) is the most important active remote sensing tool and is widely used in civilian and military fields. There are a number of methods to drive laser diodes; the most common circuit topologies are capacitor-discharge resonant circuits. However, the performance of the silicon (Si)-based switching device limits the development of Light detection and ranging, such as the large figure of merit (FOM) and the stray inductance. Although different methods have been reported to resolve these problems, there are still great challenges in reducing the pressure on Light detection and ranging driver design. Hence, this work presents a gallium nitride (GaN)–Si hybrid integrated driver for a Light detection and ranging system. In the circuit, the switching power device uses GaN instead of a Si-based device, because GaN enables much better performance for pulsed-laser operation due to its near-ideal switching performance. Furthermore, a GaN push–pull driver stage between the GaN power device and the Si-based driver integrated circuit (IC) was innovatively introduced, which is integrated in the same chip with the GaN power device, thereby effectively reducing the parasitic parameters of the signal chain and enhancing the system reliability. The design and implementation of the Si-based IC and GaN IC are based on 0.18 µm 80–120 V Bipolar-CMOS-DMOS (BCD) technology and 0.5 µm p-GaN technology, respectively. The experimental results suggest that the proposed driver circuit output pulse width is 12.6 ns, and it can normally operate at 10 MHz with turn-on/turn-off delay is 11.94 ns. In addition, the driver was capable of generating approximately 8.25 A current pulses through a low ohmic load with a pulse width of approximately 12.4 ns. This work plays a vital role in promoting the development of information equipment and aerospace equipment such as precise ranging, high-efficiency power supplies, and high-speed motors.

Dependence of reverse leakage on the edge termination process in vertical GaN power device

The trench gate metal oxide semiconductor field effect transistor (MOSFET) represents a prominent device architecture among the Gallium Nitride (GaN) based vertical devices currently investigated for the next generation of power electronics. A low leakage current level in off-state under high drain bias is of great importance for vertical transistors since it is a crucial feature for high breakdown voltage and device reliability. The off-state drain leakage originates from different sources in the vertical trench gate MOSFET. Besides the trench gate module, the leakage paths at the dry-etched sidewall of the lateral edge termination can also significantly contribute to the off-state drain-current. In this report, the influence of each relevant process step on the drain leakage current in off-state that is related to the lateral edge termination is investigated utilizing specific test structures on high-quality GaN epitaxial material which mimic the lateral edge termination of the MOSFET. Electrical characterization reveals the sensitivity of the leakage current to plasma-related processes. A termination technology is presented that results in low leakage current while including thick dielectric layers from plasma-assisted deposition as intended for fabrication of a field plate structure over the edge termination.

Wide Band Gap Devices and Their Application in Power Electronics

Power electronic systems have a great impact on modern society. Their applications target a more sustainable future by minimizing the negative impacts of industrialization on the environment, such as global warming effects and greenhouse gas emission. Power devices based on wide band gap (WBG) material have the potential to deliver a paradigm shift in regard to energy efficiency and working with respect to the devices based on mature silicon (Si). Gallium nitride (GaN) and silicon carbide (SiC) have been treated as one of the most promising WBG materials that allow the performance limits of matured Si switching devices to be significantly exceeded. WBG-based power devices enable fast switching with lower power losses at higher switching frequency and hence, allow the development of high power density and high efficiency power converters. This paper reviews popular SiC and GaN power devices, discusses the associated merits and challenges, and finally their applications in power electronics.

Process engineering of GaN power devices via selective-area p-type doping with ion implantation and ultra-high-pressure annealing

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the effective acceptor concentration near the surface, which can be compensated for by sequential nitrogen ion implantation. Defect-assisted Mg diffusion to the deeper region causes a redistribution of the Mg atoms and should be considered in the design of a device. Such anisotropic diffusion of Mg to the c-axis has potential applications in the fabrication of unique vertical device structures such as super junctions.

Recent progress on the vertical GaN power transistor and its integrated circuit

<p indent="0mm">Silicon (Si) material is the mainstream semiconductor material for a long time because of its relatively excellent high-temperature resistance, radiation resistance, low price, and huge reserves. However, with the rapid development of power electronics technology, the development of technology has reached a bottleneck period, and Moore’s law has gradually failed. The existing silicon-based semiconductor devices are close to the theoretical limit of Si materials and can no longer meet the performance requirements of future power devices. However, the cost of transistors is constantly rising, and the performance improvement is slow, gradually moving towards the post-Moore era. To further improve the performance of the device, it is necessary to seek new technologies or new materials to support the continuous development of power devices, and the core of the progress of power semiconductor devices is the development of semiconductor materials. As the third generation of wide band gap semiconductors, gallium nitride (GaN) has been superior to Si in terms of material properties. GaN has the advantages of a wide band gap, high critical field strength, high electron saturation velocity, high conductivity, high-temperature resistance, and high voltage resistance. Compared with traditional Si-based power devices, it not only has higher breakdown voltage, low on-resistance, high electron mobility and good thermal conductivity, but also has smaller device volume and better heat dissipation performance under the same performance, which greatly reduces power consumption and achieves the effect of energy saving and emission reduction. The cost of early GaN single crystal preparation and epitaxial growth is beyond reach. However, with the mature development of growth technology, not only the cost of GaN single crystal substrate and its epitaxial growth is decreasing, but also the quality is gradually increasing, which lays a solid foundation for the wide application of GaN power devices in the future. This paper lists the main physical parameters of GaN and other semiconductor materials, the preparation of GaN single crystal, and the main methods of its epitaxy growth, and describes the advantages of GaN power devices in the current environment. For the device structure, the problems of the lateral device and the advantages of the vertical device are listed, and why the vertical device can become the mainstream structure of future power devices is explained. On this basis, the structure, working principle, research progress, and existing problems of vertical current aperture GaN transistor (CAVET), trench GaN MOSFET, vertical trench MOSFET based on <italic>in-situ</italic> oxidation GaN interlayer (GaN OG-FET), and vertical GaN fin field effect transistor (GaN FinFET) are introduced in detail. The performance parameters of vertical GaN power transistors mentioned in this paper are summarized in tables according to device types and time sequence, and the general direction of the development of GaN power transistors in the future is proposed. For integrated circuit systems, the special requirements and key technologies of GaN power devices in driver chips are summarized. Finally, for the current market environment, listing the vertical GaN power transistor in the medium and low voltage range is a more popular and promising application scenario.

Review of Pulse Test Setup for the Switching Characterization of GaN Power Devices

Pulse test techniques are widely adopted in characterizing both the static and dynamic performances of semiconductor devices considering various device structures and operating conditions. For gallium nitride (GaN) devices, due to the current collapse phenomenon, fast and accurate measurement of their key electrical parameters, such as dynamic ON-state resistance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {ds}, \mathrm{\scriptscriptstyle ON}}$ </tex-math></inline-formula> , switching rising time, fall time, switching losses, and short-circuit (SC) robustness, becomes essential. This article presents a comprehensive review of state-of-the-art pulse test setup methods such as the double-pulse test (DPT), multiple-pulse test (MPT), and SC test (SCT) for the first time, which facilitates the GaN device structure design and practical applications in high efficiency and power density power converters.

Evaluation of GaN HEMTs in H3TRB Reliability Testing

Gallium Nitride (GaN) power devices can offer better switching performance and higher efficiency than Silicon Carbide (SiC) and Silicon (Si) devices in power electronics applications. GaN has extensively been incorporated in electric vehicle charging stations and power supplies, subjected to harsh environmental conditions. Many reliability studies evaluate GaN power devices through thermal stresses during current conduction or pulsing, with a few focusing on high blocking voltage and high humidity. This paper compares GaN-on-Si High-Electron-Mobility Transistors (HEMT) device characteristics under a High Humidity, High Temperature, Reverse Bias (H3TRB) Test. Twenty-one devices from three manufacturers were subjected to 85 °C and 85% relative humidity while blocking 80% of their voltage rating. Devices from two manufacturers utilize a cascade configuration with a silicon metal-oxide-semiconductor field-effect transistor (MOSFET), while the devices from the third manufacturer are lateral p-GaN HEMTs. Through characterization, three sample devices have exhibited degraded blocking voltage capability. The results of the H3TRB test and potential causes of the failure mode are discussed.

A perspective on multi-channel technology for the next-generation of GaN power devices

The outstanding properties of Gallium Nitride (GaN) have enabled considerable improvements in the performance of power devices compared to traditional silicon technology, resulting in more efficient and highly compact power converters. GaN power technology has rapidly developed and is expected to gain a significant market share in an increasing number of applications in the coming years. However, despite the great progress, the performance of current GaN devices is still far from what the GaN material could potentially offer, and a significant reduction of the device on-resistance for a certain blocking voltage is needed. Conventional GaN high-electron-mobility-transistors are based on a single two-dimensional electron gas (2DEG) channel, whose trade-off between electron mobility and carrier density limits the minimum achievable sheet resistance. To overcome such limitations, GaN power devices including multiple, vertically stacked 2DEG channels have recently been proposed, showing much-reduced resistances and excellent voltage blocking capabilities for a wide range of voltage classes from 1 to 10 kV. Such devices resulted in unprecedented high-power figures of merit and exceeded the SiC material limit, unveiling the full potential of lateral GaN power devices. This Letter reviews the recent progress of GaN multi-channel power devices and explores the promising perspective of the multi-channel platform for future power devices.

Study of Single Event Burnout Mechanism in GaN Power Devices Using Femtosecond Pulsed Laser

Single event burnout (SEB) is a great threat to gallium nitride (GaN) power devices for aerospace applications. This paper is dedicated to the investigation of the SEB mechanism in a GaN power device using a femtosecond pulsed laser. In the test, the SEB of a commercial p-GaN power device was triggered by a focused laser beam with a wavelength of 620 nm, and the irradiation-sensitive area of the devices was identified. We observed that the damage modes were consistent with the results of heavy ion experiments. The vertical breakdown of the drain is proposed as the dominant mechanism of SEB. We also provide a schematic representation of the leakage path formation using the electrical data obtained following laser-induced SEB. This study provides an important reference for consideration of device reliability and application prospects.

Comparative analysis of Si, SiC and GaN based quasi impedance source inverter

The impedance source inverter reduces the number of stages of energy conversion due to its ability to increase the output voltage. Silicon based semiconductor power devices are commonly used for inverters, but as the voltage and current rating of the inverter increases with demand for high efficiency, the Silicon Carbide and Gallium Nitride power devices are most preferred. These wide bandgap devices enable the switches to be operated at high switching frequencies and with the increase in switching frequency, the size of the impedance network elements present in the inverter can be reduced. Thus, obtaining a compact and highly efficient inverter module. This paper presents a comparative analysis of Silicon, Silicon – Carbide and Gallium Nitride based quasi – impedance source inverters through simulation study. The performance of the inverters is analysed based on its efficiency, voltage stress and current stress across the switches and the results are validated.

High-energy proton radiation effect of Gallium nitride power device with enhanced Cascode structure

To ascertain the damage mechanism caused by high-energy proton irradiation to AlGaN/GaN power devices of enhanced Cascode structures, we study the radiation effect of enhanced Cascode structure and depletion AlGaN/GaN power devices by using 60 MeV energy protons in this work. In the case of proton injection reaching 1×10&lt;sup&gt;12&lt;/sup&gt; p/cm&lt;sup&gt;2&lt;/sup&gt;, the experimental results show that the threshold voltage of the Cascode type device is negatively drifted, the transconductance decreases, and the peak leakage current increases. The threshold voltage decreases from 4.2 V to 3.0 V, with a decrement of 1.2 V, and the peak transconductance value decreases from 0.324 S/mm to 0.260 S/mm, with a decrement of about 19.75%. There is no significant change after the conventional depleted AlGaN/GaN device has been irradiated. The Cascode-type AlGaN/GaN power device is more sensitive to proton irradiation than the depletion-type AlGaN/GaN device. The Cascode-type device is sensitive to proton irradiation because of its structure connected to a silicon-based MOS tube. Proton irradiation causes the silicon-based MOS gate oxide layer to generate a large amount of net positive charge, induces an ionization damage effect, and causes threshold voltage to negatively drift and the gate leakage current to increase. The equivalent 60 MeV energy protons and cumulative injection of 1×10&lt;sup&gt;12&lt;/sup&gt; p/cm&lt;sup&gt;2&lt;/sup&gt; dose of the &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ {}_{}{}^{60}\rm{C}\rm{o}~\rm{\gamma } $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; radiation device is used to obtain the ionization damage effect. It is found that after being irradiated by the equivalent dose &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}${}_{}{}^{60}\rm{C}\rm{o}~\rm{\gamma }$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ray , the device has the threshold voltage decreasing from 4.15 V to 2.15 V, with a negative drift of 2 V; transconductance peak decreases from 0.335 S/mm to 0.300 S/mm, with an approximate decrement of 10.45%. The degradation of the electrical properties of the device after being irradiated by &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}${}_{}{}^{60}\rm{C}\rm{o}~\rm{\gamma }$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221617_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ray is consistent with the degradation law after being irradiated by high-energy protons. In order to further verify the experimental accuracy and conclusions, the ionization energy loss and non-ionization energy loss induced by radiation in the device are obtained by Monte Carlo simulation. The simulation results show that the ionization energy loss induces silicon-based MOS to generate oxide trap charge and interfacial state trap charge, which is mainly responsible for the performance degradation of AlGaN/GaN HEMT power devices with enhanced Cascode structure.

Design and Analysis of DC/DC Boost Converter Vertical GaN Power Device based on Epitaxially Grown GaN-on-sapphire

In this study, a high-performance vertical gallium nitride (GaN) power transistor was designed by using two-dimensional technology computer-aided design simulator. In addition, the vertical GaN transistor is used to analyze the DC/DC boost converter. Systems requiring high voltages of 1000 V or more, such as electric vehicles, need wide devices to achieve a high breakdown voltage when using conventional power devices. However, vertical GaN transistors can be fabricated with a small device area and a high breakdown voltage. The proposed device has an off-current of 413 pA/㎠, an on-current of 22 kA/㎠, and a high breakdown voltage of 1693 V due to good gate controllability and the undoped-GaN layer. The designed device was used to construct a boost converter that doubled the input voltage and its characteristics were examined. The boost converter produced an output voltage of 1955 V and the voltage conversion efficiency was high at 97.75 %.

(Invited) Development of Vertical Gallium Nitride Power Devices for Use in Electric Vehicle Drivetrains

The rapid acceleration of vehicle drivetrain electrification is expected to be a major driver for the widespread adoption of silicon carbide (SiC) power devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and junction-barrier-Schottky (JBS) diodes (the latter needed as the freewheeling diode in parallel with the MOSFET switch), due to their ability to increase the efficiency and reduce the volume of the power electronic inverter that ties the vehicle’s battery to the electric motor(s). The move from traditional silicon-based power electronics to SiC-based power electronics is necessary to achieve the U.S. Department of Energy (DOE) power electronics density target of 100 kW/L. However, gallium nitride (GaN)-based inverters may offer additional benefits beyond what can be achieved with SiC. For example, genetic-algorithm-based system-level simulations of the Pareto front trade-off between power density and efficiency of the inverter indicate that GaN power devices offer solutions superior to those achievable with SiC. However, given that the drivetrain DC bus voltage in future electric vehicles is expected to be 800 V or higher, commercially-available GaN power switching high electron mobility transistors (HEMTs), which typically have voltage ratings of 650 V or less, are unsuitable for a two-level inverter design, which is preferred by automotive system designers due to its simplicity and associated reliability. As such, vertical GaN power devices with voltage ratings of 1.2 kV or greater are necessary. This talk will describe our team’s efforts to develop both vertical GaN MOSFETs and JBS diodes. Designs for both trench MOSFETs and double-well MOSFETs (DMOSFETs) will be discussed. Experimental work has focused on trench MOSFETs, chiefly due to the need for selective-area doping in the DMOSFET, which is generally challenging in GaN and is particularly so in this structure due to the double well. The trench MOSFET presents significant challenges as well, including the need for a high-quality gate dielectric on the etched sidewall of the trench as well as mitigation of high electric fields at the bottom of the trench. Vertical GaN trench MOSFETs utilizing drift layers grown by metal-organic chemical vapor deposition (MOCVD) on native GaN substrates have been fabricated. Devices with an atomic-layer-deposited SiO2 gate dielectric have demonstrated a positive threshold voltage of ~8 V, an on/off ratio of ~108, and a current density of ~400 mA/mm. Additionally, GaN JBS diodes are being developed concurrently, and in this case selective-area doping cannot be avoided as alternating regions of p- and n-doped material are inherent to the operation of the device. Our team has utilized an etch-and-regrowth approach to demonstrate vertical GaN JBS diodes with reverse hold-off voltage >1.5 kV and forward turn-on voltage <1 V, consistent with JBS operation, although the reverse leakage current is higher than is typically observed for a continuously-grown GaN PN junction. Prospects to further improve device performance will be discussed, including reducing the reverse leakage current though advances in the selective-area p-GaN regrowth process. This work was supported by the Electric Drivetrain Consortium managed by Susan Rogers of DOE’s Vehicle Technologies Office and by the ARPA-E PNDIODES program directed by Isik Kizilyalli. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.