GaN Power Electronics Research Articles

SPICE Modelling-Assisted evaluation of dynamic on-resistance characterization in Schottky p-GaN HEMTs amid synchronous buck transient instabilities

This study addresses the critical gap in dynamic on-resistance characterization for GaN HEMTs within the initial unstable state in a non-isolated DC-DC converter, where the output voltage and currents fluctuate and exhibit overshoots or undershoots before stabilizing to their steady-state values, a domain within solar photovoltaic (PV) Maximum Power Point Tracking (MPPT) implementations which is crucial yet insufficiently examined. The authors present a novel multi-pulse test circuit within a synchronous buck converter configuration, complemented by SPICE simulation. This combination allows for the accurate assessment of clamping circuits' performance during transient states, significantly improving the precision of RDS(ON) measurements in unsteady phases. The approach deviates from conventional methods by merging empirical data with simulation insights to validate the efficacy of clamping circuits. The experimental results affirm the methodology's precision, with the highlighted Circuit V showcasing a marginal deviation of 2.32 % from existing benchmarks. This finding substantiates the method's dependability and practicality contributing to the GaN power electronics field. In addition, this research provides a powerful analytical tool for RDS(ON) evaluation, culminating in the design of a test PCB that synergizes with both simulated and empirical evidence, contributing future research in GaN HEMT power converter applications.

Ion-implanted triple-zone graded junction termination extension for vertical GaN p-n diodes

We demonstrate an ion-implanted triple-zone junction termination extension (JTE) for vertical GaN p-n diodes. Due to the spatial distribution of fixed charge in the triple-zone JTE structure, the peak electric fields at the contact metal edge and at the edge of the JTE are significantly reduced compared to conventional approaches. The forward and reverse characteristics of diodes with conventional single-zone JTE and the triple-zone JTE explored here have been studied and compared experimentally. GaN p-n diodes fabricated using the triple-zone JTE obtain an experimentally measured maximum breakdown voltage of 1.27 kV, appreciably higher than the 1.01 kV achieved using the single-zone JTE structure. The triple-zone JTE design also provides a wider window for fabrication processing and epitaxial wafer growth to achieve the high breakdown voltage compared to single-zone designs. The triple-zone JTE is promising for cost-effective fabrication of GaN power electronics.

ICeGaNTM technology: The easy-to-use and self-protected GaN power IC

• Three types of integration exist in the market of GaN Power Electronics. • New offering, ICeGaN TM , features an optimal level of integration. • Based on a smart interface for reliable, safe and ease-of-use of the GaN transistor. • ICeGaN can achieve much higher power densities in the system compared to Silicon. • ICeGaN can operate cooler and allow reduced bill of material compared to other GaN. This work provides an overview of the current state of technology in the field of lateral GaN power devices and presents the characteristics of the main commercially available 650V GaN power devices and ICs. A comparison is given, both in terms of key parameters as well as of the availability of complex functionality through integration of additional smart features. The features of our new technology, termed ICeGaN™, are presented in this context, focusing on the benefits that may be derived when ICeGaN™ devices are used in common applications. ICeGaN™ is a new concept of a smart HEMT which offers ease-of-use, sensing and protection functions without sacrificing performance.

(Invited) Advances in High Power, High Voltage, Reliable GaN Products for Multi Kilo-Watt Power Conversion Applications.

Gallium Nitride has been proven to be a superior material system for high performance, reliable, high power transistors enabling high efficiency in power conversion applications [1,2]. In this paper we highlight some recent advances in GaN technology which expand the capabilities and applications of GaN power switches.Transphorm, Inc, is a pioneer and leader in GaN power electronics with a wide product portfolio of products spanning <100W to >10kW applications with JEDEC and AEC-Q101 qualified products including qualified 650V and 900V products (Fig. 1), as well as demonstrated 1200V devices in development. Transphorm’s vertical integration allows for control over device design, GaN epitaxial growth, and device fabrication resulting in industry leading performance and reliability.Transphorm’s breadth of volume production applications from 45 W through 10 kW is in part due to its impressive Failure in Time (FIT) rate of < 0.3 failures per billion hours is based on Field Reliability Data collected over 40 billion hours.[3]Transphorm’s normally-off devices are built by combining a state-of-the-art high voltage (HV) GaN HEMT with a low voltage (LV) Silicon MOSFET into a cascode GaN FET configuration to offer superior reliability, performance, and ease of use. The LV Si MOSFET features low gate charge and high threshold voltage which makes for a very easy to drive switch with a large gate voltage drive margin and the HV GaN HEMT offers high performance due to the superior material and transport properties of GaN combining the best of both materials.The latest GenV 15 mΩ 650V SuperGaN® FET (TP65H015G5WS) is the lowest Ron packaged GaN FET in the market enabling >10kW output powers with a single switch [4]. Inductive switching waveforms in a half-bridge at 400 V/65 A for the SuperGaN FET and SiC MOSFET were compared (Fig. 2) and the GaN device delivered current and voltage switching speeds of 4 kA/μs and 60 kV/μs which is about 2x faster than that of the SiC MOSFET, resulting in a 50% reduction in switching loss.To assess the performance of the SuperGaN FET vs similarly rated SiC MOSFETs and SiC JFETs, the devices were configured into a 240V:400V boost converter operating at 70kHz (Fig. 3). The GaN FET based boost converter was able to operate up to 12kW of output power with a maximum junction temperature of just 139 oC while the SIC MOSFET and JFET boost converters were limited 11kW and 9.2kW respectively due to junction temperature reaching 165oC. At 9.2Wk output power, the SuperGaN FET power loss was 38% and 21% lower than the loss in the SiC JFET and SiC MOSFET respectively. This combination of lower temperature and higher output power demonstrates the importance of the high efficiency of the SuperGaN FET.The unparalleled efficiency of Transphorm’s SuperGaN FETs has enabled to the development of unique products such as a 3KVA datacenter UPS released by and industry leading supplier, which is the smallest, lightest, and most powerful 3KA datacenter UPS on the market with 93.3% peak efficiency and 2.5x higher power density which enabled the form factor to shrink form a 2U to 1U enclosure.Until recently, commercial GaN power electronic devices have only available up to 650V with Transphorm’s qualified 900V GaN FET (TP90H050WS) device being the exception. We have recently announced a breakthrough in GaN technology with the demonstration of a 1200V, 70mΩ lateral GaN FET in a TO-247 packageThe 1200V GaN FET achieved > 99% peak efficiency in a 450V:900V synchronous boost converter operating at 50kHz which is similar to the peak efficiency of our 650V Gen IV and Gen V products. Additionally, the 1200V GaN FET achieved higher efficiency than a similarly rated state-of-the-art 1200V SIC MOSFET in a 900V:450V buck converter at 100kHz and 5.5kW (Fig 4) demonstrating GaN can excel in 1200V applications [5].[1] Y.F. Wu, J. Gritters, L. Shen, R.P. Smith, J. McKay, R. Barr, R. Birkhahn, “Performance and robustness of first generation 600-V GaN-on-Si power transistors”, The 1st IEEE Workshop on Wide Bandgap Power Devices and Applications, 6-10, Oct, 2013.[2] Parikh, Y.F. Wu, L.K. Shen, "Commercialization of High 600V GaN-on-Silicon Power Devices", Materials Science Forum, Vols. 778-780, pp. 1174-1179, October 2014. [3] https://www.transphormusa.com/en/gan-technology/#quality-reliability [4] C. J. Neufeld, Y.-F. Wu, S. Wienecke, R.P. Smith, Y. Huang, M. Kamiyama, J. Ikeda, T. Hosoda,B. Swenson and R. Birkhahn, “650V/780A GaN Power HEMT Enabling 10kW-Class High-efficiency Power Conversion”, IEEE 8th Workshop on Wide Bandgap Power Devices and Applications, 7-11 Nov. 2021.[5] Gupta, et al. IEEE International Symposium on Power Semiconductor Devices 2022 (accepted for publication) Figure 1

GaN-on-GaN p-i-n diodes with avalanche capability enabled by eliminating surface leakage with hydrogen plasma treatment

Traditional mesa terminations require precise angle design to reduce the electric field at the edge and surface treatment to reduce etch damage. Otherwise, the device usually suffers a premature breakdown. This work proposes the use of easy-to-implement hydrogen plasma treatment to solve the premature breakdown caused by mesa and demonstrates the avalanche capability in GaN-on-GaN p-i-n diodes. The breakdown electric field when the avalanche occurred was ∼2.3 MV/cm at room temperature for a GaN drift layer with a doping concentration of ∼7 × 1015 cm−3, which is consistent with the theoretical value. The temperature coefficient of the avalanche breakdown voltage of the devices was 4.64–4.85 × 10−4 K−1. This work shows a simple and effective approach to achieve avalanche capability in vertical GaN power devices, which can serve as an important reference for the future development of efficient and robust GaN power electronics.

The movement of the Fermi level in heavily C doped GaN

It is empirically well acknowledged that C doping makes GaN high-resistive. However, the detailed doping type and high-resistivity mechanisms of C doped GaN, which are extremely essential for GaN power electronics, still remain unclear. In this work, we clarify the mutative (from downward to upward) shift of the Fermi level and the n-type conductivity in heavily C doped GaN grown by MOCVD for the C concentration increases over a critical value, by combining photo-assisted KPFM and Seebeck coefficient measurements. We also discuss the reverse transition of Fermi level and ultimately n-type conductivity should be attributed to the self-compensation and other donor-type compensation centers introduced along with C doping.

(Invited) GaN Power Electronics and Associated Fundamental Limits

How does it impact the design principles of power electronics in ultra-wide bandgap semiconductors? What fundamentally different roles does a p-region play in a power electric device in comparison to a semi-insulating region, for example, in the popular GaN HEMT based power transistors? What are the practical fundamental limits for the unipolar devices such as Schottky Barrier Didoes without the help of p-type? What are the unique advantages a polar semiconductor family like GaN can offer? What is polarization doping and how is polarization-doping fundamentally different from impurity doping? I will reflect on our efforts in seeking answers to these questions in the past 20 years in GaN power electronic devices as well as realizing state-of-the-art devices; some example publications can be found in references 1-12.Our work has been in part supported by ARPAe SWITCHES, AFOSR FA9550-17-1-0048, and NSF DMREF 1534303, making use of shared facilities at CNF (NSF ECCS-1542081), CCMR (NSF MRSEC DMR-1719875) and equipment supported by DMR-1338010.

GaN Vertical-Channel Junction Field-Effect Transistors With Regrown p-GaN by MOCVD

We report an experimental demonstration of GaN-based vertical-channel junction field-effect transistors (VC-JFETs). A p-GaN regrowth by metalorganic chemical vapor deposition (MOCVD) and a subsequent self-planarization process were developed to fabricate the GaN VC-JFETs. Fin-like channel regions were patterned by electron beam lithography (EBL) and aligned to ${m}$ -plane or ${a}$ -plane. The electrical properties of lateral and vertical p-n junctions were characterized to verify the effectiveness of the p-GaN regrowth. Both VC-JFETs with ${m}$ -plane and ${a}$ -plane channels show decent gate modulation. We further discussed important factors that may affect the device performance including interfacial impurities and nonuniform acceptor distribution. This work highlights the successful demonstration of GaN VC-JFETs and lateral p-n junctions by an etch-then-regrow process, providing valuable information and reference for the further development of GaN power electronics.

Transmorphic epitaxial growth of AlN nucleation layers on SiC substrates for high-breakdown thin GaN transistors

Interfaces containing misfit dislocations deteriorate electronic properties of heteroepitaxial wide bandgap III-nitride semiconductors grown on foreign substrates, as a result of lattice and thermal expansion mismatches and incompatible chemical bonding. We report grain-boundary-free AlN nucleation layers (NLs) grown by metalorganic chemical vapor deposition on SiC (0001) substrates mediated by an interface extending over two atomic layers L1 and L2 with composition (Al1/3Si2/3)2/3N and (Al2/3Si1/3)N, respectively. It is remarkable that the interfaces have ordered vacancies on one-third of the Al/Si position in L1, as shown here by analytical scanning transmission electron microscopy and ab initio calculations. This unique interface is coined the out-of-plane compositional-gradient with in-plane vacancy-ordering and can perfectly transform the in-plane lattice atomic configuration from the SiC substrate to the AlN NL within 1 nm thick transition. This transmorphic epitaxial scheme enables a critical breakdown field of ∼2 MV/cm achieved in thin GaN-based transistor heterostructures grown on top. Lateral breakdown voltages of 900 V and 1800 V are demonstrated at contact distances of 5 and 20 μm, respectively, and the vertical breakdown voltage is ≥3 kV. These results suggest that the transmorphic epitaxially grown AlN layer on SiC may become the next paradigm for GaN power electronics.

Demonstration of 1.27 kV Etch-Then-Regrow GaN ${p}$ -${n}$ Junctions With Low Leakage for GaN Power Electronics

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.

Dopant profiling in p-i-n GaN structures using secondary electrons

We show that secondary electrons in a scanning electron microscope can provide important information about spatial dopant distribution in p-i-n GaN structures, with the highest contrast observed for a primary electron beam accelerating voltage in the range of 1 to 2 kV. The current through the specimen is used to determine the total backscattered and secondary electron yield. We establish a correlation between the secondary electron emission intensity and the doping characteristics of the material. The secondary electron emission intensity was found to be highest for p-type GaN, intermediate for n-type GaN, and lowest for undoped GaN. Specimen currents are found to have a strong correlation with the Mg concentration in p-GaN films. The contrast associated with dopants is shown to depend on experimental parameters such as primary electron beam voltage, total electron beam exposure, and specimen surface history. This technique can serve as a powerful tool for the development and characterization of thin films for GaN power electronics.

Implantation-and etching-free high voltage vertical GaN p–n diodes terminated by plasma-hydrogenated p-GaN: revealing the role of thermal annealing

Low-damage, low-temperature, and easy-to-implement hydrogen-plasma-based termination is attractive for fabricating implantation- and etching-free GaN power p–n diodes. This work investigates in detail the hydrogenation process and unveils the critical role of thermal annealing. A subsequent thermal annealing is key to thermally driving down hydrogen to fully hydrogenate p-GaN to form the termination. The devices showed a specific on-resistance of 0.4 mΩ cm2 and a breakdown voltage (BV) of ∼1.4 kV. They also exhibited improved BV compared with mesa-etched devices. High temperature performance was also investigated. These results can serve as important references for future developments of GaN power electronics.

Non-uniform Mg distribution in GaN epilayers grown on mesa structures for applications in GaN power electronics

A strong variation in the luminescence characteristics in Mg-doped GaN grown on mesa structures has been observed, with the sidewall luminescence being different from that of the flat regions. A comparison with the luminescence characteristics of Mg-doped GaN epilayers with different Mg concentrations indicates that the sidewall has a significantly lower Mg content. This observed non-uniform Mg distribution is attributed to the dependence of Mg incorporation efficiency on the crystal orientation of the growth surface, which should impact the electrical performance of power devices.

Thermal Management and Characterization of High-Power Wide-Bandgap Semiconductor Electronic and Photonic Devices in Automotive Applications

GaN-based high-power wide-bandgap semiconductor electronics and photonics have been considered as promising candidates to replace conventional devices for automotive applications due to high energy conversion efficiency, ruggedness, and superior transient performance. However, performance and reliability are detrimentally impacted by significant heat generation in the device active area. Therefore, thermal management plays a critical role in the development of GaN-based high-power electronic and photonic devices. This paper presents a comprehensive review of the thermal management strategies for GaN-based lateral power/RF transistors and light-emitting diodes (LEDs) reported by researchers in both industry and academia. The review is divided into three parts: (1) a survey of thermal metrology techniques, including infrared thermography, Raman thermometry, and thermoreflectance thermal imaging, that have been applied to study GaN electronics and photonics; (2) practical thermal management solutions for GaN power electronics; and (3) packaging techniques and cooling systems for GaN LEDs used in automotive lighting applications.

Investigation of GaN-on-GaN vertical p-n diode with regrown p-GaN by metalorganic chemical vapor deposition

To mimic selective-area doping, p-GaN was regrown on an etched GaN surface on GaN substrates by metalorganic chemical vapor deposition. Vertical GaN-on-GaN p-n diodes were fabricated to investigate the effects of the etch-then-regrowth process on device performance. The crystal quality of the sample after each epitaxial step was characterized by X-ray diffraction, where the etch-then-regrowth process led to a very slight increase in edge dislocations. A regrowth interfacial layer was clearly shown by transmission electron microscopy. Strong electroluminescence was observed with three emission peaks at 2.2 eV, 2.8 eV, and 3.0 eV. The forward current density increased slightly with increasing temperature, while the reverse current density was almost temperature independent indicating tunneling as the reverse transport mechanism. This result is very similar to the reported Zener tunnel diode comprising a high doping profile at the junction interface. High levels of silicon and oxygen concentrations were observed at the regrowth interface with a distribution width of ∼100 nm. This work provides valuable information on p-GaN regrowth and regrown GaN p-n diodes, which can serve as an important reference for developing selective doping for advanced GaN power electronics for high voltage and high power applications.

Nearly-zero valence band and large conduction band offset at BAlN/GaN heterointerface for optical and power device application

Wurtzite BAlN alloy with large bandgap is an emerging material system for UV optoelectronic and power devices. In this study, the BAlN/GaN heterojunction with a sharp interface and uniform distribution of the elements was formed by careful control of epitaxial conditions to avoid GaN desorption and parasitic reactions whose band alignment was then measured for the first time. The valence band offset (VBO) was found to be nearly-zero, i.e. −0.2 ± 0.2 eV, in the B0.14Al0.86N/GaN heterojunction by X-ray photoelectron spectroscopy. Additionally, the conduction band offset (CBO) is estimated at 2.1 ± 0.2 eV, which is the largest reported CBO among epitaxial GaN-based heterojunctions. In comparison to the type-I Al0.75Ga0.25N/GaN heterojunction (both Al0.75Ga0.25N and B0.14Al0.86N alloy have the same bandgap of 5.7 eV), the CBO and VBO of the B0.14Al0.86N/GaN heterostructure are significantly larger and smaller, respectively. The nearly-zero VBO and the very large CBO of the B0.14Al0.86N/GaN heterojunction could potentially lead to considerable performance enhancement for GaN optoelectronics and power electronics devices.

Mechanical Analysis of Stretchable AlGaN/GaN High Electron Mobility Transistors

Stretchable electronics are of interest for a variety of applications including wearable systems, soft robotics and medical diagnostics [1]. Creating devices and systems able to survive tens or hundreds of percent mechanical strain requires a shift to unconventional substrates such as silicone or polyurethane. Stretchable transistors based on silicon have been previously demonstrated based on thinning and lithographically patterning to relieve strain [1]. In this work, we investigate the possibility of using AlGaN/GaN high electron mobility transistors (HEMTs) in a similar stretchable system. One advantage of GaN based devices over Si devices is the higher critical field stemming from the wider bandgap of GaN compared to Si [2]. The higher critical field results in a lower specific on-resistance (Ron-sp) for a given breakdown voltage [3] shown in Figure 1 where AlGaN/GaN HEMTs are expected to have about a factor of 1000 lower Ron-sp for a given breakdown voltage. Thus the I2R power losses should be 1000 times less in GaN systems compared to Si systems for a given operating current. The lower Ron-spis of particular importance for wearable systems in close proximity to the skin where a temperature rise of just a few degrees can result in discomfort [4]. Semiconductors such as Si or GaN are rigid in nature and are not intrinsically stretchable. To render materials stretchable, device layers must be both sufficiently thin (~ 1 – 5 µm) and attached to stretchable substrates such as silicone. In addition, devices must have unique stretchable geometries such as a sinusoidal or horseshoe shape to relieve strain and prevent breakage. In this work, we have theoretically modeled the effects of device geometry on the mechanical properties of both GaN and Si using COMSOL finite element solver for the Hooke’s Law equation for continuous media using published values of the stiffness matrix and mass density of both Si [5] and GaN [6]. We examined straight, sinusoidal, horseshoe, rectangular and curve corner rectangular (CC-rectangular) device geometries for both materials with Sylgard 184 (Dow Corning) as a stretchable substrate [7]. Figure 2 shows our results with peak stress plotted as a function of peak to peak amplitude for multiple device geometries. Our results show that the peak stress for multiple device designs in GaN material is approximately 2.5 times larger than that of Si which can be attributed to the difference in Young’s Modulus and thus components of the stiffness tensor between the two materials. Because Si based devices have been rendered stretchable, our mechanical simulations suggest that GaN based devices such as the HEMT are also potential candidates for stretchable electronics. [1] D. Kim, N. Lu, R. Ma, Y. Kim, R. Kim, S. Wang, J. Wu, S. M. Won, H. Tao, A. Islam, K. J. Yu, T. Kim, R. Chowdhury, M. Ying, L. Xu, M. Li, H. Chung, H. Keum, M. McCormick, P. Liu, Y. Zhang, F. G. Omenetto, Y. Huang, T. Coleman and J. A. Rogers, “Epidermal electronics,” Science, vol. 333 838 (2011).[2] L. Bin, D. Piedra, and T. Palacios, “GaN power electronics,” 8th International Conference on Advanced Semiconductor Devices and Microsystems, (2010)105-110. [3] B.J. Baliga, “Fundamentals of Power Semiconductor Devices” Berlin: Springer, (2008).[4] H. Fruhstorfer, U. Lindblom, and W.G. Schmidt, “Method for quantitative estimation of thermal thresholds in patients,” J. Neurology, Neurosurgery, and Psychiatry, 39, (1976) 1071-1075.[5] J. Singh, “Electronic and Optoelectronic Properties of Semiconductor Structures,” Cambridge: Cambridge University Press pg. 35 (2003).[6] M. Rais-Zadeh, Mina et al. “Gallium Nitride as an Electromechanical Material”. Journal of Microelectromechanical Systems 23.6 (2014): 1252-1271.[7] N. Lazarus, C. D. Meyer and S. S. Bedair, “Stretchable inductor design,” IEEE Trans. on Electron Devices, 62 2270 (2015). Figure 1

(Invited) High-Power AlGaN/GaN Heterostructure Field-Effect Transistors on 200mm Si Substrates

Crack-free AlGaN/GaN heterostructure field-effect transistors on a 200 mm silicon substrate were demonstrated to enable large-volume, low-cost manufacturing technology for GaN power electronics. Low normalized buffer leakage of around 3 × 10-9 A/mm and low normalized three-terminal subthreshold leakage of around 2 × 10-7 A/mm were obtained using highly carbon-doped buffer epilayers. A high three-terminal off-state breakdown voltage of 1.35 kV and a low specific on-resistance of 1.3 mohm-cm2 were achieved on the 4.5-µm-thick device with a 10 µm gate-to-drain spacing. The figure of merit of our device is calculated as 1.4×109 V2ohm-1cm-2

Plasma MBE growth conditions of AlGaN/GaN high-electron-mobility transistors on silicon and their device characteristics with epitaxially regrown ohmic contacts

Silicon substrates offer an attractive substrate platform for GaN RF and power electronics. In this work, we address the key challenges and provide solutions for the RF-MBE growth of GaN high-electron-mobility transistors (HEMTs) on Si(111). Moreover, by developing low-leakage buffer layers and employing raised source/drain regrown ohmic contacts, high-performance HEMTs are realized at a significantly lower process temperature by plasma MBE than by MOCVD. This is expected to motivate further ideas for the integration of GaN with silicon that go beyond RF and power electronics into the regime of low-power digital logic by exploiting the unique polarization properties of GaN.

(Invited) Development of 4 Inch and 6 Inch GaN-on-Si for High-Voltage Operation

4 inch and 6 inch GaN-on-silicon (GOS) epitaxial wafers have been developed to enable large-volume, low-cost manufacturing technology for GaN power electronics. In an effort to reduce the buffer leakage and improve the buffer blocking voltage as well as the device off-state breakdown voltage, carbon-doped buffer epilayers and total nitride epitaxy thickness were investigated. Low normalized buffer leakage of around 3 × 10-9 A/mm and low normalized three-terminal subthreshold leakage of around 2 × 10-7 A/mm with on/off ratio of ~106 were obtained from both 4 and 6 inch GOS HEMT wafers. A three-terminal off-state breakdown voltage of 1.2 kV was achieved on a GOS HEMT with 10 μm GD spacing to confirm a strong potential for high power applications.