Differential On-resistance Research Articles

High-Temperature Characteristics of 3-kV 4H-SiC Reverse Blocking MOSFET for High-Performance Bidirectional Switch

Novel 3-kV 4H-SiC reverse blocking (RB) metal–oxide–semiconductor field-effect transistors (MOSFETs) have been demonstrated for high-voltage bidirectional switching applications. To achieve RB capability, a series Schottky barrier diode structure was introduced onto the backside of the 4H-SiC MOSFET. The developed SiC RB MOSFET exhibits bidirectional blocking voltage over 3 kV and a differential specific on-resistance of 20 $\text{m}\Omega ~\cdot $ cm2 at room temperature. In an inductive-load switching measurement, the RB MOSFET showed good turn-ON/-OFF characteristics at 1 kV. The bidirectional switch configured by the developed RB MOSFETs exhibited lower ON-state power loss than the series connection of the standard SiC MOSFETs at wide range of temperature and operation current, demonstrating the advantage of the SiC RB MOSFET as a high-performance bidirectional switch.

(Invited) AlGaN-Based PN Diodes for Power Electronics

As the performance of GaN- and SiC-based power devices becomes limited by fundamental material properties, semiconductors with larger bandgaps are appealing due to their superior material properties. Most notable is that the critical electrical field scales as the bandgap to the 2.0-2.5 power. Thus, diodes employing wide bandgap semiconductors are expected to operate at higher breakdown voltages with thinner and more heavily-doped drift regions, leading to lower resistive losses. AlGaN alloys with their much larger bandgap compared to SiC and GaN are thus appealing for high voltage pn diodes and transistors. Additionally, the formation of AlGaN-based heterojunctions and the utilization of polarization fields offer design options not possible for devices based on materials such as SiC and diamond. Here we report on the growth and performance of pn diodes fabricated from Al0.30Ga0.70N (Eg=4.1eV) and Al0.74Ga0.26N (Eg=5.3eV) alloys, illustrating the potential for AlGaN alloys as a viable material for next-generation power diodes. Quasi-vertical pn diodes consisting of Al0.30Ga0.70N epilayers were grown by metalorganic vapor phase epitaxy on 1.3 mm thick sapphire substrates. The added stiffness of such thick sapphire substrates (3x thicker than typical sapphire) reduces wafer bow and eliminates cracking in epitaxial structures up to 19 μm thick. Thick epitaxial structures are needed to achieve the > 4 microns thick drift layers necessary for multi-kilovolt breakdown voltages. A series of pn diode structures were grown where the thickness of the lightly doped drift layer (No = 2-5x1016 cm-3) was varied from 4.3 to 11 μm. All structures were completed with a 0.35 μm thick Mg-doped Al0.30Ga0.70N p-layer followed by a compositional grade to a p-GaN contact layer. Diodes employed a junction edge termination structure around the p-contact to reduce the peak electric field at the contact metal to avoid premature breakdown. Breakdown voltages from 1600 to 3000V were achieved in reverse bias and a forward turn-on voltage of 6 to 8 volts was recorded. To our knowledge, this is the first vertical AlGaN-based pn diode exhibiting a breakdown voltage in excess of 1 kilovolt. The differential specific on-resistance was higher than expected based on consideration of the drift region only (typically 16-20 mΩ-cm2), which is tentatively attributed to the resistance due to lateral current spreading in these front-contacted, quasi-vertical diodes. An effective critical electric field of 5.9 MV/cm was determined from the reverse current-voltage characteristics based on a punch-through, as dictated by the doping and thickness of the drift region. We have also investigated quasi-vertical pn diodes consisting of Al0.74Ga0.26N epilayers to exploit the expected higher critical electric field in higher aluminum mole fraction alloys. These diodes consisted of 4.5 μm thick AlN epilayers grown on sapphire followed by a heavily doped n-type contact layer. Next a lightly doped (No = 2-4x1016 cm-3) 5 or 8 μm thick drift layer was grown. The combination of a thick AlN buffer and Al0.74Ga0.26N layers resulted in x-ray diffraction linewidths of 164-197 (237–284) arc seconds for the (0002) and (10-12) reflections for the drift layer, respectively. By optimizing the growth conditions used for the drift layer, the density of electron compensating defects can be reduced to ~ 1x1016 cm-3 — a level reported for GaN pn diodes. Unlike GaN diodes where drift layer doping at mid to low 1015 cm-3 is necessary for breakdown voltages of several kilovolts, the free electron concentration in these Al0.74Ga0.26N pn diodes is significantly higher than the level of compensation, making doping much easier to control and illustrating the benefit of higher critical electric field. The drift layer was followed by p-type AlGaN and finally a compositional grade to a p-GaN contact layer. It is the p-AlGaN layer that is a significant challenge in Al-rich pn diodes. Unlike pn diodes based on Al0.30Ga0.70N epilayers, simple homojunction pn diodes are not practical in Al-rich AlGaN alloys due to the low hole concentration owing to the very deep (Ea > 400 meV) acceptor level. Consequently, other approaches must be considered for hole transport to the pn junction. We will report on the current-voltage characteristics of pn heterojunction diodes where a Mg-doped p-type Al0.30Ga0.70N layer is grown on the n-type Al0.74Ga0.26N drift layer. Additionally, the current-voltage characteristics of pn diodes where holes are generated in the p-region by field ionization of Mg acceptors will also be presented. Finally, practical pn diodes require specific on-resistance lower than what is inherent for front-contacted quasi-vertical device architectures grown on insulating substrates. We will report an approach that has realized vertically conducting AlGaN pn diodes employing AlGaN overgrowth on conducting GaN substrates.

1.1-kV Vertical GaN p-n Diodes With p-GaN Regrown by Molecular Beam Epitaxy

High-voltage vertical regrown p-n junction diodes on bulk GaN substrates are reported in this letter with molecular-beam-epitaxy regrown p-GaN on metalorganic-chemical-vapor-deposition grown n-GaN drift region. The highest breakdown voltage is measured at 1135 V, and the differential on-resistance is 3.9 mOhm.cm2 at room temperature. The forward I–V show a turn-ON voltage near 3.9 V and an ideality factor of 2.5. Electroluminescence measurement of regrown p-n junctions shows ~30 times reduced emission intensity compared with as-grown p-n junctions, indicating presence of excessive non-radiative recombination centers introduced by the regrowth process. Temperature dependent reverse I–V measurements suggest that variable range hopping inside the depleted regrown p-GaN layer is likely the mechanism of the reverse leakage. This is the first high-voltage vertical regrown p-n junction ever reported in the GaN system.

10+ kV Implantation-Free 4H-SiC PiN Diodes

Implantation-free mesa etched 10+ kV 4H-SiC PiN diodes are fabricated, measured and analyzed by device simulation. An area-optimized junction termination extension (O-JTE) is implemented in order to achieve a high breakdown voltage. The diodes design allows a high breakdown voltage of about 19.3 kV according to simulations by Sentaurus TCAD. No breakdown voltage is recorded up to 10 kV with a very low leakage current of 0.1 μA. The current spreading within the thick drift layer is considered and a voltage drop (VF) of 8.3 V and 11.4 V are measured at 50 A/cm2 and 100 A/cm2, respectively. The differential on-resistance (Diff. Ron) of 67.7 mΩ.cm2 and 55.7 mΩ.cm2 are measured at 50 A/cm2 and 100 A/cm2, respectively.

A Novel Si–GaN Monolithic Integration Technology for a High-Voltage Cascoded Diode

In this letter, a novel approach for monolithic integration of Si-based and GaN-based devices on Si substrate for high-voltage power switching applications is reported. To enable the integration, AlGaN/GaN epitaxial growth is carried out in recessed windows on a Si (111) substrate by selective epitaxial growth. A cascoded diode formed by series connection of a Si diode and a normally- ON AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor is experimentally demonstrated by using this technology. The cascoded diode features a breakdown voltage of 557 V and a differential specific ON-resistance of 2.8 $\text{m}\Omega \cdot $ cm2 at 500 A/cm2. Its reverse leakage current is two orders of magnitude lower compared with the conventional AlGaN/GaN Schottky barrier diode. The characterization results of the fabricated cascoded diode demonstrate that the proposed Si–GaN monolithic integration technology is compatible with both Si and GaN fabrication processes.

Fully- and Quasi-Vertical GaN-on-Si p-i-n Diodes: High Performance and Comprehensive Comparison

We report growth and fabrication of fully- and quasi-vertical GaN-on-Si p-i-n diodes. A record high Baliga figure of merit of 304 and 152 MW/cm2 is reported for fully- and quasi-vertical GaN-on-Si p-i-n diodes, respectively. A comprehensive comparison has been made between the two kinds of diodes in regard ON-resistance, breakdown voltage, and switching performance. An ultralow differential ON-resistance of 0.5 and 1.0 $\text {m}\Omega \cdot \text {cm}^{2}$ has been demonstrated for quasi- and fully-vertical diodes with a diameter of 60 $\mu \text{m}$ at 3 kA/cm2. Current crowding effect in the n-GaN was a dominant factor of RON, especially for large size quasi-vertical diodes at high current density. A high Vbr of 390 V has been demonstrated for the two types of device structures, regardless of device diameters. The same breakdown voltage and low off-state leakage indicated the reliability of fully-vertical device fabrication that reflects intrinsic properties of the grown epilayers. The two kinds of diodes share similar switching performance, which is much superior to a commercial fast-recovery Si diode as a reference. The device characteristics show promising potential of both fully- and quasi-vertical diodes for low-cost high-power applications.

High-Performance 500 V Quasi- and Fully-Vertical GaN-on-Si pn Diodes

This letter demonstrates quasi- and fully vertical GaN-on-Si pn diodes with record performance. The optimized device structure employs a highly conductive (N D >10 20 cm -3 ) current collecting layer and a lightly carbon-doped drift layer. With this optimization, a differential specific on-resistance (R ON ) of 0.8-1 mΩ·cm 2 , a breakdown voltage (BV) over 500 V, and a high forward current (~kA/cm 2 ) were demonstrated. Excellent R ON and BV performance up to 300 °C were also obtained. A small reverse recovery time of 50 ns was demonstrated under switching conditions. With Baliga's figure of merit over 0.32 GW/cm 2 , these devices show the great potential of low-cost GaN-onSi vertical devices for future power applications.

4H-SiC trench IGBT with lower on-state voltage drop

In this paper, a new 4H-SiC trench-gate IGBT structure incorporated a P+ shielding region in the emitter side is proposed in order to reduce the on-state voltage drop. Through the 2-D ATLAS simulation, the characteristics of the proposed structure are investigated and compared with the conventional structure. The simulation results indicate that the proposed structure exhibits an improvement in the following. Firstly, the on-state voltage drop is reduced by 32.75%. Secondly, the differential specific on-resistance is reduced by 42.33%. Finally, under the same on-state voltage drop, the turn-off energy is reduced more than 50.00%. At the end of the paper, it is explored that what effects the physical parameter of the P+ shielding region in the proposed structure have on the steady state performances.

Experimental Demonstration of High-Voltage 4H-SiC Bi-Directional IGBTs

We experimentally demonstrate, for the first time, bi-directional 4H-SiC planar gate, insulated gate bipolar transistors fabricated on 250- $\mu \text{m}$ thick, lightly doped free-standing substrates. On Si face, forward voltage drop (at 50 A/cm $^{2})$ of 9.7 V was obtained at room temperature, with a differential ON-resistance of 140 $\text{m}\Omega \cdot \text {cm}^{2}$ , indicating good conductivity modulation. We have also demonstrated control over minority carrier injection in static characteristics of the BD-IGBTs by application of a back-gate bias.

Al 0 .3 Ga 0.7 N PN diode with breakdown voltage >1600 V

Demonstration of Al0.3Ga0.7N PN diodes grown with breakdown voltages in excess of 1600 V is reported. The total epilayer thickness is 9.1 μm and was grown by metal-organic vapour-phase epitaxy on 1.3-mm-thick sapphire in order to achieve crack-free structures. A junction termination edge structure was employed to control the lateral electric fields. A current density of 3.5 kA/cm2 was achieved under DC forward bias and a reverse leakage current <3 nA was measured for voltages <1200 V. The differential on-resistance of 16 mΩ cm2 is limited by the lateral conductivity of the n-type contact layer required by the front-surface contact geometry of the device. An effective critical electric field of 5.9 MV/cm was determined from the epilayer properties and the reverse current–voltage characteristics. To our knowledge, this is the first aluminium gallium nitride (AlGaN)-based PN diode exhibiting a breakdown voltage in excess of 1 kV. It is noted that a Baliga figure of merit (V br 2/R spec,on) of 150 MW/cm2 found is the highest reported for an AlGaN PN diode and illustrates the potential of larger-bandgap AlGaN alloys for high-voltage devices.

Conduction Loss Reduction for Bipolar Injection Field-Effect-Transistors (BIFET)

In this study, the potential of forward conduction loss reduction of Bipolar-Injection Field-Effect-Transistors (SiC-p-BIFET) with an intended blocking voltage of 10kV by adjusting the doping concentration in the channel-region is analyzed. For the optimization of the SiC-p-BIFET, numerical simulations were carried out. Regarding a desired turn-off voltage of approximately 25V, the optimum doping concentration in the channel-region was found to be 1.4x1017cm-3. Based on these results, SiC-p-BIFETs were fabricated and electrically characterized in the temperature range from 25°C up to 175°C. In this study, the differential on-resistance was found to be 110mΩcm2 for a temperature of 25°C and 55mΩcm2 for a temperature of 175°C. In comparison to our former results, a reduction of the differential on-resistance of about 310mΩcm2 at room temperature is demonstrated.

6.5 kV n-Channel 4H-SiC IGBT with Low Switching Loss Achieved by Extremely Thin Drift Layer

Thin drift layers were used to realize n-channel 4H-SiC IGBTs with an extremely low switching loss. The thickness of a drift layer was 60 μm, which was designed for a blocking voltage of 6.5 kV. An on-voltage of 5.4 V was obtained at a collector current of 100 A/cm2 and the specific differential on-resistance at 100 A/cm2 was 20 mΩcm2 at room temperature, indicating proper bipolar operation. A switching evaluation of the SiC IGBTs was performed with a bus voltage of 3.6 kV and a load current of 10 A, and a turn-off loss of 1.2 mJ was obtained. This turn-off loss is very small compared to the values in the current literatures, and was estimated to be an over 80% reduction. The series operation of thin-drift-layer 6.5 kV SiC IGBTs can ensure a lower switching loss than the single operation of higher blocking voltage devices in power conversion systems.

Fully Vertical GaN p-i-n Diodes Using GaN-on-Si Epilayers

Using GaN-on-Si epilayers, for the first time, fully vertical p-i-n diodes are demonstrated after Si substrate removal, transfer, and n-electrode formation at the top of the device. After SiO2 sidewall passivation, the vertical p-i-n diodes, with n-GaN facing up, exhibit $V_{{\mathrm{\scriptscriptstyle ON}}}$ of 3.35 V at 1 A/cm2, a low differential on-resistance of 3.3 $\text{m}\Omega $ cm2 at 300 A/cm2, and a breakdown voltage of 350 V. The corresponding Baliga's figure of merit is 37.0 MW/cm2, a very good value for GaN-based p-i-n rectifiers grown on Si substrates. The results indicate that fully vertical rectifiers using GaN-on-Si epilayers have great potential in achieving cost-effective GaN devices for high-power and high-voltage applications.

Vertical GaN p-n Junction Diodes With High Breakdown Voltages Over 4 kV

Vertical structured GaN power devices have recently been attracting a great interest because of their potential on extremely high-power conversion efficiency. This letter describes increased breakdown voltages in the vertical GaN p-n diodes fabricated on the free-standing GaN substrates. By applying multiple lightly Si doped n-GaN drift layers to the p-n diode, the record breakdown voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) of 4.7 kV combined with low specific differential ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) of 1.7 mΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were achieved. With reducing the Si-doping concentration of the top n-GaN drift layer adjacent to the p-n junction using well-controlled metal-organic vapor phase epitaxy systems, the peak electric field at the p-n junction could be suppressed under high negatively biased conditions. The second drift layer with a moderate doping concentration contributed to the low R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . A Baliga's figure of merit (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) was 13 GW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . These are the best values ever reported among those achieved by GaN p-n junction diodes on the free-standing GaN substrates.

4-kV and 2.8-$\text{m}\Omega $ -cm2 Vertical GaN p-n Diodes With Low Leakage Currents

There is great interest in bulk GaN-based power electronics devices for applications requiring breakdown voltages greater than 3.3 kV. In this letter, the vertical GaN p-n diodes fabricated on improved bulk GaN substrates demonstrating low leakage currents ( $10^{4}$ cm $^{-2}$ ) bulk GaN substrates with improved quality and specifications that are uniquely suitable for power electronic device applications. The measured devices show breakdown voltages larger than 4 kV with an area differential specific ON-resistance ( $R_{\textrm {sp}}$ ) of less than 3 $\text{m}\Omega $ -cm2. Applications that would require such breakdown voltages, include ship propulsion, rail, wind, uninterruptable power supplies, and the power grid.

Temperature dependence of forward characteristics for ultrahigh-voltage SiC p–i–n diodes with a long carrier lifetime

Forward characteristics of ultrahigh-voltage 4H-SiC p–i–n diodes having four different n−-layer (i-layer) thicknesses from 48 to 198 µm were investigated in the temperature range from room temperature to 573 K. After enhancement of carrier lifetimes in i-layers, nearly ideal forward characteristics (differential on-resistance = 1.1–5.5 mΩ cm2 at 100 A/cm2) were obtained at room temperature. The forward voltage drop decreased with temperature, which is consistent with the temperature dependence of junction voltage. The differential on-resistance exhibited a slight increase at elevated temperatures, which can mainly be ascribed to the increase in substrate resistance.

Reliability studies of vertical GaN devices based on bulk GaN substrates

There is great interest in wide band-gap semiconductor devices and most recently in vertical GaN structures for power electronic applications. In this paper initial reliability studies of vertical p–n diodes and vertical junction field effect transistors fabricated on pseudo bulk low defect density (104 to 106cm−2) GaN substrates are discussed. Homoepitaxial MOCVD growth of GaN on its native substrate and being able to control the doping in the drift layers in GaN has allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40μm and net carrier electron concentrations of 2×1015 to 2×1016cm−3. This parameter range is suitable for applications requiring breakdown voltages of 1200V to 5kV with a proper edge termination strategy. Measured devices demonstrate power device figure of merit of differential specific on-resistance (Rsp) of 2.8mΩ-cm2 for a breakdown voltage of 4.1kV. The improvement in the substrate quality over the last few years has resulted in the fabrication of diodes with areas as large as 16mm2, with breakdown voltages exceeding 1200V, and pulsed (100μs) currents of 100–400A. Furthermore, impact ionization based avalanche breakdown has been demonstrated in GaN for the first time due to the high quality of the crystals grown on the native substrates. With these key demonstrations firmly in place, it is necessary to evaluate the reliability performance of vertical GaN devices on bulk GaN substrates. The results of high temperature reverse bias (HTRB), high temperature operating life (HTOL), temperature humidity bias (THB), temperature cycling (TC), and inductive avalanche ruggedness tests conducted on vertical GaN devices packaged in standard power packages are reported. It is observed that fundamental failure mechanisms are almost always traced back to the starting substrate material quality, substrate miscut angle, and surface morphology post epi growth. No observation of Rds drift is made for vertical diodes or transistors fabricated on bulk GaN substrates under the stress conditions mentioned above once a suitable back metal and die attach process is developed.

Ultrahigh-Voltage SiC p-i-n Diodes With Improved Forward Characteristics

Silicon carbide (SiC) p-i-n diodes having five different n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -layer (i-layer) thicknesses from 48 to 268 μm are fabricated. The forward characteristics of SiC p-i-n diodes are significantly improved by carrier-lifetime enhancement. After this improvement, the differential on-resistance is inversely proportional to the square root of current density for all the diodes with different thicknesses of n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -layer. As a result, the forward current density-voltage characteristics can be approximately expressed by a parabolic function, as in the case of Si p-i-n diodes. Using a 268-μm-thick n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -layer, the lifetime enhancement, and an improved space-modulated junction termination extension structure, a very high blocking voltage over 26.9 kV and low differential on-resistance of 9.7 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are achieved.

Development of Ultrahigh-Voltage SiC Devices

Ultrahigh-voltage silicon carbide (SiC) devices [p-i-n diodes and insulated-gate bipolar transistors (IGBTs)] and switching test have been investigated. As a result, we have succeeded in developing a 13-kV p-i-n diode, 15-kV p-channel IGBT, and 16-kV flip-type n-channel implantation and epitaxial IGBT with a low differential specific on-resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\rm diff,on}$ </tex-math></inline-formula> ). It was revealed that a power module fabricated using a nanotech resin, Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ceramic substrate, and W base plate was suitable for ultrahigh voltage and high temperature. A switching test was carried out using a clamped inductive load circuit, which indicated that the energy loss of a circuit with ultrahigh-voltage SiC devices is lower than that of Si devices.

Vertical Power p-n Diodes Based on Bulk GaN

There is a great interest in wide-bandgap semiconductor devices and most recently in monolithic GaN structures for power electronics applications. In this paper, vertical p-n diodes fabricated on pseudobulk low defect density (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) GaN substrates are discussed. Homoepitaxial low-pressure metal organic chemical vapor deposition growth of GaN on its native substrate and being able to control and balance the n-type Si doping with background C impurity has allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> to 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . This parameter range is suitable for applications requiring breakdown voltages (BVs) of 600 V-4 kV with a proper edge termination strategy. Measured devices demonstrate near power device figure of merit, that is, differential specific on-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sp</sub> ) of 2 mΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for a BV of 2.6 kV and 2.95 mΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for a 3.7-kV device, respectively. The improvement in the substrate quality over the last few years has resulted in the fabrication of diodes with areas as large as 16 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with BVs exceeding 700 V and pulsed (100 μs) currents of 400 A. The structures fabricated are utilized to study in detail the temperature dependency of I-V characteristics, impact ionization and avalanche characteristics, and extract (estimate) modeling parameters such as electron mobility in the GaN c-direction (vertical) and hole minority carrier lifetimes. Some insight into device reliability is also provided.