This letter demonstrates vertical Ga ₂ O ₃ Schottky barrier diodes (SBDs) with a novel edge termination, the small-angle beveled field plate (SABFP), fabricated on thinned $\text{G}_{{2}}\text{O}_{{3}}$ substrates. Non-punch-though design is used for the drift region with a donor concentration of ${3}\sim {3.5} \times {10} ^{{16}}$ cm ⁻³ , rendering a device differential ON-resistance of $\sim 2~\text{m}\Omega ~\cdot $ cm ² . A new wet-etch technique is developed by using a bi-layer mask, which consists of spin-on-glass (SOG) and plasma-enhanced chemical vapor deposited (PECVD) SiO ₂ , to fabricate a very small bevel angle (∼ 1°) in the mesa and field plates. This SABFP structure facilitates the electric field spreading at device edges, rendering a breakdown voltage of 1100 V, a peak electric field of 3.5 MV/cm in Ga ₂ O ₃ at the Schottky contact edge, and an averaged electric field over 3.4 MV/cm underneath the contact. Our device demonstrates a Baliga’s figure of merit of 0.6 GW/cm ² , which is among the highest in all reported Ga ₂ O ₃ power devices and comparable to the state-of-the-art GaN SBDs. These results show the great potential of Ga ₂ O ₃ SBDs for future power applications.

An essential ruggedness of power devices is the capability of safely withstanding the surge energy. The surge ruggedness of the GaN high-electron-mobility transistor (HEMT), a power transistor with no or minimal avalanche capability, has not been fully understood. This article unveils the comprehensive physics associated with the surge-energy withstand process and the failure mechanisms of p-gate GaN HEMTs. Two commercial p-gate GaN HEMTs with Ohmic- and Schottky-type gate contacts are studied. Two circuits are developed to study the device surge ruggedness: an unclamped inductive switching circuit is first used to identify the withstand dynamics and failure mechanisms, and a clamped inductive switching circuit with a controllable parasitic inductance is then designed to mimic the surge energy in converter-like switching events. The p-gate GaN HEMT is found to withstand the surge energy through a resonant energy transfer between the device capacitance and the load/parasitic inductance rather than a resistive energy dissipation as occurred in the avalanche. If the device resonant voltage goes below zero, the device reversely turns on and the inductor is discharged. The device failure occurs at the transient of peak resonant voltage and is limited by the device overvoltage capability rather than the surge energy, dV/dt, or overvoltage duration. Almost no energy is dissipated in the resonant withstand process and the device failure is dominated by an electric field rather than a thermal runaway. These results provide critical understandings on the ruggedness of GaN HEMTs and important references for their qualifications and applications.

This work describes the high-temperature performance and avalanche capability of normally-off 1.2-K V-CLASS vertical gallium nitride (GaN) fin-channel junction field-effect transistors (Fin-JFETs). The GaN Fin-JFETs were fabricated by NexGen Power Systems, Inc. on 100-mm GaN-on-GaN wafers. The threshold voltage ( V _{\text TH} ) is over 2 V with less than 0.15 V shift from 25 °C to 200 °C. The specific ON-resistance ( R _{\scriptscriptstyle ON} ) increases from 0.82 at 25 °C to 1.8 \textmΩ·cm ² at 200 °C. The thermal stability of V _{\text TH} and R _{\scriptscriptstyle ON} are superior to the values reported in SiC MOSFETs and JFETs. At 200 °C, the gate leakage and drain leakage currents remain below 100 μ\textA at -7-V gate bias and 1200-V drain bias, respectively. The gate leakage current mechanism is consistent with carrier hopping across the lateral p-n junction. The high-bias drain leakage current can be well described by the Poole-Frenkel (PF) emission model. An avalanche breakdown voltage ( BV _{\text AVA} ) with positive temperature coefficient is shown in both the quasi-static I- V sweep and the unclamped inductive switching (UIS) tests. The UIS tests also reveal a BV _{\text AVA} over 1700 V and a critical avalanche energy ( E _{\text AVA} ) of 7.44 J/cm ² , with the E _{\text AVA} comparable to that of state-of-the-art SiC MOSFETs. These results show the great potentials of vertical GaN Fin-JFETs for medium-voltage power electronics applications.

This work demonstrates vertical Ga2O3 Schottky barrier diodes (SBDs) with a novel junction termination extension (JTE) comprising multiple layers of sputtered p-type nickel oxide (NiO). The NiO layers have the varied lengths to enable a graded decrease in effective charge density away from the main junction. The fabrication of this JTE obviates the etch or implantation and shows good throughput. The fabricated Ga2O3 SBDs exhibit a forward voltage below 1.9 V at the current density of 100 A/cm2, a differential specific on-resistance of 5.9 $\text{m}\Omega \cdot $ cm2, and a breakdown voltage over 2.5 kV. The Baliga’s figure of merit (FOM) exceeds 1 GW/cm2 and is among the highest in multi-kilovolt Ga2O3 SBDs. Besides, the capacitance of the JTE region is extracted, allowing for evaluation of the capacitance, charge, and switching FOM of 1.7 kV-class Ga2O3 SBDs with varied current ratings. The results show good promise of Ga2O3 SBDs for kilovolt power electronics.

Ultrawide-bandgap gallium oxide (Ga ₂ O ₃ ) devices have recently emerged as promising candidates for power electronics; however, the low thermal conductivity ( k _T ) of Ga ₂ O ₃ causes serious concerns about their electrothermal ruggedness. This letter presents the first experimental demonstrations of large-area Ga ₂ O ₃ Schottky barrier diodes (SBDs) packaged in the bottom-side-cooling and double-side-cooling configurations, and for the first time, characterizes the surge current capabilities of these packaged Ga ₂ O ₃ SBDs. Contrary to popular belief, Ga ₂ O ₃ SBDs with proper packaging show high surge current capabilities. The double-side-cooled Ga ₂ O ₃ SBDs with a 3 × 3-mm ² Schottky contact area can sustain a peak surge current over 60 A, with a ratio between the peak surge current and the rated current superior to that of similarly-rated commercial SiC SBDs. The key enabling mechanisms for this high surge current are the small temperature dependence of on -resistance, which strongly reduces the thermal runaway, and the double-side-cooled packaging, in which the heat is extracted directly from the Schottky junction and does not need to go through the low- k _T bulk Ga ₂ O ₃ chip. These results remove some crucial concerns regarding the electrothermal ruggedness of Ga ₂ O ₃ power devices and manifest the significance of their die-level thermal management.

This work demonstrates multi-channel AlGaN/GaN Schottky barrier diodes (SBDs) with a breakdown voltage (BV) over 10 kV, the highest BV reported in GaN devices to date. The epitaxial structure consists of a p-GaN cap layer and five AlGaN/GaN channels continuously grown on a low-cost 4-inch sapphire substrate. A novel device design is proposed for electric field management, i.e., the p-GaN reduced surface field (RESURF) structure, which balances the net charges in the multi-channel at reverse biases. The SBD with a 98- μm anode-to-cathode length ( L _AC ) shows a BV of 9.15 kV and a specific on-resistance ( R _{\scriptscriptstyle ON} ) of 29.5 mΩ·cm ² , rendering a Baliga's figure of merit (FOM) of 2.84 GW/cm ² . The SBD with a 123- μm L _AC shows a BV over 10 kV and a R _{\scriptscriptstyle ON} of 39 mΩ·cm ² , which is 2.5-fold lower than the R _{\scriptscriptstyle ON} of the state-of-the-art 10-kV SiC junction barrier Schottky diodes. The Baliga's FOMs of our 4.6-10 kV GaN SBDs well exceed the SiC unipolar limit. These results show the great promise of GaN for medium- and high-voltage power electronics.