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The effect of doping in the drift layer and the thickness and extent of extension beyond the cathode contact of a NiO bilayer in vertical NiO/β-Ga2O3 rectifiers is reported. Decreasing the drift layer doping from 8 × 1015 to 6.7 × 1015 cm−3 produced an increase in reverse breakdown voltage (VB) from 7.7 to 8.9 kV, the highest reported to date for small diameter devices (100 μm). Increasing the bottom NiO layer from 10 to 20 nm did not affect the forward current–voltage characteristics but did reduce reverse leakage current for wider guard rings and reduced the reverse recovery switching time. The NiO extension beyond the cathode metal to form guard rings had only a slight effect (∼5%) in reverse breakdown voltage. The use of NiO to form a pn heterojunction made a huge improvement in VB compared to conventional Schottky rectifiers, where the breakdown voltage was ∼1 kV. The on-state resistance (RON) was increased from 7.1 m Ω cm2 in Schottky rectifiers fabricated on the same wafer to 7.9 m Ω cm2 in heterojunctions. The maximum power figure of merit (VB)2/RON was 10.2 GW cm−2 for the 100 μm NiO/Ga2O3 devices. We also fabricated large area (1 mm2) devices on the same wafer, achieving VB of 4 kV and 4.1 A forward current. The figure-of-merit was 9 GW  cm−2 for thesemore »devices. These parameters are the highest reported for large area Ga2O3 rectifiers. Both the small area and large area devices have performance exceeding the unipolar power device performance of both SiC and GaN.« less

In this work, we demonstrate the rejuvenation of Ti/4H-SiC Schottky barrier diodes after forward current-induced degradation, at room temperature and in a few seconds, by exploiting the physics of high-energy electron interactions with defects. The diodes were intentionally degraded to a 42% decrease in forward current and a 9% increase in leakage current through accelerated electrical stressing. The key feature of our proposed rejuvenation process is very high current density electrical pulsing with low frequency and duty cycle to suppress any temperature rise. The primary stimulus is, therefore, the electron wind force, which is derived from the loss of the momentum of the high energy electrons upon collision with the defects. Such defect-specific or “just in location” mobilization of atoms allows a significant decrease in defect concentration, which is not possible with conventional thermal annealing that requires higher temperatures and longer times. We show evidence of rejuvenation with additional improvement in leakage current (16%) and forward current (38%) beyond the pristine condition. Transmission electron microscopy, geometric phase analysis, Raman spectroscopy, and energy dispersive x-ray-spectroscopy reveal the enhancement of defects and interfaces. The ultrafast and room temperature process has the potential for rejuvenating electronic devices operating in high power and harshmore »environmental conditions.« less

Vertical geometry NiO/β n-Ga2O/n+ Ga2O3 heterojunction rectifiers with contact sizes from 50 to 200 μm diameter showed breakdown voltages (VB) up to 7.5 kV for drift region carrier concentration of 8 × 1015 cm−3. This exceeds the unipolar 1D limit for SiC and was achieved without substrate thinning or annealing of the epi layer structure. The power figure-of-merit, VB2/RON, was 6.2 GW cm−2, where RON is the on-state resistance (9.3–14.7 mΩ cm2). The average electric field strength was 7.56 MV/cm, approaching the maximum for β-Ga2O3. The on–off ratio switching from 5 to 0 V was 2 × 1013, while it was 3 × 1010–2 × 1011 switching to 100 V. The turn-on voltage was in the range 1.9–2.1 V for the different contact diameters, while the reverse current density was in the range 2 × 10−8–2 × 10−9 A cm−2 at −100 V. The reverse recovery time was 21 ns, while the forward current density was >100 A/cm2 at 5 V.

There are numerous applications for deep UV AlGaN Light-Emitting Diodes (LEDs) in virus inactivation, air and water purification, sterilization, bioagent detection and UV polymer curing. The long-term stability of these LEDs is also of interest for long-duration space missions such as the Laser Interferometer Space Antenna (LISA), the first gravitational wave detector in space. We review the literature on long-term aging of these devices as a function of drive current, temperature and dc versus pulsed operation. The LEDs typically show a gradual decline in output power (up to 50%) over extended operating times (>100 h) and the rate of decline is mainly driven by current and temperature. Experimentally, the degradation rate is dependent on the cube of drive current density and exponentially on temperature. The main mechanism for this decline appears to be creation/migration of point defects. Pre-screening by considering the ratio of band edge-to-midgap emission and LED ideality factor is effective in identifying populations of devices that show long lifetimes (>10,000 h), defined as output power falling to 70% of the initial value.

The energy and beam current dependence of Ga⁺focused ion beam milling damage on the sidewall of vertical rectifiers fabricated on n-type Ga₂O₃was investigated with 5–30 kV ions and beam currents from 1.3–20 nA. The sidewall damage was introduced by etching a mesa along one edge of existing Ga₂O₃rectifiers. We employed on-state resistance, forward and reverse leakage current, Schottky barrier height, and diode ideality factor from the vertical rectifiers as potential measures of the extent of the ion-induced sidewall damage. Rectifiers of different diameters were exposed to the ion beams and the “zero-area” parameters extracted by extrapolating to zero area and normalizing for milling depth. Forward currents degraded with exposure to any of our beam conductions, while reverse current was unaffected. On-state resistance was found to be most sensitive of the device parameters to Ga⁺beam energy and current. Beam current was the most important parameter in creating sidewall damage. Use of subsequent lower beam energies and currents after an initial 30 kV mill sequence was able to reduce residual damage effects but not to the point of initial lower beam current exposures.

In this study, the response to a heavy-ion strike and the resulting single effect burnout on beta-Ga 2 O 3 Schottky diodes with biased field rings is investigated via TCAD. The model used to simulate the device under high-reverse bias is validated using experimental current-voltage (I-V) curves. A field ring configuration for the device demonstrates an improved charge removal after simulated heavy-ion strikes. If the time scale for charge removal is faster than single event burnout, this can be an effective mechanism for reducing the effect of single ion strikes. This study explores various configurations of the termination structure and shows the impact of different design parameters in terms of a transient response after the ion strike.

While radiation is known to degrade AlGaN/GaN high-electron-mobility transistors (HEMTs), the question remains on the extent of damage governed by the presence of an electrical field in the device. In this study, we induced displacement damage in HEMTs in both ON and OFF states by irradiating with 2.8 MeV Au⁴⁺ion to fluence levels ranging from$1.72\times {10}^{10}$to$3.745\times {10}^{13}$ions cm⁻², or 0.001–2 displacement per atom (dpa). Electrical measurement is donein situ, and high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray (EDX), geometrical phase analysis (GPA), and micro-Raman are performed on the highest fluence of Au⁴⁺irradiated devices. The selected heavy ion irradiation causes cascade damage in the passivation, AlGaN, and GaN layers and at all associated interfaces. After just 0.1 dpa, the current density in the ON-mode device deteriorates by two orders of magnitude, whereas the OFF-mode device totally ceases to operate. Moreover, six orders of magnitude increase in leakage current and loss of gate control over the 2-dimensional electron gas channel are observed. GPA and Raman analysis reveal strain relaxation after a 2 dpa damage level in devices. Significant defects and intermixing of atoms near AlGaN/GaN interfaces and GaN layer are found from HRTEM and EDX analyses,more »which can substantially alter device characteristics and result in complete failure.

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NiO/β-(Al x Ga 1− x ) 2 O 3 /Ga 2 O 3 heterojunction lateral geometry rectifiers with diameter 50–100  μm exhibited maximum reverse breakdown voltages >7 kV, showing the advantage of increasing the bandgap using the β-(Al x Ga 1− x ) 2 O 3 alloy. This Si-doped alloy layer was grown by metal organic chemical vapor deposition with an Al composition of ∼21%. On-state resistances were in the range of 50–2180 Ω cm 2 , leading to power figures-of-merit up to 0.72 MW cm −2 . The forward turn-on voltage was in the range of 2.3–2.5 V, with maximum on/off ratios >700 when switching from 5 V forward to reverse biases up to −100 V. Transmission line measurements showed the specific contact resistance was 0.12 Ω cm 2 . The breakdown voltage is among the highest reported for any lateral geometry Ga 2 O 3 -based rectifier.

There is increasing interest in α-polytype Ga 2 O 3 for power device applications, but there are few published reports on dielectrics for this material. Finding a dielectric with large band offsets for both valence and conduction bands is especially challenging given its large bandgap of 5.1 eV. One option is HfSiO 4 deposited by atomic layer deposition (ALD), which provides conformal, low damage deposition and has a bandgap of 7 eV. The valence band offset of the HfSiO 4 /Ga 2 O 3 heterointerface was measured using x-ray photoelectron spectroscopy. The single-crystal α-Ga 2 O 3 was grown by halide vapor phase epitaxy on sapphire substrates. The valence band offset was 0.82 ± 0.20 eV (staggered gap, type-II alignment) for ALD HfSiO 4 on α-Ga 0.2 O 3 . The corresponding conduction band offset was −2.72 ± 0.45 eV, providing no barrier to electrons moving into Ga 2 O 3 .

The temperature-dependent behavior of on/off ratio and reverse recovery time in vertical heterojunction p-NiO/β n-Ga 2 O/n + Ga 2 O 3 rectifiers was investigated over the temperature range of 25–300 °C. The device characteristics in forward bias showed evidence of multiple current transport mechanisms and were found to be dependent on the applied bias voltages and temperatures. The on–off ratio decreased from 3 × 10 6 at 25 °C to 2.5 × 10 4 at 300 °C for switching to 100 V reverse bias. For 200  μm diameter rectifiers, the reverse recovery time of ∼21 ns was independent of temperature, with the I rr monotonically increasing from 15.1 mA at 25 °C to 25.6 mA at 250 °C and dropping at 300 °C. The dI/dt increased from 4.2 to 4.6 A/ μs over this temperature range. The turn-on voltage decreased from 2.9 V at 25 °C to 1.7 V at 300 °C. The temperature coefficient of breakdown voltage was negative and does not support the presence of avalanche breakdown in NiO/β-Ga 2 O 3 rectifiers. The energy loss during switching from 100 V was in the range 23–31  μJ over the temperature range investigated.