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In this study, we explore the rejuvenation of a Zener diode degraded by high electrical stress, leading to a leftward shift, and broadening of the Zener breakdown voltage knee, alongside a 57% reduction in forward current. We employed a non-thermal annealing method involving high-density electric pulses with short pulse width and low frequency. The annealing process took <30 s at near-ambient temperature. Raman spectroscopy supports the electrical characterization, showing enhancement in crystallinity to explain the restoration of the breakdown knee followed by improvement in forward current by ∼85%.

 

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹²to 3.76 × 10¹⁴cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According toin-situRaman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

 

Thermal annealing is commonly used in fabrication processing and/or performance enhancement of electronic and opto-electronic devices. In this study, we investigate an alternative approach, where high current density pulses are used instead of high temperature. The basic premise is that the electron wind force, resulting from the momentum loss of high-energy electrons at defect sites, is capable of mobilizing internal defects. The proposed technique is demonstrated on commercially available optoelectronic devices with two different initial conditions. The first study involved a thermally degraded edge-emitting laser diode. About 90% of the resulting increase in forward current was mitigated by the proposed annealing technique where very low duty cycle was used to suppress any temperature rise. The second study was more challenging, where a pristine vertical-cavity surface-emitting laser (VCSEL) was subjected to similar processing to see if the technique can enhance performance. Encouragingly, this treatment yielded a notable improvement of over 20% in the forward current. These findings underscore the potential of electropulsing as an efficient in-operando technique for damage recovery and performance enhancement in optoelectronic devices.

 

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 these 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. 

NiO/β-Ga 2 O 3 vertical rectifiers exhibit near-temperature-independent breakdown voltages ( V B ) of >8 kV to 600 K. For 100 μm diameter devices, the power figure of merit ( V B ) 2 / R ON , where R ON is the on-state resistance, was 9.1 GW cm −2 at 300 K and 3.9 GW cm −2 at 600 K. By sharp contrast, Schottky rectifiers fabricated on the same wafers show V B of ∼1100 V at 300 K, with a negative temperature coefficient of breakdown of 2 V K −1 . The corresponding figures of merit for Schottky rectifiers were 0.22 GW cm −2 at 300 K and 0.59 MW cm −2 at 600 K. The on–off ratio remained >10 10 up to 600 K for heterojunction rectifiers but was 3 orders of magnitude lower over the entire temperature range for Schottky rectifiers. The power figure of merit is higher by a factor of approximately 6 than the 1-D unipolar limit of SiC. The reverse recovery times were ∼26 ± 2 ns for both types of devices and were independent of temperature. We also fabricated large area, 1 mm 2 rectifiers. These exhibited V B of 4 kV at 300 K and 3.6 kV at 600 K. The results show the promise of using this transparent oxide heterojunction for high temperature, high voltage applications. 

Large area (1 mm²) vertical NiO/βn-Ga₂O/n⁺Ga₂O₃heterojunction rectifiers are demonstrated with simultaneous high breakdown voltage and large conducting currents. The devices showed breakdown voltages (V_B) of 3.6 kV for a drift layer doping of 8 × 10¹⁵cm⁻³, with 4.8 A forward current. This performance is higher than the unipolar 1D limit for GaN, showing the promise ofβ-Ga₂O₃for future generations of high-power rectification devices. The breakdown voltage was a strong function of drift region carrier concentration, with V_Bdropping to 1.76 kV for epi layer doping of 2 × 10¹⁶cm⁻³. The power figure-of-merit, V_B²/R_ON, was 8.64 GW·cm⁻², where R_ONis the on-state resistance (1.5 mΩ cm²). The on-off ratio switching from 12 to 0 V was 2.8 × 10¹³, while it was 2 × 10¹²switching from 100 V. The turn-on voltage was 1.8 V. The reverse recovery time was 42 ns, with a reverse recovery current of 34 mA.

 

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. 

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 harsh environmental conditions. 

Neutrons generated through charge-exchange⁹Be (p; nⁱ)⁹Be reactions, with energies ranging from 0–33 MeV and an average energy of ∼9.8 MeV were used to irradiate conventional Schottky Ga₂O₃rectifiers and NiO/Ga₂O₃p-n heterojunction rectifiers to fluences of 1.1–2.2 × 10¹⁴cm⁻². The breakdown voltage was improved after irradiation for the Schottky rectifiers but was highly degraded for their NiO/Ga₂O₃counterparts. This may be a result of extended defect zones within the NiO. After irradiation, the switching characteristics were degraded and irradiated samples of both types could not survive switching above 0.7 A or 400 V, whereas reference samples were robust to 1 A and 1 kV. The carrier removal rate in both types of devices was ∼45 cm⁻¹. The forward currents and on-state resistances were only slightly degraded by neutron irradiation.