Hafijur Rahman

Ultra-wide-bandgap (UWBG) semiconductors are promising for power electronics, but high-breakdown diodes often suffer from high turn-on voltages and defect-related performance limits, requiring high-temperature processing. This work demonstrates that electron wind force (EWF)-assisted processing significantly reduces the turn-on voltage of aluminum nitride (AlN) diodes at room temperature, eliminating the need for thermal annealing. Across four room-temperature devices, the average turn-on voltage decreases from 2.34 ± 0.23 to 1.23 ± 0.38 V after EWF processing, while the forward current at 5 V increases from 78.23 ± 20.75 pA to 110.4 ± 20.8 pA. Infrared thermal imaging during processing shows that the sample temperature remains close to ambient, supporting the low-thermal-budget nature of the approach. High-frequency capacitance–voltage measurements reveal a systematic modification of junction electrostatics, indicating reorganization of electrically active defect states within the depletion region rather than changes in bulk conductivity. Complementary Raman spectroscopy shows a modest narrowing of the E ₂ (high) phonon linewidth, from 5.04 to 4.82 cm ^-1 , reflecting reduced defect-related phonon scattering. Time-dependent measurements show partial relaxation of the turn-on voltage shift after four days, suggesting that the EWF-induced modification is metastable rather than conventional bulk lattice annealing. Together, these results show that room-temperature EWF processing provides an electrically driven route to lowering the turn-on voltage of AlN diodes, addressing a key limitation in UWBG rectifiers.

Annealing of electronic devices is performed at elevated temperatures since conventional wisdom suggests that only thermal energy can mobilize and annihilate the defects that are grown in the semiconductor or induced by device processing steps. To demonstrate that elevated temperature is not a prerequisite for annealing, commercially available 1700 V silicon carbide MOSFETs were first intentionally degraded using Co-60 gamma irradiation to a total dose of 1 Mrad(Si). A direct current was then applied to induce an electron wind force—a mechanical stimulus arising from the transfer of electron momentum to lattice defects. Throughout the treatment, the device junction temperature was maintained at ∼20 °C by actively cooling the chamber to −35 °C using nitrogen gas flow. Post-irradiation transfer, output, capacitance–voltage, and drain-lag responses revealed dose-dependent negative threshold voltage shifts and enhanced drain current due to positive oxide charge buildup. Remarkably, the applied electron flux provided sufficient momentum to liberate trapped carriers and reconfigure metastable defects, enabling ∼98–100% recovery of threshold voltage, drain current, and capacitance across all irradiation doses. These findings indicate that high temperature may not be the only driving force for defect mitigation in conducting and semiconducting materials, thereby impacting the resilience of power electronics in aerospace and nuclear applications.

Resilience to ionizing radiation is crucial for electronic devices in space and nuclear applications. Traditionally, this is achieved through new design, materials, shielding, or redundancy strategies. In this study, we demonstrate a new approach: repeated rejuvenation using the Electron Wind Force (EWF). Commercially available SiC MOSFETs were irradiated with Co-60 gamma beam up to a cumulative dose of 10 Mrad. During the process, in situ EWF annealing was applied after every 2 Mrad increment. Key device characteristics such as output, transfer, and leakage were characterized in each irradiation-rejuvenation cycle. We observe an initial increase in drain current at lower doses, attributed to positive charge build-up by creation of interface traps. As the radiation dose accumulates, the non-annealed device experiences substantial degradation: drain current sharply declines, and gate leakage rises significantly. In contrast, the in situ EWF-annealed device repeatedly recovers its drain current following each irradiation step and preserves a near-pristine gate leakage profile. The EWF process takes place at room temperature, takes less than a minute and requires no special handling, making it a potential candidate for in-operando rejuvenation for unprecedented resilience in ionizing radiation environments.

Gamma radiation is detrimental to semiconductor-based sensors or instrumentation. The ensuing damage can be very difficult to repair with conventional annealing approaches, particularly in as-deployed conditions. This study proposes application of the non-thermal electron wind force (EWF) to restore device performance and thus improve resilience to radiation exposure. The technique is demonstrated on Zener diodes exposed to Co-60 gamma radiation doses up to 2.65 Mrad (Si), which resulted in significant degradation of forward and reverse bias currents due to the formation of radiation-induced defects. EWF annealing, conducted at near-ambient temperatures for just one minute, not only completely restored the forward current affected by 2.65 Mrad (Si) of gamma radiation but also enhanced it beyond the pristine condition. In terms of reverse bias, the treatment achieved a recovery of 74.5%. Raman spectroscopy revealed increased full width at half maximum values of the characteristic peak of phonon mode of crystalline Si following the EWF annealing, indicating healing of lattice disorder and defects. Thermal annealing at 100 °C for 90 min showed no recovery or even more degradation, probably due to additional thermal stress. Because EWF annealing requires only electrical connections, it can be implemented “in-operando,” extending lifetime of semiconductor devices in radiation environments.

Traditional defect recovery methods rely on high-temperature annealing, often exceeding 750 °C for FeCrAl. In this study, we introduce electron wind force (EWF)-assisted annealing as an alternative approach to mitigate irradiation-induced defects at significantly lower temperatures. FeCrAl samples irradiated with 5 MeV Zr²⁺ ions at a dose of 10¹⁴ cm⁻² were annealed using EWF at 250 °C for 60 s. We demonstrate a remarkable transformation in the irradiated microstructure, where significant increases in kernel average misorientation (KAM) and low-angle grain boundaries (LAGBs) typically indicate heightened defect density; the use of EWF annealing reversed these effects. X-ray diffraction (XRD) confirmed these findings, showing substantial reductions in full width at half maximum (FWHM) values and a realignment of peak positions toward their original states, indicative of stress and defect recovery. To compare the effectiveness of EWF, we also conducted traditional thermal annealing at 250 °C for 7 h, which proved less effective in defect recovery as evidenced by less pronounced improvements in XRD FWHM values.

Semiconductor devices contain defects and localized mechanical stress even in their pristine states, persisting after post-fabrication annealing. We hypothesize that these pre-existing conditions, with their lower threshold energy for defect proliferation and/or ionization, may serve as nuclei for radiation damage. To test this hypothesis, we adopted a two-pronged approach: (a) performing electron wind force (EWF) annealing preemptively on pristine Zener diodes to eliminate pre-existing defects before radiation exposure, and (b) applying EWF annealing restoratively on devices already damaged by radiation. The EWF process is non-thermal and can eliminate defects below 30 °C that persist through conventional thermal annealing. Both pristine and EWF-annealed pristine devices were exposed to 15 MeV protons with a fluence of 10¹⁴ cm⁻². Radiation damage increased the ideality factor from 1 to 2.33 in the pristine devices, while the preemptively EWF-annealed devices showed remarkable resilience, with an ideality factor of 1.5. Similar performance improvements were observed with restorative EWF annealing on radiation-damaged devices. This resilience and recovery in performance are further supported by Raman spectroscopy indicating enhanced crystallinity compared to the pristine condition. These findings demonstrate the potential of EWF annealing as both a protective and restorative treatment for semiconductor devices in high-radiation environments.

Lateral NiO/AIN heterojunction diodes (HJDs) with breakdown voltage up to 11.6 kV and Ni/Au/AlN Schottky barrier diodes (SBDs) with V_B of 8.6 kV were fabricated on layers grown on sapphire substrates by metalorganic chemical vapor phase deposition. The power figure-of-merits V_B ²/R_ON where R_ON is the on-resistance were 0.31 MW·cm⁻² for HJD and 0.16 MW·cm⁻² for SBD. The lowest turn-on voltages were ∼2.03 and 1.91 V for HJDs and SBDs, respectively, with ON/OFF ratios up to 10². The maximum field before breakdown was 0.45 MV·cm⁻¹ in HJDs and 0.31 MV·cm⁻¹ in SBDs. These correspond to −1. This work demonstrates there is still significant optimization to be done in the overall quality of the AlN, including purity, crystal perfection, and defect density to realize the potential of this material as an ultra-wide bandgap semiconductor for efficient multi-kV power switching applications. Our results also demonstrate the promise of NiO as a p-type conducting oxide for forming heterojunctions with AlN.

Polycrystalline graphite contains multi-scale defects, which are difficult to anneal thermally because of the extremely high temperatures involved in the manufacturing process. In this study, we demonstrate annealing of nuclear graphite NBG-18 at temperatures below 28 °C, exploiting the electron wind force, a non-thermal stimulus. High current density pulses were passed through the specimens with a very low-duty cycle so that the electron momentum could mobilize the defects without heating the specimen. The effectiveness of this technique is presented with a significant decrease in electrical resistivity, defect counts from X-ray computed tomography, Raman spectroscopy, and nanoindentation-based mechanical characterization. Such multi-modal evidence highlights the feasibility of nanoscale defect control at temperatures about two orders of magnitude below the graphitization temperature.

This study investigates the effectiveness of combined thermal and athermal stimuli in mitigating the extremely high-density nature of dislocation networks in the form of low-angle grain boundaries in FeCrAl alloy. Electron wind force, generated from very low duty cycle and high current density pulses, was used as the athermal stimulus. The electron wind force stimulus alone was unable to remove the residual stress (80% low-angle grain boundaries) due to cold rolling to 25% thickness reduction. When the duty cycle was increased to allow average temperature of 100 °C, the specimen could be effectively annealed in 1 min at a current density of 3300 A/mm². In comparison, conventional thermal annealing requires at least 750 °C and 1.5 h. For specimens with 50% thickness reduction (85% low-angle grain boundaries), the electron wind force was again unable to anneal the defects even at 3300 A/mm² current density and average temperature of 100 °C. Intriguingly, allowing average concurrent temperature of 200 °C eliminated almost all the low-angle grain boundaries at a current density of 700 A/mm², even lower than that required for the 25% thickness reduced specimens. Comprehensive electron and X-ray diffraction evidence show that alloys with extremely high defect density can be effectively annealed in less than a minute at approximately 200 °C, offering a substantial improvement over conventional high-temperature annealing.