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  1. Free, publicly-accessible full text available August 1, 2024
  2. 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. 
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    Free, publicly-accessible full text available May 15, 2024
  3. Abstract

    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 from1.72×1010to3.745×1013ions 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, which can substantially alter device characteristics and result in complete failure.

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  4. Free, publicly-accessible full text available February 1, 2024
  5. Abstract Discovering multifunctional materials with tunable plasmonic properties, capable of surviving harsh environments is critical for advanced optical and telecommunication applications. We chose high-entropy transition-metal carbides because of their exceptional thermal, chemical stability, and mechanical properties. By integrating computational thermodynamic disorder modeling and time-dependent density functional theory characterization, we discovered a crossover energy in the infrared and visible range, corresponding to a metal-to-dielectric transition, exploitable for plasmonics. It was also found that the optical response of high-entropy carbides can be largely tuned from the near-IR to visible when changing the transition metal components and their concentration. By monitoring the electronic structures, we suggest rules for optimizing optical properties and designing tailored high-entropy ceramics. Experiments performed on the archetype carbide HfTa 4 C 5 yielded plasmonic properties from room temperature to 1500K. Here we propose plasmonic transition-metal high-entropy carbides as a class of multifunctional materials. Their combination of plasmonic activity, high-hardness, and extraordinary thermal stability will result in yet unexplored applications. 
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    Free, publicly-accessible full text available December 1, 2023
  6. Strain localization in microelectronic devices commonly arises from device geometry, materials, and fabrication processing. In this study, we controllably relieve the local strain field of AlGaN/GaN HEMTs by milling micro-trenches underneath the channel and compare the device performance as a function of the relieved strain as well as radiation dosage. Micro-Raman results suggest that the trenches locally relax the strain in device layers, decreasing the 2DEG density and mobility. Intriguingly, such strain relaxation is shown to minimize the radiation damage, measured after 10 Mrads of 60Co-gamma exposure. For example, a 6-trench device showed only ∼8% and ∼6% decrease in saturation drain current and maximum transconductance, respectively, compared to corresponding values of ∼15% and ∼30% in a no-trench device. Negative and positive threshold voltage shifts are observed in 6-trench and no-trench devices, respectively, after gamma radiation. We hypothesize that the extent of gamma radiation damage depends on the strain level in the devices. Thus, even though milling a trench decreases 2DEG mobility, such decrease under gamma radiation is far less in a 6-trench device (∼1.5%) compared to a no-trench device (∼20%) with higher built-in strain.

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  7. Radiation damage in electronic devices is known to be influenced by physics, design, and materials system. Here, we report the effects of biasing state (such as ON and OFF) and pre-existing damage in GaN high electron mobility transistors exposed to γ radiation. Controlled and accelerated DC biasing was used to prestress the devices, which showed significant degradation in device characteristics compared to pristine devices under ON and OFF states after γ irradiation. The experiment is performed in situ for the ON-state to investigate transient effects during irradiation until the total dose reaches 10 Mrad. It shows that threshold voltage, maximum transconductance, and leakage current initially decrease with dosage but slowly converge to a steady value at higher doses. After 10 Mrad irradiation, the OFF-state device demonstrates larger RON and one order of magnitude increased leakage current compared to the ON-state irradiated device. The micro-Raman study also confirms that the ON-state operation shows more radiation hardness than OFF and prestressed devices. Prestressed devices generate the highest threshold voltage shift from −2.85 to −2.49 V and two orders of magnitude higher leakage current with decreased saturation current after irradiation. These findings indicate that high electric fields during stressing can generate defects by modifying strain distribution, and higher defect density can not only create more charges during irradiation but also accelerate the diffusion process from the ionizing track to the nearest collector and consequently degrade device performances.

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  8. NiO/Ga2O3 heterojunction rectifiers were exposed to 1 Mrad fluences of Co-60 γ-rays either with or without reverse biases. While there is a small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000× reduction in forward current and a 100× increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on–off ratio is also reduced by almost five orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of <4 cm−1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current–voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate that these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

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  9. As electronic systems become larger and more complex, detection of the most vulnerable regions (MVR) to radiation exposure becomes more difficult and time consuming. We present a heuristic approach where the mechanical and thermal aspects of devices are exploited to quickly identify MVRs. Our approach involves the topological mapping of two device conditions. The first condition identifies regions with the highest mechanical strain or density of defects and interfaces via thermal wave probing and phase analysis. The second condition identifies regions with high electrical field. It is hypothesized that the region with the highest thermal wave penetration resistance and electrical field will exhibit the highest sensitivity to incoming radiation for single events and potentially, total ionizing dose. Our approach implements a simplistic design that improves analysis time by ∼2–3 orders of magnitude over current radiation sensitivity mapping methods. The design is demonstrated on the well-studied operational amplifier LM124, which shows agreement with the literature in identifying sensitive transistors–QR1, Q9, and Q18–with relatively high phase percentile values (>70%) and ΔT percentiles (>50%), satisfying conditions for elevated radiation susceptibility. This is followed by experimental results on a static random access memory (HM-6504) and a Xilinx Artix-7 35 T system on a chip. 
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