In this paper, the authors describe the effectiveness of thermal annealing in vacuum for quantum efficiency (QE) recovery from Cs/O-activated GaN and GaAs photocathodes. The QE of Cs/O-activated GaN photocathodes at 3.4 eV dropped from 1.0% to <0.001% upon exposure to nitrogen and then increased to 0.6% upon annealing. On the other hand, the QE of Cs/O-activated GaAs at 1.42 eV did not increase after annealing. In addition, after Cs/O activation, the sample was exposed to normal laboratory air and installed in an X-ray photoemission spectroscopy system. Upon annealing at 330 °C, three key results were confirmed as follows: (1) the work function decreased by 0.32 eV, (2) the chemical states of Cs 4d and Ga 3d were unchanged, and (3) the intensities of O 1s and C 1s on the high-binding-energy side decreased. In conclusion, the experimental results indicate that the annealing recovers the QE of Cs/O-activated GaN photocathode.
As the size of micro light-emitting diodes (μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power (Pbias) on the performance of μLEDs and found that the current–voltage and light output–current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays.
Fuel of UO/sub 2/ containing a high content of gadolinia is planned to be used in pressurized water reactor high-burnup fuels. The UO/sub 2/-Gd/sub 2/O/sub 3/ fuel is in the state of solid solution in which a part of the uranium atoms in UO/sub 2/ are substituted by gadolinium atoms. The oxygen-to-metal (O/M) ratio of the solid solution is one of the most important factors affecting fuel properties and irradiation performance. The M represents metals of uranium and gadolinium. The oxygen-to-uranium O/U ratio of UO/sub 2/ fuel is usually measured by gravimetric analysis during oxidation of UO/sub 2/ to U/sub 3/O/sub 8/. In contrast with UO/sub 2/, it is difficult to measure the O/M ratio of (U,Gd)O/sub 2/ solid solution by gravimetry, because it is not clear whether the oxidation product of the solid solution is U/sub 3/O/sub 8/-Gd/sub 2/O/sub 3/ mixture, (U,Gd)/sub 3/O/sub 8/, or others. In this study, the measuring method of the O/M ratio of the solid solution by gravimetry has been developed and evaluated by examining oxidation behavior and oxidation products of the solid solution.
In this review, the epitaxial growth of transition metal nitrides (TMNs) is explored, focusing on sputter epitaxy as a versatile method for developing advanced materials such as NbN superconductors and ScAlN ferroelectrics. In the recent studies, it is shown that, unlike conventional growth techniques, sputter epitaxy enables the deposition of high‐melting‐point transition metals, offering advantages for growing thin films with unique properties. In this review, recent progress in integrating TMNs with nitride semiconductors to fabricate hybrid devices that exhibit both superconducting and ferroelectric characteristics is addressed. These developments underscore the potential of sputter epitaxy as a foundational tool for advancing the next generation of electronic and quantum devices.
