In this brief, a scaled In $_{{0}.{17}}$ Al $_{{0}.{83}}\text{N}$ /GaN high-electron-mobility transistor (HEMT) was fabricated on sapphire substrate with 47-nm ${T}$ -gate length, 300-nm source–drain distance, and selective area regrown $\text{n}^{+}$ -GaN. The device exhibits cutoff frequencies ${f}_{\text {T}}/{f}_{\text {max}}$ of 190/301 GHz, which gives a record sqrt ( ${f}_{\text {T}} \times {f}_{\text {max}}{)}$ = 239 GHz among reported Ga-polar GaN-on-sapphire HEMTs. The device shows a maximum current density, a peak external direct current transconductance, and an ${I}_{\text {on}}/{I}_{\text {off}}$ ratio of 1.45 A/mm, 610 mS/mm, and $2.9\times 10^{6}$ , respectively. Drain-induced barrier lowering of 75 mV/V is measured at ${I}_{\text {ds}}$ = 1 mA/mm between ${V}_{\text {ds}}$ = 1 V and 5 V. The three-terminal OFF-state breakdown voltage is 14.7 V. The effective electron velocity of the 2-D electron gas (2DEG) under the gate foot is estimated to be $1.4\times 10^{7}$ cm/s. These characteristics of this Ga-polar millimeter wave (mm-wave) GaN-on-sapphire HEMT are comparable with those state-of-the-art counterparts on SiC substrates.

A surface acoustic wave (SAW) resonator with quality factors ( Q ) of 3526/10205 at the resonant/anti-resonant frequencies ( f _r / f _a ) has been fabricated on thick MOCVD grown (0002) AlN films (4 μ m) on Sapphire. The impact of device parameters on Q of resonators, including aspect ratio of length to width ( L/W ), number of interdigital transducers, and IDT metal thickness, has been investigated. The high Q is obtained due to the large L/W value of 12 which can enhance the acoustic energy superimposition of interdigital transducers, and the thick AlN film (4 μ m), which can reduce the negative impact of seed layer. Moreover, temperature coefficient of frequency (TCF) values of -46.52/-46.09 ppm/°C for f _r / f _a with temperatures ranging from -50 °C to 250 °C and a high Q of 4027 at 250 °C of the resonator have been demonstrated for temperature sensor application.

The high-temperature operation of the AlGaN/GaN high electron mobility transistors (HEMTs) and direct-coupled FET logic (DCFL) inverters, NOR gates, and NAND gates are demonstrated. The ${p}$ -GaN-gate HEMTs which are used as drivers in DCFL circuits exhibit proper E-mode operation with a relatively stable threshold voltage ${V}_{\text {TH}}$ (drift −0.31 V) and high electron mobility $\mu $ of 587 cm2/ $\text{V}\cdot \text{S}$ at 300 °C. The fabricated logic gates have a small switching time at room temperature (RT). As the temperature increases to 300 °C, these logic gates exhibit a slight increase in switching time, wherein the fall time and rise time of the inverter from room temperature to 300 °C increases from 16 ns to 129 ns and 128 ns to $0.864~\mu \text{s}$ , respectively. The logic gates herein exhibit accurate and stable operation at 300 °C. Furthermore, the reason for the switching time increase at high temperature is revealed from the perspective of devices.

Strontium-90 (⁹⁰Sr) is the most abundant radionuclide in radioactive wastes, and is typically isolated by treatment with an inorganic ion-exchange material. Most inorganic ion-exchange materials contain oxygen. The ion-exchange chemistry of layered metal sulfides is relatively poorly explored compared with that of oxide ion-exchange materials. Here, a layered metal sulfide (UCR-28), constructed from [ZnGe₃S₉(H₂O)]⁴⁻ supertetrahedral clusters, was prepared under hydrothermal conditions and used for the removal of Sr²⁺ ions from aqueous solution. Batch experiments showed that UCR-28 had affinity for Sr²⁺ ions at pH values ranging from 1 to 10 and the maximum ion-exchange capacity of UCR-28 (50.1 mg/g) was achieved at pH 7. Thermodynamic parameters for the ion-exchange process were evaluated, and the enthalpy and Gibbs free energy results suggested the Sr²⁺ ion-exchange process was endothermic and spontaneous. The ion-exchange data were a good fit to the Langmuir model. In addition, the metal sulfide reported here had a relatively high thermal stability. The results of this study provide insight into the largely unknown ion-exchange chemistry of metal sulfides, and could be used for design of new chalcogenide frameworks with improved ion-exchange properties.

Schottky-gated terahertz high-electron mobility transistors with ultrathin barriers suffer from metal-induced gap states (MIGSs), leading to gate leakage and electron scattering that degrade transport properties. While oxygen plasma oxidation of the InAlN barrier can mitigate MIGS, it introduces defects and impurity scattering, further deteriorating channel performance. This study resolves this paradox by exploiting the thermodynamic oxidation selectivity between gallium nitride (GaN) and InAlN to selectively convert a GaN cap under the gate region into a wide-bandgap gallium oxynitride (GaON) layer, leaving the InAlN barrier intact. This barrier-friendly approach suppresses MIGS without sacrificing channel quality, achieving a near-theoretical intrinsic electron effective velocity (veff. i = 2.2 × 107 cm/s). The enhanced transport enables record RF performance: (fT/fmax = 240/530) GHz, a noise figure below 1 dB at Ka-band, attributed to suppressed interfacial scattering, and 8 dB linear gain at 94 GHz. With excellent uniformity, this GaON cap technology provides a scalable, reliable pathway to high-frequency GaN HEMTs that harmonize noise and power performance.

This work demonstrated a deep-ultraviolet (DUV) LED with an Al-graded p-AlGaN contact layer above the electron blocking layer to alleviate p-type contact resistance, the asymmetry of carriers transport, and the polarization effect. The fitting results from the ABC + f(n) model revealed that the LED has a higher radiative recombination coefficient than the conventional structures ever reported, which contributes to a lower carrier lifetime. The light output power of the LED at 350 mA is 44.71 mW, the peak external quantum efficiency (EQE) at 22.5 mA is 5.12%, the wall-plug efficiency at 9 mA is 4.40%. The 3 dB electrical-to-optical modulation bandwidth of the graded p-AlGaN contact layer LED is 390 MHz after impedance matching. In short, this study provides an in-depth analysis of the physical mechanism of the enhanced EQE and decreased carrier lifetime of DUV LEDs with Al-graded AlGaN as a p-type contact layer.