AlGaN/GaN high-electron-mobility transistors (HEMTs) are crucial components in high-frequency and high-power electronic applications. However, their surfaces and interfaces inherently contain dangling bonds and contaminants resulting from chemisorbed impurities. Additionally, fabrication processes such as mesa etching and via formation introduce plasma-induced defects, which can substantially degrade device performance. Therefore, understanding surface passivation mechanisms and techniques is essential to mitigate surface state effects and maximize device efficiency. In this review, we examine recent advances in surface passivation of GaN-based HEMTs. We analyze the surface characteristics of plasma-etched (Al)GaN layers subjected to various treatments, including chemical solutions, ion implantation, and plasma processes. Furthermore, we discuss the impact of different passivation dielectric materials (e.g. SixNy, Al2O3, HfO2, SiO2, etc.) on the electrical performance of HEMTs. This review aims to identify effective passivation strategies to enhance the overall efficiency and reliability of AlGaN/GaN HEMTs.
Gallium oxide (Ga2O3) has emerged as a promising ultra-wide-bandgap semiconductor for extreme-temperature electronics operating beyond the thermal limits of conventional devices. Its wide bandgap of 4.7–5.3 eV results in an exceptionally low intrinsic carrier concentration (∼10-26 cm-3) and a high critical electric field (∼8 MV/cm), enabling low leakage current, high breakdown strength, and stable operation at elevated temperatures. This review comprehensively examines Ga2O3 Schottky barrier diodes (SBDs) for high-temperature power and optoelectronic applications, with emphasis on temperature-dependent material properties and critical device parameters, including Schottky barrier height, leakage current, and breakdown voltage. Comparison with GaN indicates that, although Ga2O3 SBDs possess superior intrinsic material properties, the practical development of power devices remains constrained by low thermal conductivity, Schottky-interface instability, premature breakdown, and limited long-term reliability under high electric fields and current densities. In contrast, Ga2O3 SBDs have demonstrated exceptional performance as solar-blind ultraviolet (200–280 nm) and X-ray (1–20 keV) detectors, maintaining photosensitivity above 105 μC·Gy-1·cm-2 and photo-to-dark current ratios above 102 at 573 K without active cooling. This difference arises because Ga2O3 power devices require high-quality substrates, robust interfaces, effective thermal management, and high-voltage packaging, resulting in greater fabrication complexity and cost. In contrast, optoelectronic devices exploit the intrinsically low carrier concentration and wide-bandgap absorption of Ga2O3 at low or moderate bias and can be fabricated as thin films on relatively low-cost sapphire substrates. These advantages have allowed Ga2O3 optoelectronic devices to progress more rapidly toward practical deployment, whereas power-device applications remain constrained by reliability, thermal management, and manufacturing cost.
Infrared detection technology has become indispensable across defense, industrial monitoring, and civilian imaging systems. In recent years, the development of high operating temperature (HOT) infrared detectors has emerged as a major research focus, driven by the demand for reduced size, weight, power, and cost (SWaP-C) through diminished reliance on cryogenic cooling. To enable efficient HOT operation, extensive efforts have been devoted to various material systems, including HgCdTe, quantum wells, and emerging antimonide-based semiconductors. Among these candidates, antimonide-based materials have attracted significant attention owing to their exceptional band-structure engineering flexibility, high carrier mobility, long carrier lifetime, and low Auger recombination rate. Within the antimonide semiconductor platform, substantial advances in dark-current suppression and noise reduction have been achieved in both InAsSb alloy photodetectors and Type-II superlattice (T2SL) devices, highlighting the considerable promise of antimonide infrared detectors for HOT operation. The concurrent advancement of these approaches highlights the growing prominence of antimonide platforms for next-generation HOT infrared detection technologies. In this review, we provide a comprehensive overview of recent progress in Sb-based HOT infrared detectors, focusing on the underlying device physics and performance enhancement strategies. Current challenges in epitaxial material growth, device engineering, and system integration are discussed, together with future directions toward HOT and large-format focal plane arrays toward next-generation infrared detection technologies.
Electrochemical reduction reactions connect renewable electricity with hydrogen, carbon products, and ammonia-related chemistry, but catalyst design remains difficult because activity, selectivity, and durability require different binding strengths and because active surfaces can reconstruct under bias. High-entropy alloys (HEAs) and related multi-principal-element catalysts address this challenge by providing statistical populations of surface motifs rather than a single averaged active site. This Review discusses HEA and HEA-derived electrocatalysts for the hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), and nitrate reduction reaction (NO3RR), with emphasis on synthesis, theory, operando characterization, benchmarking, and data-driven discovery. Three conclusions emerge. First, HEA design should be expressed in terms of motif probabilities, adsorption-energy distributions, and near-optimal site fractions, because rare local environments can control macroscopic activity and selectivity. Second, catalyst architecture and active-state chemistry must be considered together: synthesis route, phase purity, porosity, compositional gradients, and operando segregation determine the motif distribution sampled during reaction. Third, rigorous benchmarking is essential. Matched low-entropy controls, surface-sensitive composition analysis, per-site activity metrics, and dissolution-aware durability tests are needed to distinguish entropy-enabled effects from conventional alloying or reconstruction. We conclude with design rules and a reporting checklist covering composition verification, operando site mapping, stability analysis, and nitrogen accounting. These practices can help convert chemical disorder in HEAs into reproducible design principles for multi-site electrocatalysis.
