Search

A novel E-mode GaN high-electron-mobility field-effect transistor with a superlattice barrier doped with Mg by thermal diffusion. This strategy can provide new ideas for the commercialisation of E-mode devices.

Conventional silicon (Si)-based power devices face physical limitations—such as switching speed and energy efficiency—which can make it difficult to meet the increasing demand for high-power, low-loss, and fast-switching-frequency power devices in power electronic converter systems. Gallium nitride (GaN) is an excellent candidate for next-generation power devices, capable of improving the conversion efficiency of power systems owing to its wide band gap, high mobility, and high electric breakdown field. Apart from their cost effectiveness, GaN-based power high-electron-mobility transistors (HEMTs) on Si substrates exhibit excellent properties—such as low ON-resistance and fast switching—and are used primarily in power electronic applications in the fields of consumer electronics, new energy vehicles, and rail transit, amongst others. During the past decade, GaN-on-Si power HEMTs have made major breakthroughs in the development of GaN-based materials and device fabrication. However, the fabrication of GaN-based HEMTs on Si substrates faces various problems—for example, large lattice and thermal mismatches, as well as ‘melt-back etching’ at high temperatures between GaN and Si, and buffer/surface trapping induced leakage current and current collapse. These problems can lead to difficulties in both material growth and device fabrication. In this review, we focused on the current status and progress of GaN-on-Si power HEMTs in terms of both materials and devices. For the materials, we discuss the epitaxial growth of both a complete multilayer HEMT structure, and each functional layer of a HEMT structure on a Si substrate. For the devices, breakthroughs in critical fabrication technology and the related performances of GaN-based power HEMTs are discussed, and the latest development in GaN-based HEMTs are summarised. Based on recent progress, we speculate on the prospects for further development of GaN-based power HEMTs on Si. This review provides a comprehensive understanding of GaN-based HEMTs on Si, aiming to highlight its development in the fields of microelectronics and integrated circuit technology.

Most of reported I-III-VI2 type chalcopyrites have been developed as indispensible materials for potential application in photovoltaic solar cells, magnetism or thermoeletrics. The exploration of its photoluminescence potentials has been very limited and the chemical sensing using fluorescence to signal a recognition event is realized by way of CuFeSe2 nanocrystals. A novel solution-based synthesis strategy has been developed for the preparation of CuFeSe2 quantum dots (QDs) via oleylamine and dodecanethiol as precursors. QDs possess an intense blue luminescence at 431 nm and excitation-dependent features are recorded. The nanocrystals exhibit transformation from ferromagnetism to paramagnetism state between 4 K and 298 K. Another distinct advantage of the quantum dots will be the signaling pathway in response to external analytes. It gives rise to a rapid and selective assay of Cr2O72- through an “on-off” switching process. A linear equation can be obtained in the range from 0 to 47.5 μM and the detection limit has been determined to be 0.46 μM. This cost-effective method will pave the way for the efficient synthesis of ternary chalcopyrites and provide suitable chemical routes for sensing purposes.

GaN-based high electron mobility transistors (HEMTs) have exhibited great application prospects in power and radio frequency devices, thanks to the superior properties of GaN. Despite the significant commercialization progress, the reliability of GaN-based HEMTs remains a challenge. This work experimentally investigates the time-dependent degradation of Mg-doped GaN/AlN superlattice HEMTs under both OFF-state and SEMI-ON-state bias conditions and proposes that GaN/AlN superlattices as a barrier can solve the Vth instability issues of GaN HEMTs under OFF-state and SEMI-ON-state bias conditions. On the one hand, in the SEMI-ON-state, the hot electron effect leads to the degradation of Ig, gm,max, and Id,sat to varying degrees. However, the as-prepared GaN-based HEMTs exhibit excellent Vth stability (almost no change) under hot electron injection, on the account of the excellent two-dimensional electron gas confinement in the GaN/AlN superlattice structure. On the other hand, in the OFF-state, positive Vth shift (about 0.12 V) is induced by the hole emission in the GaN/AlN superlattice structure under reverse bias stress. In addition, the stress-induced destruction of MgO gate dielectric gives rise to the gate leakage, which increases by 2 orders of magnitude and triggers an irreversible degradation (about 10%) of the gm,max. These results are expected to provide a solution to the Vth instability of GaN HEMTs.

An efficient way to assemble Fe3O4@SiO2-NH2 nanocomposite has been developed by coupling (3-aminopropyl)trimethoxysilane onto surface of core-shell structure through facile impregnation of Fe3O4@SiO2 decorated with amino groups. The key step during the synthesis involves the incorporation of organic fluorophore and amines are treated with 1,8-naphthalic anhydride. The achieved hybrid inorganic-organic nanoparticle gives rise to blue emissions and shows enough stability. Furthermore, Cu2+ can be recognized by the organic building block via coordination reaction and the “on-off” quenching effect is observed. The nanosensor provides a response concentration range (1–6 μM) to Cu2+ with the detection limit of 0.65 μM. Owing to the magnetic properties, the hybrid nanoprobe can be easily retrieved from aqueous solution for repeated uses via magnetic separation (35 s). This approach will offer an alternative way for designing novel detection systems in biological related fields.

Since Cu2+ and Fe3+ ions have been considered as bioactive cations in oxygen transport and enzymatic reactions, the development of reliable ways for the monitoring of the two species will be highly desirable. But the optical stability of conventional organic chromophores needs to be improved. Therefore, the employment of quantum dots (quantum dots are abbreviated to be QDs) such as ternary CuFeS2 QDs for the purpose of sensing has been reported in this study. CuFeS2 QDs were synthesized by using oleylamine as the stabilizer at 180 °C and the particle size was around 2–3 nm. The monodispersed quantum dots with tetragonal chalcopyrite crystalline structure were identified. The corresponding excitation and emission wavelengths of the QDs were monitored at 372 and 458 nm. Magnetic properties were analyzed via applied magnetic field ranging between −6000 and 6000 Oe at 300 K and the ferromagnetic phase was verified. In this report, CuFeS2 QDs has been used as an optical probe to detect the metal ions with high sensitivity, selectivity and fast responses. Two linear equations can be obtained in the range from 0 to 30 μM for Cu2+ and from 0 to 45 μM for Fe3+ (detection limits: Cu2+, 1.98 μM; Fe3+, 2.15 μM). These results may provide promising applications in cation sensing fields.

Polymer dots possess superior emissive features, but most of them give rise to luminescence bands in the blue region. In addition, blue or green emissions have difficulty in penetrating tissue deeply. Therefore, long wavelength emissive signals are welcome for the development and application of polymeric dots towards sensing and bio-analysis. Herein, the color-tunable fluorescence polymer nanoparticles (F-PNPs) have been synthesized via one-step strategy based on the employment of hydroquinone and polyethyleneimine as precursors at low temperature. Moreover, its emission peak can be shifted from 523 nm to 612 nm by varying the excitation wavelength in the range of 380 nm to 480 nm. In view of sensing assessment, F-PNPs enable the quantitative determination of trace amount of SO32− and Cu2+. In the presence of SO32−, the polymer dots exhibit ratiometric fluorescence signals in deionized water and the color change from green to blue has been clearly observed by naked eyes (detection limit = 59 nM). In addition, two emission bands at 545 nm (green) and 601 nm (red) are observed to be responsive to the exposure of Cu2+. The entire dual sensing system for the detection of Cu2+ will be more accurate and reliable. The evaluation results reveal their optical signals are improved linearly due to the addition of Cu2+ at increasing concentrations and the detection limits are calculated to be 76 nM (green) and 41 nM (red), respectively. Such polymeric network will provide a new dynamic platform for sensing purposes in biomedicine study, environmental protection, and food safety.

Fluorescent organic nanoparticles (FONs) play important roles in the monitoring and controls of biological systems. To fulfill such duties, we have to investigate how the nanoplatforms interact with living matters. Currently, very limited information concerning the potential risks and toxicity has been reported for FONs except the MTT assay. In this contribution, the amine-rich cationic precursor (polyethyleneimine) initiates one-pot copolymerization with methyldopa sesquihydrate and water-soluble fluorescent nanoparticles are afforded. The influence of reduction agent (sodium sulfite) on the luminescence, microstructure and crystallinity has been discussed and the corresponding stabilities are substantially improved. Further studies reveal that selective Cu2+ detection has been realized due to “on-off” change and the limit of detection is determined to be 52 nM. It has been discovered that glutathione (GSH) can recover its green luminescence in terms of strong affinity of GSH to copper ions. For the first time, three different cell viability experiments including MTS assay, Annexin V-APC/7-AAD kit and double stain technique have been performed to support the negligible cytotoxicity of FONs in living cells. Spectra imaging has been employed for the identification of Cu2+ and GSH in HeLa cells. In addition, the Cu2+-GSH pairs can generate an “AND” logic gate during recognition sequence operations. It will be the first example that the effectiveness of encryption and decryption has been verified via Cu2+ and GSH based on FONs.