Ultrathin Mixed Ionic-Electronic Conducting Interlayer via the Solution Shearing Technique for High-Performance Lithium-Sulfur Batteries.

The commercialization of lithium-sulfur (Li-S) batteries has been hampered by diverse challenges, including the shuttle phenomenon and low electrical/ionic conductivity of lithium sulfide and sulfur. To address these issues, extensive research has been devoted to developing multifunctional interlayers. However, interlayers capable of simultaneously suppressing the polysulfide (PS) shuttle and ensuring stable electrical and ionic conductivity are relatively uncommon. Moreover, the use of thick and heavy interlayers results in an unavoidable decline in the energy density of Li-S batteries. We developed an ultrathin (750 nm), lightweight (0.182 mg cm-2) interlayer that facilitates mixed ionic-electronic conduction using the solution shearing technique. The interlayer, composed of carbon nanotube (CNT)/Nafion/poly-3,4-ethylenedioxythiophene:tetracyanoborate (PEDOT:TCB), effectively suppresses the shuttle phenomenon through the synergistic segregation and adsorption effects on PSs by Nafion and CNT/PEDOT, respectively. Furthermore, the electrical/ionic conductivity of the interlayer can be improved via counterion exchange and homogeneous Li+ ion flux/good wettability from SO3- functional group of Nafion, respectively. Enhanced sulfur utilization and reaction kinetics through polysulfide shuttle inhibition and facilitated electron/ion transfer by interlayer enable a high discharge capacity of 1029 mA h g-1 in the Li-S pouch cell under a high sulfur loading of 5.3 mg cm-2 and low electrolyte/sulfur ratio of 5 µL mg-1.

High Sensitive pH Sensor Based on AlInN/GaN Heterostructure Transistor.

The AlInN/GaN high-electron-mobility-transistor (HEMT) indicates better performances compared with the traditional AlGaN/GaN HEMTs. The present work investigated the pH sensor functionality of an analogous HEMT AlInN/GaN device with an open gate. It was shown that the Al0.83In0.17N/GaN device demonstrates excellent pH sense functionality in aqueous solutions, exhibiting higher sensitivity (−30.83 μA/pH for AlInN/GaN and −4.6 μA/pH for AlGaN/GaN) and a faster response time, lower degradation and good stability with respect to the AlGaN/GaN device, which is attributed to higher two-dimensional electron gas (2DEG) density and a thinner barrier layer in Al0.83In0.17N/GaN owning to lattice matching. On the other hand, the open gate geometry was found to affect the pH sensitivity obviously. Properly increasing the width and shortening the length of the open gate area could enhance the sensitivity. However, when the open gate width is too larger or too small, the pH sensitivity would be suppressed conversely. Designing an optimal ratio of the width to the length is important for achieving high sensitivity. This work suggests that the AlInN/GaN-based 2DEG carrier modulated devices would be good candidates for high-performance pH sensors and other related applications.

Performance of AlGaN/GaN Nanowire Omega-Shaped-Gate Fin-Shaped Field-Effect Transistor.

The AlGaN/GaN nanowire omega-shaped-gate FinFET have been successfully fabricated demonstrating much improved performance compared to conventional AlGaN/GaN MISHFET. The AlGaN/GaN omega-shaped-gate FinFET exhibited the remarkable on-state performances, such as maximum drain current of 1.1 A/mm, low on-resistance, and low current collapse compared to that of the conventional device structure. In addition, the excellent off-state performances were measured: low off-state leakage current as low as -10(-10) mA, the theoretical SS value of -62 mV/dec, and high I(ON)/I(OFF) ratio (-10(9)). Improved dc performances were obtained for omega-shaped-gate structure due to the fully depletion of the active fin body and perfectly separation of the depleted fin from the underlying thick GaN buffer layer. Furthermore, the additional reason for the enhanced device performance of the proposed device is the improved gate controllability compared to the conventional MISHFET. The proposed nano-structure device is very promising candidate for the steep switching device applications.

Design and analysis of vertical-channel gallium nitride (GaN) junctionless nanowire transistors (JNT).

Vertical-channel gallium nitride (GaN) junctionless nanowire transistor (JNT) has been designed and characterized by technology computer-aided design (TCAD) simulations. Various characteristics such as wide bandgap, strong polariztion field, and high electron velocity make GaN one of the attractive materials in advanced electronics in recent times. Nanowire-structured GaN can be applicable to various transistors for enhanced electrical performances by its geometrical feature. In this paper, we analyze the direct-current (DC) characteristics depending on various channel doping concentrations (N(ch)) and nanowire radii (R(NW)). Furthermore, the radio-frequency (RF) characteristics under optimized conditions are extracted by small-signal equivalent circuit modeling. For the optimally designed vertical GaN JNT demonstrated on-state current (I(on)) of 345 µA/µm and off-state current (I(off)) of 3.7 x 10(-18) A/µm with a threshold voltage (V(t)) of 0.22 V, and subthreshold swing (S) of 68 mV/dec. Besides, f(T) and f(max) under different operating conditions (gate voltage, V(GS)) have been obtained.