High drain-current-density and high breakdown-field Al0.36Ga0.64N-channel heterojunction filed-effect transistors with a dual AlN/AlGaInN barrier layer

In this study, we fabricated and characterized heterojunction field-effect transistors (HFETs) based on an Al0.36Ga0.64N-channel heterostructure with a dual AlN/AlGaInN barrier layer. The device fabrication was accomplished by adopting a regrown n++-GaN layer for ohmic contacts. The fabricated HFETs with a gate length of 2 μm and a gate-to-drain distance of 6 μm exhibited an on-state drain current density as high as approximately 270 mA/mm and an off-state breakdown voltage of approximately 1 kV, which corresponds to an off-state critical electric field of 166 V/μm. This breakdown field, as a comparison in devices without field-plate electrodes, reaches approximately four-fold higher than that for conventional GaN-channel HFETs and was considered quite reasonable as an Al0.36Ga0.64N-channel transistor. It was also confirmed that the devices adopting the dual AlN/AlGaInN barrier layer showed approximately one order of magnitude smaller gate leakage currents than those for devices without the top AlN barrier layer.

Graphene as a Piezoresistive Material in Strain Sensing Applications

High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted.

Optical Properties of Cu2O Thin Films Impregnated with Carbon Nanotube (CNT)

This study investigates CNT-doped Cu2O thin film deposited by spray pyrolysis technique at a substrate temperature of 100°C. The samples were annealed at temperatures of 200°C and 230°C for 30 minutes. The effect of CNT doping on certain optical properties, such as extinction and absorption coefficients, a refractive index of doped Cu2O thin films were examined. The absorbance of the doped samples increases within the visible range and decreases in the ultraviolet range of the electromagnetic spectrum (EM). Both absorbance and extinction coefficients increased with temperature making the samples a good candidate for use as absorbance layer in device fabrication. In addition, there was an increase in direct bandgap with the increase in CNT concentration of the thin films. The result of the study revealed that CNT doping has a significant effect on the properties of Cu2O.

Diamond/GaN HEMTs: Where from and Where To?

Gallium nitride is a wide bandgap semiconductor material with high electric field strength and electron mobility that translate in a tremendous potential for radio-frequency communications and renewable energy generation, amongst other areas. However, due to the particular architecture of GaN high electron mobility transistors, the relatively low thermal conductivity of the material induces the appearance of localized hotspots that degrade the devices performance and compromise their long term reliability. On the search of effective thermal management solutions, the integration of GaN and synthetic diamond with high thermal conductivity and electric breakdown strength shows a tremendous potential. A significant effort has been made in the past few years by both academic and industrial players in the search of a technological process that allows the integration of both materials and the fabrication of high performance and high reliability hybrid devices. Different approaches have been proposed, such as the development of diamond/GaN wafers for further device fabrication or the capping of passivated GaN devices with diamond films. This paper describes in detail the potential and technical challenges of each approach and presents and discusses their advantages and disadvantages.

3D Printed Polymer Photonic Topological Insulators and their Robustness to Fabrication Disorder

Photonic topological insulators have emerged as an exciting new platform for backscatter-free waveguiding even in the presence of defects, with applications in robust long-range energy and quantum information transfer, spectroscopy and sensing, chiral quantum optics, and optoelectronics. We demonstrate a design for spin-Hall photonic topological insulators with remarkably low refractive index contrast, enabling the synthesis of photonic topological waveguides from polymeric materials for the first time. Our design is compatible with additive manufacturing methods, including fused filament fabrication for microwave frequencies, and constitutes the first demonstration of a 3D printed all-dielectric photonic topological insulator. We combine rapid device fabrication through 3D printing with high-speed FDTD simulation to quantify topological protection of transmission through “omega” shaped bent topological waveguides and find that one corner in the waveguide is 3-5 times more robust to disorder than the other. This dichotomy, a new empirical design rule for ℤ2 topological insulator devices, is shown to originate in the fundamental system symmetries and is illustrated via the distributions of Poynting vectors that describe energy flow through the waveguide. Taken together, our demonstration of 3D printed polymeric spin-Hall photonic topological insulators paired with quantification of robustness to disorder at bent topological interfaces provides a rapid, flexible scheme for engineering high-performance topological photonic devices across multiple frequency regimes from microwave to THz, to visible.

Integration technologies for chips with 2D materials

With compact footprint, low energy consumption, high scalability, and mass producibility, chip-scale integrated devices are an indispensable part of modern technological change and development. Recent advances in two-dimensional (2D) layered materials with their unique structures and distinctive properties have motivated their on-chip integration, yielding a variety of functional devices with superior performance and new features. To realize integrated devices incorporating 2D materials, it requires a diverse range of device fabrication techniques, which are of fundamental importance to achieve good performance and high reproducibility. This paper reviews the state-of-art fabrication techniques for the on-chip integration of 2D materials. First, an overview of the material properties and on-chip applications of 2D materials is provided. Second, different approaches used for integrating 2D materials on chips are comprehensively reviewed, which are categorized into material synthesis, on-chip transfer, film patterning, and property tuning / modification. Third, the methods for integrating 2D van der Waals heterostructures are also discussed and summarized. Finally, the current challenges and future perspectives are highlighted.

The Impact of the Surface Modification on Tin-Doped Indium Oxide Nanocomposite Properties

This review provides an analysis of the theoretical methods to study the effects of surface modification on structural properties of nanostructured indium tin oxide (ITO), mainly by organic compounds. The computational data are compared with experimental data such as X-ray diffraction (XRD), atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDS) data with the focus on optoelectronic and electrocatalytic properties of the surface to investigate potential relations of these properties and applications of ITO in fields such as biosensing and electronic device fabrication. Our analysis shows that the change in optoelectronic properties of the surface is mainly due to functionalizing the surface with organic molecules and that the electrocatalytic properties vary as a function of size.

Inherent characteristics of ultra-photosensitive Al/Cu–CeO2/p-Si metal oxide semiconductor diodes

An ultrahigh photosensitive diode was developed using a Cu-doped CeO2 thin film through spray pyrolysis processing, which has made a unique contribution in the field of optoelectronic device fabrication process.

A Nd6 Molecular Butterfly: An Unique All-in-One Material for SMM, MCE and Maiden Photosensitized Opto-electronic Device Fabrication

Besides iron, ironically neodymium is the most ubiquitously used metal for magnetic purposes yet it ranked among least studied metals, even among the lanthanides, when it comes to the field...