Overcoming the Bandwidth-Quantum Efficiency Trade-Off in Conventional Photodetectors

Optical systems and microwave photonics applications rely heavily on high-performance photodetectors having a high bandwidth-efficiency product. The main types of photodetector structures include Schottky and PIN-photodiodes, heterojunction phototransistors, avalanche photodetectors, and metal-semiconductor-metal photodetectors. Vertically-illuminated photodetectors intrinsically present bandwidth-efficiency limitations, but these have been mitigated by new innovations over the years in quantum well photodetectors, edge-coupled photodetectors and resonant-cavity enhanced photodetectors for improved photophysical characteristics. Edge-coupled ultra-high-speed photodetectors have yielded high conversion efficiencies, and the active device structure of resonant-cavity-enhanced photodetectors allows wavelength selectivity and optical field enhancement due to resonance, enabling photodetectors to be made thinner and hence faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Single-photon avalanche diodes have been developed, which combine an ultimate sensitivity with excellent timing accuracy. Further advances in addressing the bandwidth-quantum efficiency trade-off have incorporated photon-trapping nanostructures and plasmonic nanoparticles. Nanowire photodetectors have also demonstrated the highest photophysical performance to date

Towards New Generation Power MOSFETs for Automotive Electric Control Units

Power metal-oxide-semiconductor field-effect transistors (MOSFETs) are thought to be highly robust and versatile in high-speed switching applications in power electronics design due to its intrinsic high input impedance and compact size. This chapter concerns the development of a high-performance low voltage rating power MOSFET possessing low on-resistance and excellent avalanche current capability for an automotive electric power steering system (EPS). Using industry-standard Technology Computer-Aided Design (TCAD) tools, the planar- and trench-technology power MOSFETs, have been designed, modeled, simulated and compared. We surveyed and analyzed the specific on-resistance due to the different device structures, and various methods are highlighted and compared so that their benefits can be better understood and adopted. Additionally, the device ruggedness has been investigated and its improvement was evaluated and established for that of the trench MOSFET due to gate corner smoothing

Anti-reflective structures for photovoltaics: Numerical and experimental design

The effects of different anti-reflective structures on the photovoltaic performance of the silicon solar cell were studied using finite-element modelling and numerical simulations for which experiment alone does not provide a full description. The front surface reflectivity may be mitigated significantly by an anti-reflective coating (ARC) of a suitable thickness. Alternatively, nanoscale surface texturing can effectively trap a greater ratio of incident light to increase optical absorption. The optimized layer thicknesses of the ZnO single layer and SiO2/Si3N4 double layer films were calculated for minimum reflectivity, with the former grown by magnetron sputter deposition and characterized using specular X-ray reflectivity measurements. Based on geometric ray-tracing and solutions to the semiconductor equations, the theoretical photovoltaic performance was simulated and compared for a range of incident angles at an optical intensity of 0.1 Wcm−2, revealing a limit to the angular collection efficiency of the ARC at a grazing incidence angle of 30°. Using ZnO or SiO2/Si3N4 ARCs or surface texturing increases the power conversion efficiency by 20%, 24% and 30% respectively at normal incidence. The insights provided by physical-based modelling on the optimized design parameters of the anti-reflective structures confer a promising pathway for enhancing the external quantum efficiency of photovoltaic devices. Keywords: Photovoltaic cells, Surface engineering, Energy conversion, Thin films, Reflectivit

Label-Free Electrochemical Detection of Vanillin through Low-Defect Graphene Electrodes Modified with Au Nanoparticles

Graphene is an excellent modifier for the surface modification of electrochemical electrodes due to its exceptional physical properties and, for the development of graphene-based chemical and biosensors, is usually coated on glassy carbon electrodes (GCEs) via drop casting. However, the ease of aggregation and high defect content of reduced graphene oxides degrade the electrical properties. Here, we fabricated low-defect graphene electrodes by catalytically thermal treatment of HPHT diamond substrate, followed by the electrodeposition of Au nanoparticles (AuNPs) with an average size of ≈60 nm on the electrode surface using cyclic voltammetry. The Au nanoparticle-decorated graphene electrodes show a wide linear response range to vanillin from 0.2 to 40 µM with a low limit of detection of 10 nM. This work demonstrates the potential applications of graphene-based hybrid electrodes for highly sensitive chemical detection

Enhanced thermal conductivity of epoxy composites with core-shell SiC@SiO(2) nanowires

Electronic packaging materials and thermal interface materials (TIMs) are widely used in thermal management. In this study, the epoxy composites with core-shell structure SiC@SiO(2) nanowires (SiC@SiO(2) NWs) as fillers could effectively enhance the thermal conductivity of epoxy composites. The unique structure of fillers results in a high thermal conductivity of epoxy composites, which is attributed to good interfacial compatibility epoxy matrix and bridging connections of SiC@SiO(2) NWs. From neat epoxy to 2.5 wt% loading of SiC@SiO(2) NWs, the thermal conductivity is significantly increased from 0.218 to 0.391 W m^−1 K^−1, increased by 79.4%. In addition, the composite with 2.5 wt% filler possess lower coefficient of thermal expansion and better thermal stability than that of neat epoxy. All these outstanding properties imply that epoxy/SiC@SiO(2) NWs composites could be the ideal candidate for TIM