High-speed Diode Research Articles

High Performance Indium-Tin-Oxide Schottky Diodes for Terahertz Band Operation.

Schottky diode, capable of ultrahigh frequency operation, plays a critical role in modern communication systems. To develop cost-effective and widely applicable high-speed diodes, researchers have delved into thin-film semiconductors. However, a performance gap persists between thin-film diodes and conventional bulk semiconductor-based ones. Featuring high mobility and low permittivity, indium-tin-oxide has emerged to bridge this gap. Nevertheless, due to its high carrier concentration, indium-tin-oxide has predominantly been utilized as electrode rather than semiconductor. In this study, a remarkable quantum confinement induced dedoping phenomenon was discovered during the aggressive indium-tin-oxide thickness downscaling. By leveraging such a feature to change indium-tin-oxide from metal-like into semiconductor-like, in conjunction with a novel heterogeneous lateral design facilitated by an innovative digital etch, we demonstrated an indium-tin-oxide Schottky diode with a cutoff frequency reaching terahertz band. By pushing the boundaries of thin-film Schottky diodes, our research offers a potential enabler for future fifth-generation/sixth-generation networks, empowering diverse applications.

Bandwidth Analysis of High-Speed InGaN Micro-LEDs by an Equivalent Circuit Model

High-speed light-emitting diodes (LEDs) are ideal light sources for low-cost plastic optical fiber communication in data-centers and vehicles. Here, high-speed micro-LEDs based on InGaN quantum dot (QD) active region with different diameters are fabricated and characterized. The -3dB bandwidth around 3.6 GHz and 1.4 GHz are achieved in the blue and green micro-LEDs under current density less than 1 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, which can work at an environmental temperature of 125 °C. An equivalent circuit model is proposed to analyze the limiting factors of the bandwidth, using which the effects of carrier recombination and RC time constant on modulation bandwidth are separated. It is found that carrier recombination rate is fast enough and the RC constant is still the main limiting factor for the blue micro-LEDs at an injection current density of more than 500 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> even when the diameter scales down to 20 μm, while the recombination rate mainly limits the bandwidth of the green micro-LEDs.

Wirelessly powered large-area electronics for the Internet of Things

Powering the increasing number of sensor nodes used in the Internet of Things creates a technological challenge. The economic and sustainability issues of battery-powered devices mean that wirelessly powered operation—combined with environmentally friendly circuit technologies—will be needed. Large-area electronics—which can be based on organic semiconductors, amorphous metal oxide semiconductors, semiconducting carbon nanotubes and two-dimensional semiconductors—could provide a solution. Here we examine the potential of large-area electronics technology in the development of sustainable, wirelessly powered Internet of Things sensor nodes. We provide a system-level analysis of wirelessly powered sensor nodes, identifying the constraints faced by such devices and highlighting promising architectures and design approaches. We then explore the use of large-area electronics technology in wirelessly powered Internet of Things sensor nodes, with a focus on low-power transistor circuits for digital processing and signal amplification, as well as high-speed diodes and printed antennas for data communication and radiofrequency energy harvesting.

Image contrast enhancement and denoising in micro-gap weld seam detection by periodic wide-field illumination

Due to the speckle noise and welding light noise, it's still a challenge for the detection of tight weld joints by wide-field illumination. To circumvent this problem, we proposed a novel weld joint detection system by using periodic wide-field illumination. A specific frequency component can be encoded into the image sequence by modulating the intensity of the illumination. By leveraging high-speed light-emitting diode (LED) driver and high-speed camera, an image sequence can be obtained in milliseconds. Most of the light noises contain no modulation information. By extracting the modulation frequency from the image sequences, we achieved ~35% improvement in signal-to-noise ratio (SNR) of the seam image. In addition, the light noise can be removed effectively in the frequency domain. The comparisons under different welding conditions revealed that the proposed method could accurately locate the seam position in ultra-tight seam and under strong light noise while the method without modulation failed.

Numerical investigation of quantum tunneling time and spin-current density in GaAs/GaMnAs/GaAs barriers: Role of an applied bias voltage

In this paper, we have discussed theoretically the effect of an applied bias voltage and the temperature on the spin-tunneling time, spin-dependent polarization and current densities of holes in GaAs/GaMnAs double barriers using the transfer matrix method (TMM). The behavior of the transmission coefficients for different spin orientations (up and down), various applied voltages and different temperatures were calculated. Our findings indicate that the maxima of the spin-up transmission coefficient shift towards the lower energies by increasing the applied bias voltage. Furthermore, our structure is almost transparent for spin-down holes and presents some resonances for spin-up ones. In addition, we have found that the tunneling time decreases progressively by enhancing the applied voltage. It is also shown that the current densities of holes with both spin-up and down orientations present a negative differential resistance (NDR). This (NDR) resistance is more intense for spin-up holes than spin-down ones. Consequently, the obtained results pointed out that we can design and fabricate a high-speed spin-filters and diodes by fixing the appropriate values of applied voltages and temperatures.

Experimental analysis of the injection pressure effect on the near-field structure of liquid fuel sprays

Primary atomization and initial spray development are critical in the operation of high-pressure liquid sprays such as the ones used in internal combustion engines. In the current paper, an analysis of the effect of the fuel injection pressure on the near-nozzle spray morphology is performed. For this purpose, a high-magnification diffused backlight imaging technique is set by means of a high-speed light-emitting diode and a long-distance microscope. The technique allows to visualize the first 2 mm of the spray development with a resolution of approximately 250 pixels per millimeter. The images obtained are processed with two different criteria to define the spray contour: one using an optical thickness threshold and a second one based on the intensity derivative on the radial direction. The analysis is focused on three aspects of the spray morphology: the spray angle, its standard deviation, and the standard deviation of the spray contour itself. The results show that the average spray angle is only slightly affected by the injection pressure, being the discharge density the main boundary condition affecting this parameter. Instead, the two standard deviation parameters show a clear increasing trend with the injection pressure, confirming that higher turbulence at the nozzle outlet induces higher variability in the spray shape. Regarding the two contour detection methodologies, similar values are reached in the average spray angle, while some more impact is seen in the spray dispersion, although the same trends are found.

High-Speed Lens-Free Holographic Sensing of Protein Molecules Using Quantitative Agglutination Assays.

Accurate, cost-effective, easy-to-use, and point-of-care sensors for protein biomarker levels are important for disease diagnostics. A cost-effective and compact readout approach that has been used for several diagnostic applications is lens-free holographic microscopy, which provides an ultralarge field of view and submicron resolution when it is coupled with pixel super-resolution techniques. Despite its potential as a diagnostic technique, lens-free microscopy has not previously been applied to quantitative protein molecule sensing in solution, which can simplify sensing protocols and ultimately enable measurements of binding kinetics in physiological conditions. Here, we sense interferon-γ (an immune system biomarker) and NeutrAvidin molecules in solution by combining lens-free microscopy with a one-step bead-based agglutination assay, enabled by a custom high-speed light-emitting diode (LED) array and automated image processing routines. We call this a quantitative large-area binding (QLAB) sensor. The high-speed light source provides, for the first time, pixel super-resolved imaging of >104 2 μm beads in solution undergoing Brownian motion, without significant motion blur. The automated image processing routines enable the counting of individual beads and clusters, providing a quantitative sensor readout that depends on both bead and analyte concentrations. Fits to the chemical binding theory are provided. For NeutrAvidin, we find a limit of detection (LOD) of <27 ng/mL (450 pM) and a dynamic range of 2-4 orders of magnitude. For mouse interferon-γ, the LOD is <3 ng/mL (200 pM) and the dynamic range is at least 4 orders of magnitude. The QLAB sensor holds promise for point-of-care applications in low-resource communities and where protocol simplicity is important.

Antimonidation of ultrathin epitaxial aluminum nanofilms for metamorphic growth of Sb-based structures on GaAs substrates

The narrow-bandgap Sb-based semiconductors find their potential in various kinds of device applications such as high-speed, low-power transistors and mid-infrared diode lasers. However, epitaxial growth on the substrates that are commercially available in large sizes (for example, GaAs and Si) faces the fundamental challenge of lattice mismatch. Different from the conventional metamorphic growth employing a thick buffer, we adopt the approach of transforming an ultrathin epitaxial aluminum (Al) nanofilm into epitaxial AlSb to serve as the template for growth of antimonide structures. It is found that the process named “antimonidation” plays a critical role in Sb-based metamorphic growth. Our experimental results provide practical usefulness for growing semiconductor devices on lattice-mismatched substrates without using thick metamorphic buffer layers.

Wireless Power Supply for HTS Magnets: Circuit Topology Design and Cryogenic Testing

For the technical and commercial applications of HTS magnets, reliable means of power supply is always a critical issue. In this paper, a systematic topology design for charging HTS magnet without electrical contact is proposed. To get rid of current leads through ambient temperature to liquid nitrogen temperature, this approach combines an analytical circuit topology design for wireless power transfer (WPT) coupler and cryogenic rectifier to work together for powering HTS magnets. Furthermore, a prototype has been manufactured and tests have been performed in cryogenic environment to substantiate the feasibility of system. In the experiments, the air gap between two sides of coupler could vary from 30 to 100 mm, which now contains enough space to design the cooling system for HTS magnets. This system successfully charged the HTS magnet up to the highest charging current 37 A due to the WPT technology and cryogenic rectifier composed by selected high-speed diodes.

Analysis of Optical and Electrical Responses of $\boldsymbol{\mu}$ -OLED With Metallized ITO Coplanar Waveguide Electrodes Submitted to Nanosecond Electrical Pulses

In this paper, the optical and electrical pulse responses of an optimized high-speed organic light-emitting diode (OLED) is investigated as a function of the pulse duration. The original design is based on the coplanar waveguide electrodes that are implemented on a transparent and conductive oxide thin film. The designed electrodes with reduced serial resistances (13 $\Omega $ ) allow to maximize the pulse energy delivery and to feed the organic device with short electrical pulses of few nanoseconds for the first time. This is achieved by designing the electrodes to have 50- $\Omega $ characteristic impedance, thanks to microwave techniques, and by implementing small values of capacitance (4.5 pF). The experimental results demonstrate $\boldsymbol \mu $ -OLED electrical and optical responses to electrical excitation pulses as short as 2.5 ns, for the first time, and state-of-the-art current densities above 1.7 kA/cm2. Moreover, and rather unexpectedly, the developed characterization procedure to extract the reported results demonstrated the first direct measurement of the electroluminescence lifetime of organic materials in the nanosecond time scale.

An X-band pulsed electron paramagnetic resonance spectrometer with time resolution improved by a field-programmable-gate-array based pulse generator.

We report an X-band pulsed electron paramagnetic resonance (EPR) spectrometer using a Field-Programmable-Gate-Array (FPGA) based pulse generator. The microwave (MW) pulse length and pulse-pulse interval can be adjusted with 50 ps time resolution. A FPGA based pulse generator is utilized to achieve such time resolution. There are eight pulse channels integrated in the pulse generator. Each channel outputs rectangular pulses with 50 ps time resolution. The spectrometer includes a pulse forming unit, where four high-speed PIN diode switches are controlled by the pulse generator to generate MW pulses. A commercial digital storage oscilloscope is used to record the EPR signal. A customized software is developed to control the components of the spectrometer and to perform data processing task. The usefulness of high time resolution is demonstrated by the results of Rabi oscillation.

Characterization of temporal variations and feedback timescales of exhaust gas recirculation gas properties using high-speed diode laser absorption spectroscopy for next-cycle control of cyclic variability

Dilute combustion offers efficiency gains in boosted gasoline direct injection engines both through knock-limit extension and thermodynamic advantages (i.e. the effect of γ on cycle efficiency), but is limited by cyclic variability at high dilution levels. Past studies have shown that the cycle-to-cycle dynamics are a combination of deterministic and stochastic effects. The deterministic causes of cyclic variations, which arise from feedback due to exhaust gas recirculation, imply the possibility of using active control strategies for dilution limit extension. While internal exhaust gas recirculation will largely provide a next-cycle effect (short-timescale feedback), the feedback of external exhaust gas recirculation will have an effect after a delay of several cycles (long timescale). Therefore, control strategies aiming to improve engine stability at dilution limit may have to account for both short- and long-timescale feedback pathways. This study shows the results of a study examining the extent to which variations in exhaust gas recirculation composition are preserved along the exhaust gas recirculation flow path and thus the relative importance and information content of the long-timescale feedback pathway. To characterize the filtering or retention of cycle-resolved feedback information, high-speed (1–5 kHz) CO2 concentration measurements were performed simultaneously at three different locations along the low-pressure external exhaust gas recirculation loop of a four-cylinder General Motors gasoline direct injection engine using a multiplexed two-color diode laser absorption spectroscopy sensor system during steady-state and transient engine operation at various exhaust gas recirculation levels. It was determined that cycle-resolved feedback propagates through internal residual gases but is filtered out by the low-pressure exhaust gas recirculation flow system and do not reach the intake manifold. Intermediate variations driven by flow rate and compositional changes are also distinguished and identified.

Design and Dynamic Analysis of a High-Speed Organic Light-Emitting Diode

We propose a structure of a high-speed multilayer organic light-emitting diode (OLED). The different organic materials have been chosen so that the barrier potential between two adjacent layers is smaller than 0.2 eV, which causes the charge carriers to move easily between layers to reach the emitting layer. The static and dynamic behaviors of the OLED have been analyzed numerically. The results from simulation show that the proposed OLED structure has an electroluminescence delay time of about 30 ns, and hence can respond to electrical pulses with a repetition rate of 2 MHz. Moreover, the device can provide good features such as high light emission efficiency, low voltage DC driving, and thermal stability.

Intrinsic rectification in common-gated graphene field-effect transistors

Terahertz rectifying antennas (rectennas) couple micron-size antennas and high-speed diodes to convert the incident electro-magnetic radiation to useable DC power. At such frequencies, the device acting as the diode requires both a nonlinear electrical behavior and a very low parasitic capacitance. Due to their low-capacitance planar structure and high carrier mobility values, several graphene devices based on various rectification mechanisms have been previously proposed as the rectifying device in the terahertz range. In this paper, we report an asymmetric behavior in micrometer-scale rectangular CVD-grown graphene field-effect transistors (GFETs), both at 77K and room temperature (295K). The asymmetry with a measured ION/IOFF ratio as high as 1.85 is shown to originate from the slight change in graphene conductivity induced by drain-gate voltage variations. This is confirmed by simulations using a simple drift-diffusion transport model. The conclusions can be directly applied to optimize diode-connected GFETs. This nonlinear effect may also be of interest for graphene interconnect considerations as well as circuit designs using GFETs.

A Q-band low noise GaAs pHEMT MMIC power amplifier for pulse electron spin resonance spectrometer.

We present the design and development of a single stage pulse power amplifier working in the frequency range 32-38 GHz based on a monolithic microwave integrated circuit (MMIC). We have designed the MMIC power amplifier by using the commercially available packaged GaAs pseudomorphic high electron mobility transistor. The circuit fabrication and assembly process includes the elaboration of the matching networks for the MMIC power amplifier and their assembling as well as the topology outline and fabrication of the printed circuit board of the waveguide-microstrip line transitions. At room ambient temperature, the measured peak output power from the prototype amplifier is 35.5 dBm for 16.6 dBm input driving power, corresponding to 19 dB gain. The measured rise/fall time of the output microwave signal modulated by a high-speed PIN diode was obtained as 5-6 ns at 20-250 ns pulse width with 100 kHz pulse repetition rate frequency.

Full-duplex link with a unified optical OFDM signal for wired and millimeter-wave wireless accesses based on direct detection

This paper proposes a full-duplex link with a downlink unified optical orthogonal frequency division multiplexing (OFDM) signal, to support wired and 60GHz band wireless accesses alternatively based on direct detection. At the optical line terminal (OLT), the downlink unified optical signal is produced via LiNbO3 Mach-Zehnder modulators (MZMs) and an interleaver. At hybrid optical network unit (HONU), it is detected by a high-speed photoelectric diode (PD) to generate a 10GHz IF-OFDM and a 60GHz RF-OFDM signals as well as an additional RF clock at 50GHz. Since the uplink optical carrier is abstracted from downlink, the HONU is free from the light source; and because part of the 50GHz RF clock is abstracted and used as the wireless uplink local RF carrier, the wireless terminal is free from the RF source. This reduces the system complexity and cost. Moreover, only one tone of the downlink unified optical signal carries the OFDM signal, which makes it suffers little from the fiber chromatic dispersion and laser phase noise. A proof-of-concept full-duplex access link over 25km fiber is conducted by simulation to demonstrate the feasibility of our proposed scheme and the link performance are assessed.

A two-angle far-field microscope imaging technique for spray flows

Backlight imaging is frequently used for the visualization of multiphase flows, where with appropriate microscope lenses, quantitative information on the spray structure can be attained. However, a key issue resides in the nature of the measurement which relies on a single viewing angle, hence preventing imaging of all liquid structures and features, such as those located behind other fragments. This paper presents results from an extensive experimental study aimed as a step forward towards resolving this problem by using a pair of high speed cameras oriented at 90 degrees to each other, and synchronized to two high-speed diode lasers. Both cameras are used with long distance microscope lenses. The images are processed as pairs allowing for identification and classification of the same liquid structure from two perspectives at high temporal (5 kHz) and spatial resolution (∼3 μm). Using a controlled mono-disperse spray, simultaneous, time-resolved visualization of the same spherical object being focused on one plane while de-focused on the other plane 90 degrees to the first has allowed for a quantification of shot-to-shot defocused size measurement error. An extensive error analysis is performed for spheroidal structures imaged from two angles and the dual angle technique is extended to measure the volume of non-spherical fragments for the first time, by ‘discretising’ a fragment into a number of constituent ellipses. Error analysis is performed based on measuring the known volumes of solid arbitrary shapes, and volume estimates were found to be within ∼11% of the real volume for representative ‘ligament-like’ shapes. The contribution concludes by applying the ellipsoidal method to a real spray consisting of multiple non-spherical fragments. This extended approach clearly demonstrates potential to yield novel volume weighted quantities of non-spherical objects in turbulent multiphase flow applications.

Room Temperature Processed Ultrahigh-Frequency Indium-Gallium–Zinc-Oxide Schottky Diode

Despite being one of the most promising amorphous semiconductors, indium-gallium-zinc oxide (IGZO) has been mostly studied in transistors at low frequencies with limited effort on high-speed diodes. In this letter, the IGZO Schottky diodes with different active areas are fabricated in co-planar microwave waveguides on glass substrates at room temperature. By reducing the area of the diode, the cutoff frequency at zero bias can be improved. We are able to show that the diode with the active area of 200 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has an intrinsic cutoff frequency beyond 20 GHz. By connecting the diode with a load, the rectifying circuit also exhibits a cutoff frequency of 4.2 GHz with the input power of 15 dBm. Simulations based on the diode properties are performed to include intrinsic and extrinsic components, and the results agree well with the experimental data.

GaAs- A3B5 heterostructures for high-speed power diodes manufacturing

Physical basis of using the controlled defect formation in InGaAs heteroepitaxial layers to vary the carrier lifetime is considered. It is shown that the lifetime of nonequilibrium carriers in the base layers of a diode can be controllably varied from several to hundreds of nanoseconds. The results obtained in a study of (i) structural defects and their rearrangement related to the lattice mismatch between the heteroepitaxial InGaAs layer and the GaAs substrate and (ii) influence exerted by these defects on the carrier lifetime and on the voltage blocked by diode structures are reported. Dynamic switching characteristics of high-speed power heteroepitaxial diodes at different temperatures are presented.

Rectennas at optical frequencies: How to analyze the response

Optical rectennas, antenna-coupled diode rectifiers that receive optical-frequency electromagnetic radiation and convert it to DC output, have been proposed for use in harvesting electromagnetic radiation from a blackbody source. The operation of these devices is qualitatively different from that of lower-frequency rectennas, and their design requires a new approach. To that end, we present a method to determine the rectenna response to high frequency illumination. It combines classical circuit analysis with classical and quantum-based photon-assisted tunneling response of a high-speed diode. We demonstrate the method by calculating the rectenna response for low and high frequency monochromatic illumination, and for radiation from a blackbody source. Such a blackbody source can be a hot body generating waste heat, or radiation from the sun.