Response Of Diodes Research Articles

CdS/PbSe Heterojunction Made via Chemical Bath Deposition and Ionic Exchange Processes to Develop Low-Cost and Scalable Devices

Complete optoelectronic devices present major difficulties to be built by aqueous chemical deposition. In this work, a ITO/CdS/PbSe heterostructure was developed, depositing CdS over an ITO-coated substrate via a chemical bath deposition (CBD) technique. The next step involved the growth of a plumbonacrite film over CdS via CBD, where the film acted as a precursor film to be converted to PbSe via ion exchange. The characterization of each material involved in the heterostructure were as follows: the CdS thin films presented a hexagonal crystalline structure and bandgap of 2.42 eV; PbSe had a cubic structure and a bandgap of 0.34 eV. I vs. V measurements allowed the observation of the electrical behavior, which showed a change from an ohmic to diode response by applying a thermal annealing at 150 °C for 5 min. The forward bias of the diode response was in the order of 0.8 V, and the current-voltage characteristics were analyzed by using the modified Shockley model, obtaining an ideality factor of 2.47, being similar to a Schottky diode. Therefore, the reported process to synthesize an ITO/CdS/PbSe heterostructure by aqueous chemical methods was successful and could be used to develop optoelectronic devices.

Modeling the Response of a Microwave Low-Barrier Uncooled Mott Diode to the Action of Heavy Ions of Outer Space and Femtosecond Laser Pulses

Modeling the Response of a Microwave Low-Barrier Uncooled Mott Diode to the Action of Heavy Ions of Outer Space and Femtosecond Laser Pulses

Transient Response of the Acid-base Diode for Polarity Change

An application of the so-called acid-base diode would be the sensitive detection of nonhydrogen cations in an acidic medium based on salt-effects. For diode purposes different connecting elements between the acidic and aqueous reservoirs of the diode were developed, namely a polyvinyl alcohol (PVA) hydrogel cylinder, and a polyvinyl butyral (PVB) membrane. During the measurement of the voltage – current characteristic (VCC) of the diode, it was found, that in the case of PVA gel cylinder an overshoot (a local maximum followed by a local minimum) appeared in the time vs. current curve, while the diode was switched between modes (open or closed), that is the direction of the applied voltage was reversed. The overshoot did not appear in PVB membrane.The existence of overshoots was studied by numerical simulations. The time response of the diode with different hypothetic connecting elements was investigated, when the diode was switched between modes via changing the polarity of applied voltage. We found that larger diffusion coefficients of hydrogen and hydroxide ions explain the appearance of overshoots. By examining the concentration and potential profiles a qualitative explanation of this phenomenon was given.

Non-volatile artificial synapse based on a vortex nano-oscillator

In this work, a new mechanism to combine a non-volatile behaviour with the spin diode detection of a vortex-based spin torque nano-oscillator (STVO) is presented. Experimentally, it is observed that the spin diode response of the oscillator depends on the vortex chirality. Consequently, fixing the frequency of the incoming signal and switching the vortex chirality results in a different rectified voltage. In this way, the chirality can be deterministically controlled via the application of electrical signals injected locally in the device, resulting in a non-volatile control of the output voltage for a given input frequency. Micromagnetic simulations corroborate the experimental results and show the main contribution of the Oersted field created by the input RF current density in defining two distinct spin diode detections for different chiralities. By using two non-identical STVOs, we show how these devices can be used as programmable non-volatile synapses in artificial neural networks.

Proton Energy Loss in GaN

The proton energy loss in GaN in an energy range between 0 and 65 MeV is investigated. The energy of protons generated by a cyclotron at about 65 MeV is varied by inserting an energy‐absorbing medium of varying thickness. The precise modeling of the GaN Schottky diode response as a function of the absorbing medium thickness allows us to demonstrate that the energy absorption loss in GaN precisely follows the Bethe theory. In addition, the region of the detector contributing to its response to a proton beam, which is of prime importance for proton detector optimization, can be identified.

Simulation and Modeling of Time-Resolved X-Ray Detector for the Saturn Accelerator

We present the technology-aided computer design (TCAD) device simulation and modeling of a silicon p-i-n diode for detecting time-dependent X-ray radiation. We show that the simulated forward and reverse breakdown current–voltage characteristics agree well with the measured data under nonradiation environment by only calibrating carrier lifetimes for the forward bias case and avalanche model critical fields for the reverse bias condition. Using the calibrated parameters and other nominal material properties, we simulated the radiation responses of the p-i-n diode and compared with experimental data when the diode was exposed to X-ray radiation at Sandia’s Saturn facility and the Idaho State University (ISU) TriMeV facility. For Saturn’s Gaussian dose-rate pulses, we show three findings from TCAD simulations. First, the simulated photocurrents are in excellent agreement with the measured data for two dose-rate pulses with peak values of $1.16 \times 10 ^{10}$ and $1.88 \times 10 ^{10}$ rad(Si)/s. Second, the simulation results of high dose-rate pulses predict increased delayed photocurrents with longer time tails in the diode electrical responses due to excess carrier generation. Third, simulated peak values of diode radiation responses versus peak dose rates at different bias conditions provide useful guidance to determine the dose-rate range that the p-i-n diode can reliably detect in experiment. For TriMeV’s non-Gaussian dose-rate pulse, our simulated diode response is in decent agreement with the measured data without further calibration. We also studied the effects of device geometry, recombination process, and dose-rate enhancement via TCAD simulations to understand the higher measured response in the time after the peak dose-rate radiation for the p-i-n diode exposed to TriMeV irradiation.

Towards an optimal MIIM diode for rectennas at 10.6 μm

We investigate, for the first time, optimization of the responsivity of metal-insulator-insulator-metal (MIIM) diodes by carefully considering materials' properties. The diode's resistance is fixed at 100 Ω in order to match the nano antenna's impedance and to increase the total efficiency of the rectifying antenna (rectenna). The optimization is performed at zero-bias responsivity and resistance to ensure zero-bias operation. The diode's resistance and responsivity are calculated from the simulated current-voltage characteristics using Airy functions-based transfer matrix method (TMM) that was verified using experimental results. The design parameters of barrier heights for each insulator and metals, their dielectric constants, and the difference in the metals' work functions, are optimized to enhance the overall diode's performance. Optimal results are presented showing the beneficial effect of simultaneously varying these design parameters. Suggestions for implementing these optimal values with real materials are proposed and presented. Finally, the MIIM capacitance effect on the rectenna cut-off frequency is investigated to ensure that proposed MIIM diodes allow the rectenna to operate efficiently in the IR regime.

Bipolar Nanochannels: A Systematic Approach to Asymmetric Problems.

Nanofluidic diodes are capable of rectifying the electrical current by several orders of magnitude. In the current state of affairs, determining the rectification factor is not possible as it depends on many system parameters. In this work, we systematically scan the effects of geometry and excess counterion concentrations (i.e., surface charge effects). We show that the current-voltage response varies between the two extreme behaviors of unipolar and bipolar responses. The exact behavior depends on the geometry and surface charge properties of the system. Here, we have gone beyond the typical setup that only considers the dynamics within the nanochannel itself and we have included the effects of the adjoining microchannels. Systems that include both nanochannels and microchannels exhibit the classical signatures of concentration polarization, such as ionic depletion and enrichment. Here, where we have scanned a wide range of parameters, we show that bipolar and semi-bipolar systems exhibit a wider range of phenomena that are intrinsically more complicated. Our system characterization is for both, the much more investigated case of steady state and the less investigated, but equally interesting, time-transient case. For example, it is common to characterize the system by its steady-state result (current-voltage response, rectification factor, and transport number). Here, we demonstrate that the time-transient behavior of the fluxes can also be used to characterize the system, and that the time-dependent rectification factors and transport numbers are meaningful. The systematic approach taken in this work, and the results presented herein, can be used to further elucidate the complicated behavior of the current-voltage response of nanofluidic diodes and to rationalize experimental results. The insights of this work can be used to enhance and improve the design of all nanofluidic diodes.

Simulation of the Response of a Low-Barrier Mott Diode to the Influence of Heavy Charged Particles from Outer Space

Simulation of the Response of a Low-Barrier Mott Diode to the Influence of Heavy Charged Particles from Outer Space

Vertical-junction photodiodes for smaller pixels in retinal prostheses

Objective. To restore central vision in patients with atrophic age-related macular degeneration, we replace the lost photoreceptors with photovoltaic pixels, which convert light into current and stimulate the secondary retinal neurons. Clinical trials demonstrated prosthetic acuity closely matching the sampling limit of the 100 μm pixels, and hence smaller pixels are required for improving visual acuity. However, with smaller flat bipolar pixels, the electric field penetration depth and the photodiode responsivity significantly decrease, making the device inefficient. Smaller pixels may be enabled by (a) increasing the diode responsivity using vertical p–n junctions and (b) directing the electric field in tissue vertically. Here, we demonstrate such novel photodiodes and test the retinal stimulation in a vertical electric field. Approach. Arrays of silicon photodiodes of 55, 40, 30, and 20 μm in width, with vertical p–n junctions, were fabricated. The electric field in the retina was directed vertically using a common return electrode at the edge of the device. Optical and electronic performance of the diodes was characterized in-vitro, and retinal stimulation threshold measured by recording the visually evoked potentials in rats with retinal degeneration. Main results. The photodiodes exhibited sufficiently low dark current (<10 pA) and responsivity at 880 nm wavelength as high as 0.51 A W−1, with 85% internal quantum efficiency, independent of pixel size. Field mapping in saline demonstrated uniformity of the pixel performance in the array. The full-field stimulation threshold was as low as 0.057 mW mm−2 with 10 ms pulses, independent of pixel size. Significance. Photodiodes with vertical p–n junctions demonstrated excellent charge collection efficiency independent of pixel size, down to 20 μm. Vertically oriented electric field provides a stimulation threshold that is independent of pixel size. These results are the first steps in validation of scaling down the photovoltaic pixels for subretinal stimulation.

Influence of the design on the thermal response of press-fit diodes: An infrared thermographic study

A critical effect in the field of the power semiconductors is their heating processes under high currents regime, in the order of amperes. The thermal characterization in working conditions is not always an easy task, and its over/underestimation can lead to failures in the design of the devices. Infrared thermography measurements are shown in this work as a valuable tool to determine the temperature mapping, profiles and heating and cooling rates of diodes under working conditions. Press-fit metal-oxide semiconductors commercial diodes with different designs from two different suppliers have been analyzed. This work provides elements that relate the dissipated power and the release of heat with the design.

Spectrally resolved optical beam-induced current imaging of ESD induced defects on VCSELs

Optical beam-induced current (OBIC) mapping is widely used to characterize semiconductor lasers, particularly for failure analysis, in which the reliability has been a critical issue to be resolved spectrally and temporally. OBIC microscopy is advantageous for its non-invasiveness, when compared with electron beam-induced current (EBIC) microscopy. However, for high-speed devices, conventional OBIC methods may be limited in observing the spectral responses adequately. In this work, we present a modified OBIC microscopy based on a tunable ultrafast laser, to address the need for spectral resolving for precision failure spot analysis in vertical-cavity surface-emitting laser (VCSEL) diodes. The spectral OBIC response of VCSEL diodes is investigated by varying the irradiation wavelengths. Importantly, the ultrafast mode-locked laser provides broadband wavelength range to investigate photocurrent responses of the VCSELs sample. Specifically, the OBIC, electroluminescence (EL) detection, and the reflectance of the normal and the electrostatic discharge (ESD) damaged VCSELs are compared. We have found the ESD damaged VCSELs showing a redshifted spectral response.

Solution-Processed Donor-Acceptor Poly(3-hexylthiophene):Phenyl-C61-butyric Acid Methyl Ester Diodes for Low-Voltage α Particle Detection.

Diodes fabricated using a blend of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (6-80 μm thick) as an organic semiconductor component achieved consistent 4 MeV α particle detection. Current-voltage characteristics and current-time measurements were obtained under α irradiation and in its absence. Steady-state and transient (time-of-flight) photoconduction measurements were additionally performed. Low-bias (<20 V) α particle detection gain-efficiency products of order 10-2 were measured. The α particle detection was achieved reproducibly, reversibly, and repeatably in different devices of varying organic semiconductor layer thicknesses using both the steady-state and time-dependent (dynamic) diode responses. Conductive gain, due to trapped electrons, increased the α particle gain-efficiency product in both forward and reverse bias conditions as well as increasing steady-state photoconduction. The device thickness was optimized to maximize the gain-efficiency product by matching the penetration depth of the α particle, obtained by modeling, to the organic semiconductor layer thickness. Very high confidence α particle detection was achieved (with signal-to-noise ratios exceeding 20) under optimized device dimensions and drive conditions. Hecht function fitting of the gain-efficiency product versus electric field data returns mobility-lifetime products of order 10-6-10-7 cm2 V-1. This work demonstrates that solution-processed organic semiconductor diodes are viable for low-voltage α particle detection.

There is Plenty of Room for THz Tunneling Electron Devices Beyond the Transit Time Limit

The traditional transmission coefficient present in the original Landauer formulation, which is valid for quasi-static scenarios with working frequencies below the inverse of the electron transit time, is substituted by a novel time-dependent displacement current coefficient valid for frequencies above this limit. Our model captures in a simple way the displacement current component of the total current, which at frequencies larger than the inverse of the electron transit time can be more relevant than the particle component. The proposed model is applied to compute the response of a resonant tunneling diode from 10$\,$GHz up to 5$\,$THz. We show that tunneling electron devices are intrinsically nonlinear at such high frequencies, even under small-signal conditions, due to memory effects related to the displacement current. We show that these intrinsic nonlinearities (anharmonicities) represent an advantage, rather than a drawback, as they open the path for tunneling devices in many THz applications, and avoid further device downscaling.

Response of electron-irradiated silicon carbide Schottky power diodes at elevated temperature

Thermal-dependence experiments were executed on silicon carbide Schottky diodes. Devices were exposed to 3 MeV electrons with 10 MGy dose. Current density-voltage (~300 K to ~490 K) characterisation was used for investigation. At highest tested temperature, forward current at 0.3 V increased approximately seven orders of magnitude for unirradiated; and eight orders of magnitude for irradiated devices due to free carriers generation which obtained energy from the temperature. Series resistance of unirradiated increased with increasing temperature due to decrease in free carriers mobility, whilst irradiated devices decreased with increasing temperature which indicates that more free carriers acquired enough energy to escape the radiation-induced traps. Reverse current increased with increasing temperature due to the radiation-induced defects that act as generation-recombination centres. Activation energies of irradiated is higher than unirradiated devices. Also, there are two slopes in the plot of the activation energy-voltage which suggests that the reverse leakage current is due to two different mechanisms.

The response of low-cost photodiodes for dosimetry in electron beam processing

The response of thin diodes (SFH206k) as dosimeters has been investigated employing the beam of an electron accelerator within the dose rate range of 2–8 kGy/s and accumulated doses up to 100 kGy. These devices, operating in the short-circuit mode and under industrial irradiation conditions, deliver current signals nonlinearly dependent on the dose rate, whichever the dose history of the diodes, due to the high density of the generated electron-hole pairs herein achieved. Despite this nonlinearity, the dose rate response is stable and characterized by current signals with repeatability better than 2.0%, regardless of the accumulated dose. It is also found that the dose responses are quite linear with sensitivities slightly dependent on the accumulated dose at a constant dose rate. The decrease in the charge sensitivity, taking as reference that obtained before any radiation damage, reaches only 9% (k = 2) at 100 kGy, which is much smaller than the values reported in the literature. From this low aging and the repeatability of both dose rate and dose responses, it seems that the photodiode under investigation is a low budget alternative, good enough for routine dosimetry, provided it has been previously calibrated in the same processing facility.

Response of electron-irradiated silicon carbide Schottky power diodes at elevated temperature

Thermal-dependence experiments were executed on silicon carbide Schottky diodes. Devices were exposed to 3 MeV electrons with 10 MGy dose. Current density-voltage (~300 K to ~490 K) characterisation was used for investigation. At highest tested temperature, forward current at 0.3 V increased approximately seven orders of magnitude for unirradiated; and eight orders of magnitude for irradiated devices due to free carriers generation which obtained energy from the temperature. Series resistance of unirradiated increased with increasing temperature due to decrease in free carriers mobility, whilst irradiated devices decreased with increasing temperature which indicates that more free carriers acquired enough energy to escape the radiation-induced traps. Reverse current increased with increasing temperature due to the radiation-induced defects that act as generation-recombination centres. Activation energies of irradiated is higher than unirradiated devices. Also, there are two slopes in the plot of the activation energy-voltage which suggests that the reverse leakage current is due to two different mechanisms.

Моделирование реакции низкобарьерного диода Мотта на воздействие тяжелых заряженных частиц космического пространства

A theoretical analysis of transient ionization processes occurring in a low-barrier GaAs Mott diode under the influence of space radiation high energy charged particles and simulating pulsed laser radiation is carried out. The diode response to the As+ ion action with an energy of 200 MeV, corresponding to a linear energy transfer of 26 MeV cm2/mg, is compared with the response to the femtosecond pulses optical radiation action of various durations (10-1000 fs) and photon energies exceeding the GaAs band gap.

RESEARCH ON A MAGNETIC FIELD SENSOR WITH A FREQUENCY OUTPUT SIGNAL BASED ON A TUNNEL-RESONANCE DIODE

Based on the consideration of physical processes in a tunnel-resonant diode under the action of a magnetic field, the construction of an autogenerating magnetic field sensor with a frequency output signal is proposed. The use of devices with negative differential resistance makes it possible to significantly simplify the design of magnetic field sensors in the entire RF frequency range. Depending on the operating modes of the sensor, an output signal can be obtained in the form of harmonic oscillations, as well as in the form of pulse oscillations of a special form.&#x0D; The study of the characteristics of the magnetic field sensor is based on the complete equivalent circuit of the tunnel-resonant diode. The equivalent circuit takes into account both the capacitive and inductive properties of the tunneling resonant diode. The inductive component exists under any operating conditions, as a result of the fact that the current flowing through the device is always lagging behind the voltage that caused it, which corresponds to the inductive response of a tunnel-resonant diode.

Ammonia Gas Sensor Response of a Vertical Zinc Oxide Nanorod-Gold Junction Diode at Room Temperature

Conventional metal oxide semiconductor (MOS) gas sensors have been investigated for decades to protect our life and property. However, the traditional devices can hardly fulfill the requirements of our fast developing mobile society, because the high operating temperatures greatly limit their applications in battery-loaded portable systems that can only drive devices with low power consumption. As ammonia is gaining importance in the production and storage of hydrogen, there is an increasing demand for energy-efficient ammonia detectors. Hence, in this work, a Schottky diode resulting from the contact between zinc oxide nanorods and gold is designed to detect gaseous ammonia at room temperature with a power consumption of 625 μW. The Schottky diode gas sensors benefit from the change of barrier height in different gases as well as the catalytic effect of gold nanoparticles. This diode structure, fabricated without expensive interdigitated electrodes and displaying excellent performance at room temperature, provides a novel method to equip mobile devices with MOS gas sensors.