Reverse Bias Voltage Research Articles

Optoelectronic properties of laser-beam-patterned few-layer lateral MoS2 Schottky junctions

Atomically thin (or few-layer) two-dimensional transition metal dichalcogenide (TMDC) materials have various unique optoelectronic properties, which bring advantages for application to flexible solar cells and photodetectors, by bandgap engineering via van der Waals hybridization. TMDCs have crystal phase structures, such as the 2H semiconducting phase and the 1T (or 1T′) metallic phase. Recently, we demonstrated the creation of few-atom-layer 1T-metal/2H-semiconductor molybdenum disulphide (MoS2) lateral Schottky junctions by using electron beam (EB) irradiation and revealed their unique optoelectronic properties. However, the 1T phase is metastable, whereas the 1T′ phase is more stable and useful for various applications. Here, we create a few-layer 1T′-metal phase MoS2 by laser beam irradiation, which is a simpler, convenient, and low-cost method compared to EB irradiation. We observe unique optoelectronic features of the few-atom-layer 1T′-metal/2H-semiconductor lateral Schottky junctions in reverse bias voltage regions, such as an effective barrier height of ∼0.15 eV, highly efficient photogeneration ratios (>20%), and high sensitivity to photoirradiation angles without degradation for one month. These properties show great promise for application to highly efficient, flexible, and semitransparent photodetectors and solar cells with long-term reliability.

IBIC analysis of SiC detectors developed for fusion applications

In this work, we consider a 4H-SiC detector as a plasma diagnostic system for the detection of fusion-born alpha particles in future nuclear fusion reactors. A nuclear microprobe was used to locally irradiate micrometer-sized regions of the detector with 3.5 MeV He ions to fluences from 5 × 109 to 5 × 1011 cm-2. Ion Beam Induced Charge (IBIC) microscopy was employed to study its degradation in Charge Collection Efficiency (CCE) and energy resolution after irradiation. At high reverse-bias voltages, both parameters remain practically unaffected for fluences up to 1 × 1011 cm-2, while a significant deterioration of the spectroscopic performance was observed above 3 × 1011 cm-2. A theoretical drift-diffusion model, in combination with Shockley-Read-Hall recombination statistics, was used to obtain the holes lifetime from the fitting of the experimental CCE values measured at different reverse voltages. Holes lifetime was found to strongly decrease with increasing particle fluence, changing from 57 ns in pristine detectors to 0.2 ns after irradiation with a fluence of 1 × 1011 cm-2.

Design and Implementation of a Compact Single-Photon Counting Module

A compact single-photon counting module that can accurately control the bias voltage and hold-off time is developed in this work. The module is a microcontroller-based system which mainly consists of a microcontroller, a programmable negative voltage generator, a silicon-based single-photon avalanche diode, and an integrated active quench and reset circuit. The module is 3.8 cm × 3.6 cm × 2 cm in size and can communicate with the end user and be powered through a USB cable (5 V). In this module, the bias voltage of the single-photon avalanche diode (SPAD) is precisely controllable from −14 V ~ −38 V and the hold-off time (consequently the dead time) of the SPAD can be adjusted from a few nanoseconds to around 1.6 μs with a setting resolution of ∼6.5 ns. Experimental results show that the module achieves a minimum dead time of around 28.5 ns, giving a saturation counting rate of around 35 Mcounts/s. Results also show that at a controlled reverse bias voltage of 26.8 V, the dark count rate measured is about 300 counts/s and the timing jitter measured is about 158 ps. Photodetection probability measurements show that the module is suited for detection of visible light from 450 nm to 800 nm with a 40% peak photon detection efficiency achieved at around 600 nm.

Impact of Resistance on the Performance of Ultraviolet 4H-SiC Avalanche Photodiodes

In this work, ultraviolet (UV) 4H-SiC avalanche photodiodes (APDs) with a diameter of $\mu \text{m}$ were fabricated and investigated. The impact of resistance on the performance of 4H-SiC APDs was analyzed both in linear and Geiger modes. The optical response time of the fabricated APD devices in linear mode was measured with various load resistances, whereas the single photon counting performance in Geiger mode was carried out based on the passive-quenching circuit with different quenching resistances. The results show that the response time and the single-photon counting performance are strongly dependent on the series resistances. The response time (i.e., rising time and falling time) in the linear mode increases almost linearly with the load resistance increasing. In the Geiger mode, the photon count rate (PCR) decreases with the increasing quenching resistance. However, at some reverse bias voltages, the ratio of single photon detection efficiency (SPDE) to dark count rate (DCR) is positively correlated to the quenching resistance. Therefore, in order to obtain the optimal performance of 4H-SiC APDs, the resistance in the circuit must be carefully adjusted for practical usage. The results in this work will be very useful and can provide a reference for researchers in the fields of 4H-SiC APD UV detectors.

Carrier transport mechanisms of reactively direct current magnetron sputtered tungsten oxide/n-type crystalline silicon heterojunction

For optimizing the performance of tungsten oxide (WOx)/c-Si heterojunction solar cells, it is important to understand the carrier transport process within the device. Recently, several studies examined transport mechanisms; but yet reported not apparently. In this study, the fundamental carrier transport mechanisms in WOx/c-Si heterojunction solar cells and their effects on the device characteristics are investigated. Our results indicate that the trap-assisted-tunneling (TAT) process is the dominant carrier transport mechanism in the forward-bias voltage regime, while the generation of current in the space-charge region is dominant in the reverse-bias voltage regime. Interestingly, it was found that the hole-selective contact with lower oxygen-to-tungsten ratios, which is related to that of high trap densities, can assist the TAT process and increase the fill factor of the device regardless of the film conductivity. This finding is inconsistent with those of previous experiments but is consistent with those of previous simulations. Finally, this confirmation can help with optimization of WOx/c-Si heterojunction solar-cell efficiencies.

RTS Noise Detection and Voltage Effect on RTS in HgCdTe Focal-Plane Arrays

An automated random telegraph signal (RTS) detection and characterization method and a blinking noise and slow drift separation method adapted to focal-plane arrays have been developed and applied to study the evolution of the number of RTS pixels and the amplitude of the blinking signal as functions of the reverse bias voltage and temperature. The results show that the physical characteristics of the RTS follow Arrhenius laws and increase with bias. The origin of this increase in the amplitude as a function of the reverse bias is discussed.

Phenol red based hybrid photodiode for optical detector applications

In this study, the phenol red (PR) dye film has been deposited on n-type silicon wafer and SEM, XRD measurements of the film have taken. Then, the PR/n-Si photodiode has been fabricated and (dark) electrical and photoresponse characterization has been analysed. The current-Voltage (I-V) measurements have been carried out at varied light power ranging from 100 mW/cm2 to 400 mW/cm2. Rectification ratios (RR) have been determined as a function of illumination intensities and they are determined as 115.47 for 100 mW/cm2 and 30.26 for 400 100 mW/cm2, respectively. The ideality factor and the barrier height of the Co/PR/n-Si photodiode have been determined as 2.80 and 0.52 eV, respectively in dark. Therefore, it has been seen that the PR/n-Si photodiode performances are strongly dependent on the incident optical power. Namely, the current density has increased remarkably with the power of light at the same reverse bias voltage and this behavior is explained by strong capability of converting a light signal into an electrical for the PR/n-Si photodiode device. Responsivity (R) and detectivity (D*) of the PR/n-Si photodiode are also plotted as a function of illumination intensities for reverse biases and it is found that both parameters are dependent on the illumination intensity. Finally, the capacitance–voltage (C-V) characteristics of the device have been carried out at various frequencies. Obtained experimental results indicate that the PR dye can be used in various optoelectronic applications.

Second-harmonic generation in periodically poled silicon waveguides with lateral p-i-n junctions.

Electric-field-induced second-harmonic generation is demonstrated in silicon waveguides with reverse biased lateral p-i-n junctions. Phase matching is achieved by periodically poling the applied electric field. Two different poling configurations are compared: in the first, the p- and n-type doped regions of the junctions are on different sides of the waveguide (simple configuration), while in the second, they are alternated periodically across the waveguide sides (interdigitated configuration). Both simulations and experiments show that the generation efficiency is increased by 10 times comparing the interdigitated and simple configurations. The effective second-order susceptibility modulation obtained at a reverse bias voltage of 3.5 V is Δχeff,S(2)≃0.14pm/V for the simple configuration and Δχeff,I(2)≃0.64pm/V for the interdigitated one.

Effect of Franz–Keldysh absorption on the short optical pulse generation in Transistor Laser

In this work, the effect of Franz–Keldysh (FK) absorption on the short optical pulse generation in Transistor Laser (TL) is analyzed. Franz–Keldysh (F–K) Absorption coefficient is incorporated in the rate equations and solved numerically by fourth order Runge–Kutta (R–K) method. Short optical pulses are generated for various values of collector to base voltage. The output optical power is found to decrease with increasing reverse collector to base voltage. The magnitude of peak optical power and full width half maximum (FWHM) are predicted for various values of VCB. The collector base reverse bias voltage is varied from 0 V to 3 V. The peak optical pulse power is found to decrease with increasing reverse collector to base voltage. Full width half maximum is found to increase with increasing reverse collector to base voltage (VCB). The maximum peak optical power of 156.2 mW and minimum FWHM of 17.97 ps are predicted for the unbiased VCB at the base current amplitude of 128 mA. The optimum value of peak optical pulse power of 45.89 mW and full wave half maximum of 24.21 ps are obtained for the VCB value of 1.5 V at the base current amplitude of 96 mA.

Interesting Odd–Even Effect, Ohmic Contact, Negative Differential Resistance, and Current Stabilizer Behavior in All-Carbon Graphyne/Carbon-Chain Junctions

A new and simple kind of all-carbon junction nanodevice, which is free of metal electrodes, is constructed by carbon chains seamlessly connected to two graphyne nanoribbons (GYNRs) electrodes. The electron transport properties of the constructed nanodevices are systematically investigated using self-consistent charge density-functional tight-binding combined with nonequilibrium Green’s function (NEGF) formalism. The effects of contact type and contact position on the electron transport properties of these devices are discussed. The calculated results show that the electron transport properties can be well modulated by the contact geometry of the carbon chain. In GYNRs connected by both horizontal and tilted single-carbon chain, an evident even–odd behavior of conductivity is observed. In addition, the linear, monotonous currents in a wide bias voltage range show good Ohmic contact. The negative differential resistance also appears under both positive and reverse bias voltages, indicating applications in bidirectional tunnel diodes. Comprehensive analyses of the physical mechanisms for the odd–even behavior are given. Remarkably, in GYNRs connected by double-carbon chains, a noticeable current stabilizer behavior occurs, suggesting that the graphyne nanodevices contacted with double-carbon chains can be used as a current stabilizer in circuits. This article provides valuable insight into all-carbon functional nanodevices.

The Blue Light Defects Activation in A-Si:H Pin Photodiode as a Biosensor

The microfluidic Lab-On-Chip (LOC) systems, based on the CMOS technology, today grow rapidly based on requirement of the Point-of-care-testing (POCT). It is a need for a high sensitive biotransducers, as a part of biosensors to be integrated on LOC system. To detect low-level of light emitted by an analyte, promising material and devices are a p-i-n a-Si:H photodiodes. The observed absorbance of blue light in human cells HeLa (cervical carcinoma) induct H2O2 in same cells and consequently, chemical reaction with NO, detected as chemiluminescence signal by the photodiode, as well as formation of cytotoxic singlet oxygen. On the other side a-Si:H p-i-n photodiode has a high sensitivity on blue light at low-light intensity, good spectral responsivity and small reflectance for blue light, low dark current, low-noise in the range of low reverse bias voltages. The photoconductivity of a-Si:H p-i-n photodiode is influenced by the native and light induced localized state density and their energy distribution in the energy gap of intrinsic a-Si:H. It is observed that the defect states of i-layer at various bias voltages contribute to the detection of HeLa cells chemiluminescence. The optical bias dependence of modulated photocurrent method (OBMPC) using the blue LED light is applied to clarify the energy gap density of state nature and energy distribution, respectively in a-Si:H p-i-n photodiode i-layer.

High-performance mid-wavelength InAs avalanche photodiode using AlAs0.13Sb0.87 as the multiplication layer

We report on a high-performance mid-wavelength infrared avalanche photodetector (APD) with separate absorption and multiplication regions. InAs is used as the absorber material and high-bandgap AlAs 0.13 Sb 0.87 is used as the multiplication material. At room temperature, the APD’s peak response wavelength is 3.27 μm, and the 50% cutoff wavelength is 3.5 μm. The avalanche gain reaches 13.1 and the responsivity is 8.09 A/W at 3.27 μm when the applied reverse bias voltage is 14.6 V. The measured peak detectivity D ⋆ of the device is 2.05 × 10 9 cm · Hz 0.5 / W at 3.27 μm.

CSRR‐loaded UWB monopole antenna with electronically tunable triple band‐notch characteristics for cognitive radio applications

AbstractThis article introduces a compact configuration of printed monopole antenna with electronically tunable band‐notched function for ultra‐wideband (UWB) applications. A partially grounded rectangular shaped monopole is designed initially to achieve UWB behavior. The notch characteristics are then introduced by employing three complementary split‐ring resonators (CSRRs) on the radiating surface. The proposed antenna exhibits an ultra‐wide operating band ranging from 1.98 to 10.54 GHz with the notched frequencies at 2.37, 3.03, and 4.18 GHz, respectively. In order to accomplish versatility in the antenna operation, the notched frequencies are controlled electronically by implementing three varactor diodes in between the split‐ring slots. By applying an appropriate reverse bias voltage, the triple notched bands are tuned over the frequency bands: 1.58‐2.12 GHz, 2.24‐2.68 GHz, and 3.08‐3.78 GHz, respectively. A prototype with an overall dimension of 34.9 × 31.3 × 1.6 mm3 has been fabricated to experimentally determine the tuning capability of the antenna structure. The experimental result establishes close correspondence with the simulated antenna properties. The suggested antenna can be implemented practically to reject interferences from complete 1.5‐2.1 GHz LTE systems, and 2.5/3.5 GHz‐WiMAX bands, simultaneously. The capability of tuning three notched‐bands together is distinctive and has not been reported in the published literature to the best of authors' knowledge.

Coherent anti-Stokes Raman scattering imaging using silicon photomultipliers.

Silicon photomultipliers (SiPMs) are an emerging solid-state alternative to photomultiplier tubes (PMTs) for low light detection, with similar gain but lower cost and lower operating voltage. We demonstrate coherent anti-Stokes Raman scattering (CARS) imaging in a side-by-side comparison of an uncooled SiPM with an uncooled multialkali PMT as well as a state-of-the-art cooled GaAsP PMT. We determine the optimum reverse-bias voltage for acquiring the best signal-to-noise ratio (SNR) for CARS imaging of lipids at ${2850}\;{{\rm cm}^{ - 1}}$2850cm-1. We find that despite the higher dark counts, the SNR of CARS images acquired with the uncooled SiPM biased at an optimum voltage is better than that of the multialkali PMT and close to that of the cooled GaAsP PMT (${\sim}{1.5}$∼1.5 and ${\sim}{0.8}$∼0.8 times, respectively). This is due to the higher gain and lower excess noise factor related to the pulse height variability in the SiPM.

Electron and ion transmission of the gating foil for the TPC in the ILC experiment

We have developed a gating foil for the time projection chamber envisaged as a central tracker for the international linear collider experiment. It has a structure similar to the Gas Electron Multiplier (GEM) with a higher optical aperture ratio and functions as an ion gate without gas amplification. The transmission rate for electrons was measured in a counting mode for a wide range of the voltages applied across the foil using an 55Fe source and a laser in the absence of a magnetic field. The upper limit of the transmission rate for positive ions was estimated to be 3.36 ± 0.05 (stat. only)) × 10−4 from the measured electron transmission at a relatively low reverse bias voltage applied to the foil (ΔV =−15.5 V). The blocking power of the gating foil was confirmed to be high enough to suppress the influence of ion backflow.

Exploring conduction mechanism and photoresponse in P-GaN/n-MoS2 heterojunction diode

Mixed-dimensional heterostructures have shown their potential in electronic devices. However, their functionality is limited by a complete understanding of the contacts and the current transport behavior. Here, we explore the electrical properties of the P-n heterojunction diode fabricated using p-type gallium nitride and layered molybdenum disulfide. The resulting P-n diode is rectifying in nature with current rectification of three orders of magnitude. The careful choice of Ohmic contacts on both the semiconductors reveals distinctly rectifying behavior of the heterojunction diode. The as-fabricated diode is tested at various temperatures, and the conduction mechanism in the device is analyzed based on the temperature dependent electrical characterizations. In addition, photoresponse characterization reveals that the P-n heterojunction is highly sensitive to a 405 nm laser with a high responsivity of 444 A/W at a reverse bias voltage of 5 V and shows photovoltaic behavior. The heterojunction diode acts as a self-powered photodetector. Our findings show the potential of the MoS2/GaN heterojunction in highly efficient photodetector applications.

Electroluminescence from amorphous GIZO/p-GaN heterojunction light-emitting diodes

The electroluminescence from the amorphous gallium-indium-zinc oxide (a-GIZO)/p-GaN heterojunction light-emitting diodes (LEDs) were demonstrated. The heterojunction LEDs showed a current flow under both forward and reverse bias voltages. The light emissions were observed at around 410 nm (originating from p-GaN) and ~450–800 nm (originating from interfacial layer and/or from a-GIZO), which were particularly pronounced under reverse bias condition. As a result, the standard white light with the chromaticity coordinate of (0.2899, 0.3034) was obtained.

Avalanche Photodiode Array Based on InGaAs/InAlAs/InP Heteroepitaxial Structures with Separated Absorption and Multiplication Regions

In this paper, we analyze the design features of avalanche photodiode architectures with separated absorption (InGaAs) and multiplication (InAlAs) regions. Two architectures are considered: p+–M–с–i–n+- and p+–i–с–M–n+-types implemented in InGaAs/InAlAs/InP heteroepitaxial structures (HES). Three main layers, absorbing (i), charge (c), and multiplying (M), were mandatory for each architecture. Matrices of photosensitive elements were formed using data from InGaAs/InAlAs/InP HES grown via MOS hydride epitaxy (MOSHE) method. Photocurrent multiplication factors, which varied from 1 to 18–25 in the range of reverse bias voltages of U = 8–14 V, were calculated based on the studied current–voltage characteristics of avalanche elements in the matrices.

RFID AC Current Sensing Technique

The mechanism is described by which a passive UHF RFID tag coupled with a tuning circuit is integrated with a current transformer for sensing ac current in an electrical wire for smart power monitoring of individual appliances. A capacitance change in the tuning circuit results from a reverse bias voltage from the current transformer. The tuning circuit reactance is detected by a capacitance sensing RFID tag and the value is transmitted as a 5–bit sensor code which is directly related to the ac current drawn by an electrical load. The passive tag harvests energy and offers an innovative solution for energy management in future smart homes and for industry 4.0. As well as indicating current level, the technique can also be used to detect the ON and OFF state of an electrical device and is demonstrated to work for a rapidly switching load. The sensor is tuned for EPC Class 1 Generation 2 UHF RFID readers at 868 MHz.

Color Determination from a Single Broadband Organic Photodiode

AbstractEstablishing the color of incident light is essential for many applications, such as machine vision, but generally requires either a dispersive component or multiple spectrally selective photodetectors. In contrast, here an incident spectrum is parametrized using a single broadband organic photodiode (OPD). This is achieved by exploiting the incident wavelength dependence of charge extraction caused by optically induced trap states in a metal oxide electron extraction layer, which results in an atypical spectral dependence of the reverse bias photocurrent density vs voltage (J–V) characteristics. Such dependence is augmented by confining the active layer within an optical microcavity to influence the light absorption profile and thus metal oxide trap state density. The average wavelength of an (approximately normally distributed) incident spectrum is then calculated to within ≈5 nm by algorithmically minimizing the difference between a measured J–V curve and one determined from the overlap integral of a trial spectrum with previously acquired voltage bias dependent external quantum efficiency (EQE) spectra.