Reverse Bias Conditions Research Articles

Expeditiously Crystallized Pure Orthorhombic-Hf0.5Zr0.5O2 for Negative Capacitance Field Effect Transistors.

Ultralow-power logic devices are next-generation electronics in which their maximum efficacies are realized at minimum input power expenses. The integration of ferroelectric negative capacitors in the regular gate stacks of two-dimensional field-effect transistors addresses two intriguing challenges in today's electronics; short channel effects and high operating voltages. The complementary-metal-oxide-semiconductor-compatible Hf0.5Zr0.5O2 (HZO) is an excellent ferroelectric material crystallized in a noncentrosymmetric o-phase. The present work is the first to utilize pulsed laser deposition (PLD)-grown phase-pure ferroelectric HZO to achieve steep slope negative capacitance (NC) in field effect transistors (FETs). A dual-step growth strategy is designed to achieve phase-pure orthorhombic HZO on silicon and other conducting substrates. The room-temperature PLD-grown amorphous HZO is allowed to crystallize using rapid thermal annealing at 600 °C. The polycrystalline orthorhombic HZO is further integrated with atomic layer deposition-grown HfO2 to achieve a stable NC transition. The stack is further integrated into the molybdenum disulfide channel to achieve steep switching and a hysteresis-free operation of the resulting FETs. The subthreshold swings of the FETs are 20.42 and 26.16 mV/dec in forward and reverse bias conditions, respectively.

(Invited) Understanding the Electroluminescence Signature of High-Voltage Vertical GaN Pin Diodes with Different Edge Termination Designs

GaN has superior properties, such as a wide band gap and high critical electric field that make it promising material for future power semiconductor devices. Edge termination for GaN power devices remains a subject of significant interest. In this work, different edge termination designs were systematically evaluated and compared by utilizing broadband electroluminescence technique under various reverse bias conditions. Edge termination is a crucial step in power devices fabrication process, using nitrogen implant is a common step in GaN PiN diode. In this work, Nitrogen ion implantation was used to form junction termination extension (JTE) and Guard Rings (GR). A full 2” wafer was fabricated in a foundry process to build a high current 1.2kV class GaN vertical diodes on non-homogenous GaN substrate. In silicon power devices, a smooth tapered implanted doping profiles are often achieved through a controlled diffusion of the implanted dopant island during activation. Activation and diffusion of acceptor dopants via ion implantation is neither well controlled nor understood in GaN. In this work, based JTE terminations, GR termination and a combination of both were compared. We are comparing several devices on the same wafer type and same fabrication process but with different edge termination designs; and spatially resolving their spectrum, by utilizing the electroluminescence mapping technique to acquire a series of broadband images under high voltage reverse bias. There is a clear difference in the electroluminescence signature. This is the first time we show the impact of edge termination on the evolution of these defects and the transport path of the leakage current. The leakage current, and hence the electroluminescence signature is changing as well with the termination design. All the termination and guard ring designs were based on Nitrogen implant. The nitrogen implant doses and energy are chosen to create enough damage in the p-type region. Stress testing is in-progress to evaluate the impact of these defects on failure mechanisms. JTE only design show a leakage current as a bright ring on the outer perimeter of the device active region closer to trench isolation while a GR only design brings the leakage current near the anode. A combination of both termination designs results in scattered leakage points on the outer perimeter of the device. Simulation results of the filed profiles of the different structures and hyperspectral EL and Raman spectroscopy are in progress along with temperature stressing to understand the nitrogen diffusion mechanisms in GaN. This study will have an impact on the future of GaN power devices and mature its process to compete with SiC technology. Figure 1

Analysis of the post-stress recovery of reverse leakage current in GaN HEMTs

The recovery of high reverse gate leakage current in AlGaN/GaN HEMTs has been analyzed in this study. To demonstrate the recovery after a thermal stress for large time periods (8–12 h), two mechanisms: phonon assisted tunnelling (PAT) and trap assisted tunnelling (TAT) have been utilized. Charge-based analytical models from literature have been used to match experimental leakage currents in reverse bias conditions. The degradation in the devices has been activated through thermal stress and the effect of high electric field induced inverse piezo electric effect has been eliminated. PAT component shows dominance in higher temperature regime (T > 500 K) and the slow recovery at 300 K with characteristic τ values around 5–13 h has been attributed to the TAT component through a deep trap level within the AlGaN barrier.

Characterization of predictable quantum efficient detector in terms of optical non-linearity in the visible to near-infrared range

The characteristics of a predictable quantum efficient detector (PQED) in terms of optical non-linearity in the visible to near-infrared range were investigated under zero-bias and reverse-bias voltage conditions. In the zero-bias condition, linear behavior was observed in the wavelength from 405 nm to 1060 nm in the photocurrent range of 1 nA to 10 μA, and saturation occurred for photocurrents over 10 μA for all wavelengths. In the reverse-bias voltage of 10 V, the linear behavior was observed in the photocurrent range of 64 nA to 1 mA except for the wavelength of 1060 nm, and the saturation photocurrent increased up to 1 mA. The supralinearity value at 1060 nm increased sharply from the photocurrent of 100 μA, and its maximum value reached up to 0.34% at the photocurrent of 1 mA because of the back surface recombination and the longer absorption length. The spectral linearity results of the PQED help us to understand the charge-carrier loss mechanism in the PQED, and would lead to more accurate optical measurement with it.

Utilization of asymmetrical electron transport as strategy for modelling and design of efficient single molecule diodes: A DFT investigation

Present study investigates two organic molecular systems, p − Sexiphenyl − σ − TCNQ and p − Sexiphenyl − σ − NTCDA, for possible use as single molecule diodes based on the Aviram and Ratner concept of D − σ − A model. Quantum chemical simulations were performed under the density functional theory (DFT) approach, using B3LYP functional and 6 − 31G(d,p) basis set. Calculated values of HOMO − LUMO gap, dipole moment and natural charges have been used for analysis. Results have been analyzed for both systems at different values of applied electric fields in both directions along the molecular axis. The results show that, HOMO − LUMO gap in forward biased condition (D to A direction of electric field) shrinks on increasing the electric field strength, whereas, in the reverse biased condition (A to D direction of electric field) the HOMO − LUMO gap increases until the breakdown condition is achieved. If the electric field strength is further increased in reverse bias condition, behaviour similar to avalanche breakdown is observed.

Performance of five commercial bipolar membranes under forward and reverse bias conditions for acid-base flow battery applications

The list of bipolar membrane (BPM) applications is constantly growing, thanks to the ability of BPMs to enhance water dissociation at low voltage losses and maintain a stable pH gradient across the membrane. Despite several BPMs are available in the market, a comprehensive characterization of membrane properties is still lacking, as BPMs are typically tested only via a steady-state polarization sweep under reverse bias. This work aims to present a systematic characterization of five commercial bipolar membranes using different techniques, investigating BPMs in terms of material and electrochemical properties, as well as overall performance in an acid-base flow battery system (i.e., both under reverse and forward bias). In particular, when testing BPMs in a single-cell acid-base flow battery, we reached round-trip efficiencies up to 65% using current densities of 60 A/m2 during discharge and 240 A/m2 during charge. Moreover, this work shows how further research is needed to lower the proton leakage through the anion exchange layer and electrical resistance, to improve the performance of BPMs for acid-base flow battery and other energy applications.

Light Detection Functionality of Photonic-Crystal Lasers

The photonic-crystal surface-emitting laser is a new-generation semiconductor laser capable of emitting a high-power, high-quality (i.e., high-brightness) beam, as well as on-chip two-dimensional beam steering, lasing in various wavelength regimes, and on-chip ultra-short self-pulsation, owing to their freedom of light-matter control. Here we introduce light detection as a new functionality, wherein the photonic-crystal laser is operated under reverse-bias conditions. We find that the photonic-crystal laser operated under reverse-bias conditions has a very high shunt resistance and a low dark current, which are essential qualities to achieve high detectivity. In addition, high responsivity is achieved by utilizing proper band-edge-modes and Q-matching conditions for resonant light absorption. Furthermore, by employing photonic-crystal lasers as the detector as well as the laser source, a direct time-of-flight distance measurement is successfully demonstrated.

Dynamics of charge carriers and photoresponse of TPD/n-Si hybrid structure for visible-blind UV self-biased photodetection applications

Herein, we represent the fabrication of self-biased visible-blind UV photodetector based on thermally deposited N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) film over n-type silicon substrate giving rise to the structure Au/TPD/n-Si/Al heterojunction. The microelectronic parameters of the fabricated heterojunction Au/TPD/n-Si/Al as well as the charge carriers' transport mechanisms in forward and reverse bias conditions are analyzed and interpreted in detail under the dark conditions and the influence of temperature. The manufactured photodetector showed a significant response to UV illumination with high photocurrents and noticeable values of open-circuit voltage. The fabricated UV photodetector under self-biasing and illumination intensity (100 mW/cm2) records values of responsivity, specific detectivity, linear dynamic range, signal to noise ratio, the response time, and ON/OFF ratio equals 147 mA/W, 6.4 × 1010 Jones, 58.69 dB, 945.5, 82/80 ms, and 861.98, respectively. This high, stable, and fast performance of the fabricated sensor suggest this architecture as an efficient integrated platform for self-biased UV photodetection.

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.

Near-infrared detection in Si/InP core-shell radial heterojunction nanowire arrays

We have explored the photodetection properties of a core-shell nanowire (NW) heterojunction based device consisting of p-Si/n-InP with an aim to provide an alternative to Si based photodetector by integrating a III-V material, viz. InP with silicon. The core is p-Si NWs, prepared by metal assisted chemical etching of p-type Si (100) substrate at room temperature using Ag nanoparticles, whereas n-type InP shells were deposited by metal organic chemical vapor deposition. The current-voltage characteristics of the device resemble that of a p-n junction with good rectification ratio in the dark, and provides photoresponse under visible and near-infrared (NIR) spectral region at low reverse bias condition. In the NIR regime, it shows an on/off ratio of 23 with a rise and fall time of 387 ms and 424 ms, respectively, at a reverse bias voltage of 2 V. The device exhibits a peak responsivity and detectivity of 2.749 A/W and 5.52 × 1011 Jones, respectively, at 920 nm under the same reverse bias voltage. Thus p-SiNW/n-InP core-shell based device could have the potential to be developed as an optoelectronic device beyond the traditional p-n junction exploiting its radial heterojunction based structure.

Bipolar Light‐Addressable Potentiometric Sensor Based on Fullerene Photosensitive Layer

AbstractLight‐addressable potentiometric sensor (LAPS) is highly attractive in many sectors, including human disease detection, drug screening, and environmental monitoring. Currently, classical LAPS chips adopt inorganic semiconductors, such as silicon, as the photosensitive layer. Organic semiconductors can provide the next generation of the photosensitive layer because of their high absorption efficiency, large structural variability, eco‐friendliness, and bendability. However, no promising organic materials have been reported so far for the construction of LAPS chips. Here, the authors demonstrate the potential of fullerene (C60), a π‐conjugated carbon molecule with high n‐type conduction, as a candidate material for the photosensitive layer of LAPS. They report on a peculiar bipolar photo‐response under both reverse and forward biased conditions for C60‐based LAPS. An oxygen‐trap‐induced space‐charge mechanism is proposed to explain the unique bipolar photo‐response phenomenon. The proposed C60‐based LAPS exhibits an excellent pH sensitivity of 150 mV/pH as well as a high spatial resolution of 3.8 µm. The authors anticipate that these results will spark interest in this field and enable the replacement of the inorganic‐semiconductor photosensitive layer by organic semiconductor materials for the construction of high‐performance LAPS.

Solution-processed near-infrared Cu(In,Ga)(S,Se)2 photodetectors with enhanced chalcopyrite crystallization and bandgap grading structure via potassium incorporation

Although solution-processed Cu(In,Ga)(S,Se)2 (CIGS) absorber layers can potentially enable the low-cost and large-area production of highly stable electronic devices, they have rarely been applied in photodetector applications. In this work, we present a near-infrared photodetector functioning at 980 nm based on solution-processed CIGS with a potassium-induced bandgap grading structure and chalcopyrite grain growth. The incorporation of potassium in the CIGS film promotes Se uptake in the bulk of the film during the chalcogenization process, resulting in a bandgap grading structure with a wide space charge region that allows improved light absorption in the near-infrared region and charge carrier separation. Also, increasing the Se penetration in the potassium-incorporated CIGS film leads to the enhancement of chalcopyrite crystalline grain growth, increasing charge carrier mobility. Under the reverse bias condition, associated with hole tunneling from the ZnO interlayer, the increasing carrier mobility of potassium-incorporated CIGS photodetector improved photosensitivity and particularly external quantum efficiency more than 100% at low light intensity. The responsivity and detectivity of the potassium-incorporated CIGS photodetector reach 1.87 A W−1 and 6.45 times 1010 Jones, respectively, and the − 3 dB bandwidth of the device extends to 10.5 kHz under 980 nm near-infrared light.

Modified expressions of field and thermionic-field emission for Schottky barrier diodes in the reverse regime

In this theoretical work, the author has modified the current-voltage relationship of the field and thermionic–field emission models developed by Padovani and Stratton for the Schottky barrier diodes in the reverse bias conditions with account of the image force correction. Considered in this approach has been the shape of Schottky barrier as trapezoidal. The obtained results show a good agreement between current densities calculated within the framework of these developed models and those calculated using the general model.

Diamond Schottky barrier diodes fabricated on sapphire-based freestanding heteroepitaxial diamond substrate

In this study, diamond Schottky barrier diodes (SBDs) fabricated on a sapphire-based heteroepitaxial diamond substrate were demonstrated. For commercializing diamond-based power electronics, a large-sized heteroepitaxial diamond substrate is essential. Sapphire is one of the most promising candidates among the diamond heteroepitaxial substrates because it can be produced on a large scale and its thermal expansion coefficient is similar to that of diamond, compared to that of any other non-diamond hetero substrate. The current-voltage characteristics of heteroepitaxial diamond SBDs grown under different growth rates were analyzed, and good rectification properties of SBDs were observed at the device grown with low growth rate. The ideality factor was 1.4, and the maximum breakdown field was approximately 1.1 MV/cm. The value of built-in potential derived from the capacitance-voltage characteristics was in good agreement with the approximated barrier heights. Some ball-shaped features on the SBD along the threading dislocation were directly observed after performing the breakdown test under reverse bias condition using transmission electron microscope (TEM). Threading dislocation which induces breakdown or large leakage current under reverse bias in diamond SBD was clarified and this will lead the research direction of a heteroepitaxial diamond electronic device. Prime novelty statementsRecently, the diamond SBD grown on large-size heteroepitaxial diamond substrates becoming alternative to conventional high temperature high pressure (HPHT) diamond-based diamond SBD. In this study, diamond SBD grown on sapphire-based freestanding heteroepitaxial diamond substrate was successfully demonstrated. The sapphire substrate is one of the most promising material as substrate for heteroepitaxial diamond which is low cost and large sized. The heteroepitaxial diamond SBD structures with different growth rate were grown using microwave plasma CVD (MPCVD) and its structural properties were characterized. After device fabrication process, the detailed analysis of electrical properties of SBD were carried out. The direct observation of breakdown and leakage current features on SBD was obtained before and after electrical test under reverse bias condition.

Band offsets, dielectric dispersion and some applications of CdSe/GeO2 heterojunctions

Herein, the formation, structural, morphological, compositional, optical, dielectric, photoelectrical and electrical properties of the CdSe/GeO2 heterojunctions are explored. While the surface displayed formation of deficient GeO, the bulk of the films exhibited correct stoichiometry of GeO2 and CdSe. It is found that stacking of GeO2 onto CdSe enhances the crystallinity of CdSe by reducing the defects concentrations. It blue shifts the energy band gap of CdSe from 1.74 eV to 2.60 eV. The stacked layers of CdSe/GeO2 displayed conduction and valence band offsets of 2.34 eV and 1.23 eV, respectively. In addition, the Drude-Lorentz model analyses have shown that the coating of GeO2 onto CdSe, highly increases the drift mobility of charge carriers and tunes the plasmon frequency making it more appropriate for optoelectronic device applications. When exposed to light irradiation, an illumination intensity dependent photosensitivity is observed. The photoconduction mechanism is governed by the sublinear recombination with exponential trap distribution. Moreover, the capacitance –voltage characteristics of the device revealed metal-oxide-semiconductor field effect transistors (MOSFET) characteristics. The built in potential for this device under reverse biasing conditions reached 4.74 eV.

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.

Dual-functional quantum-dots light emitting diodes based on solution processable vanadium oxide hole injection layer

Dual-functional quantum-dots light emitting diodes (QLEDs) have been fabricated using solution processable vanadium oxide (V2O5) hole injection layer to control the carrier transport behavior. The device shows selectable functionalities of photo-detecting and light-emitting behaviors according to the different operating voltage conditions. The device emitted a bright green light at the wavelength of 536 nm, and with the maximum luminance of 31,668 cd/m2 in a forward bias of 8.6 V. Meanwhile, the device could operate as a photodetector in a reverse bias condition. The device was perfectly turned off in a reverse bias, while an increase of photocurrent was observed during the illumination of 520 nm wavelength light on the device. The interfacial electronic structure of the device prepared with different concentration V2O5 solution was measured in detail using x-ray and ultraviolet photoelectron spectroscopy. Both the highest occupied molecular orbital and the gap state levels were moved closer to the Fermi level, according to increase the concentration of V2O5 solution. The change of gap state position enables to fabricate a dual-functional QLEDs. Therefore, the device could operate both as a photodetector and as a light-emitting diode with different applied bias. The result suggests that QLEDs can be used as a photosensor and as a light-emitting diode for the future display industry.

A CMOS Rectifier Employing Body Biasing Scheme for RF Energy Harvesting

This paper presents a CMOS rectifier for RF energy harvesting. The structure of the proposed design is based on a modified cross-coupled architecture. It employs an adaptive body biasing technique to lower the transistor threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) when the PMOS is ON. This would increase the conduction current. Moreover, this technique increases V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> when the PMOS is OFF. This would minimize the current flowing in the reverse bias condition. The proposed design is simulated using 0.18 μm TSMC CMOS technology under various loading conditions and an input frequency of 953 MHz. A peak power conversion efficiency (PCE) of 78.2% is achieved at an input power of -27.5 dBm and a 100 kΩ load.

Memristiv effect on W/Ti/p-Si structure: Aging phenomena and one of the origin of barrier inhomogeneity

Memristor as claimed to be fourth two terminal passive devices in electronics. Experimental realization memristor by HP research group is getting much more attention due to its potential applications. However, in reality this device with its unique properties always exist in MOS, MIS or even MS junctions. But its visibility has a dependence to oxide or interface thickness with mobile ions. As reported in this study, current–voltage (I-V) relation of W/Ti/p-Si continuously modified by the forward bias current. Departure form linear relation between ln(I)-V commonly analyzed with barrier inhomogeneity assumption. The appearance of barrier inhomogeneity for MS junction reported to be one of the reasons for non-ideal ln(I)-V relation. Investigation in this study shows that total charge Q(t) controlled by voltage sweep rate effecting forward ln(I)-V relation. If this situation exists, calculated barrier heights and ideality factors are not true and a pure barrier inhomogeneity approximation may not be applicable. However, under the reverse bias condition, the total charge during entire measurement is so small which it’s effect negligible over I-V relation as observed. The one of the solution is the use Missous-Rhoderick method for finding Schottky diode parameters or creating current stress over MS junction which saturates mobile ion drift. Voltage sweep rate during I-V measurement and hence total charge, affecting current transport and in parallel appearance of hysteresis loop indicate interface layer which behave as a memristor.

Fabrication of A Diode-based Salt Solution Sensor

High blood pressure/hypertension is a severe medical issue among Malaysians that could be reduced by monitoring our salt/sodium intake. One way is to use intraoral salt sensor; this in-mouth method however may cause discomfort and adopts complex and costly fabrication processes. Hence, an external and reusable electronic device, that could be used as a “sweat-sensor”, is preferred in detecting the sodium intake of the body. In this study, a potentiometric diode-based salt solution sensor was designed and fabricated in order to detect different salt solution concentrations with applied external voltage. A p-n junction diode sensor was successfully designed and fabricated using four consecutive techniques; thermal wet oxidation, photolithography, thermal diffusion and metallization. The average sheet resistance and resistivity of the diode sensor were measured to be 3.50 x 105 ± 0.66 Ω⁄sq and 3.05 ± 0.5 Ωcm respectively. This sensor showed ideal I-V diode characteristics with a knee voltage of 11.5V in forward bias condition and breakdown voltage of -4 V in reverse bias condition. For salt concentration detection, the sensor was able to detect salt concentration changes with respect to current flow, up to 45 mg/mL.