Search

This paper presents a comprehensive investigation into the DC analog and AC microwave performance of a state-of-the-art T-gate double barrier AlGaN/AlInGaN/GaN MOSHEMT (Metal Oxide Semiconductor High Electron Mobility Transistor) implemented on a 4H-SiC substrate. The study involves meticulous numerical simulations and an extensive comparison with a single barrier design, utilizing the TCAD-Silvaco software. The observed disparity in performance can be attributed to the utilization of double barrier technology, which enhances electron confinement and current density by augmenting the polarization-induced charge during high-frequency operations. Remarkably, when compared to the single barrier design, the double barrier MOSHEMT exhibits a notable 15% increase in drain current, a 5% increase in transconductance, and an elevated breakdown voltage (VBR) of 140 V in E-mode operation. Furthermore, the radio frequency analysis of the double barrier device showcases exceptional performance, setting new records with a maximum oscillation frequency (fmax) of 1.148 THz and a gain cutoff frequency (ft) of 891 GHz. These impressive results obtained through deck-simulation affirm the immense potential of the proposed double barrier AlGaN/AlInGaN/GaN MOSHEMT for future applications in high-power and terahertz frequency domains.

We prepare a symmetrical double barrier structure of Mo/AlN/Mo/AlN/Mo by using the reactive magnetron sputtering on a sapphire substrate and examine its resonant tunneling effect. Characterizations of multilayers demonstrate that the AlN (0002) aligns well along the Mo (110). Direct current-voltage (DC I–V) test finds significant negative differential resistance at room temperature around 0.7 and 0.9 V carrier energy and with peak-to-valley current ratios of about 1.1 and 1.2. The simulation using conventional transfer matrix method suggests good consistence between the designed structure, the quantized energy level and the switching voltage. The large signal DC model also fits the experimental I–V properties. Our work provides a new type of resonant tunneling device in room temperature. • Constructing novel structures for resonant tunneling devices. • The NDR phenomenon at room temperature was obtained. • Preparing devices beyond the shortcomings of magnetron sputtering. • Simultaneous use of physical and electrical models to explain mechanisms. • This work provided a new type of resonant tunneling device. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to show the existence results for adapted solutions of infinite horizon doubly reflected backward stochastic differential equations with jumps. These results are applied to get the existence of an optimal impulse control strategy for an infinite horizon impulse control problem. Design/methodology/approach – The main methods used to achieve the objectives of this paper are the properties of the Snell envelope which reduce the problem of impulse control to the existence of a pair of right continuous left limited processes. Some numerical results are provided to show the main results. Findings – In this paper, the authors found the existence of a couple of processes via the notion of doubly reflected backward stochastic differential equation to prove the existence of an optimal strategy which maximizes the expected profit of a firm in an infinite horizon problem with jumps. Originality/value – In this paper, the authors found new tools in stochastic analysis. They extend to the infinite horizon case the results of doubly reflected backward stochastic differential equations with jumps. Then the authors prove the existence of processes using Envelope Snell to find an optimal strategy of our control problem.

Direct manufacturing of two-dimensional material-based double barrier (DB) tunnel junctions, based on a lithography-free approach was developed. Graphene/h-BN/Graphene/h-BN/Graphene devices were deposited on Si/SiO2 substrates by employing a plasma enhanced chemical vapor deposition technique in a sequential manner. DB tunneling junctions with varying barrier widths (by varying the thickness of the second graphene layer) were studied. Samples were characterized using Raman, Atomic Force Microscopy and X-ray photoemission spectroscopy. The I–V characteristics of tunneling current showed resonant tunneling behavior at room temperature with a negative differential conductance. The behavior could be explained with quantum mechanical double barrier tunneling model in which analytic solutions to Schrödinger's equation were obtained in each region of the system. Resonances in transmission probability coefficient for varying barrier widths were evaluated and compared with the experimental results. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to show the existence results for adapted solutions of infinite horizon doubly reflected backward stochastic differential equations with jumps. These results are applied to get the existence of an optimal impulse control strategy for an infinite horizon impulse control problem. Design/methodology/approach - The main methods used to achieve the objectives of this paper are the properties of the Snell envelope which reduce the problem of impulse control to the existence of a pair of right continuous left limited processes. Some numerical results are provided to show the main results. Findings - In this paper, the authors found the existence of a couple of processes via the notion of doubly reflected backward stochastic differential equation to prove the existence of an optimal strategy which maximizes the expected profit of a firm in an infinite horizon problem with jumps. Originality/value - In this paper, the authors found new tools in stochastic analysis. They extend to the infinite horizon case the results of doubly reflected backward stochastic differential equations with jumps. Then the authors prove the existence of processes using Envelope Snell to find an optimal strategy of our control problem. [ABSTRACT FROM AUTHOR]

A novel lattice matched double barrier Al0.72In0.16Ga0.12N/Al0.18In0.04Ga0.78N/GaN normally-off high electron mobility transistor (HEMT) is designed and simulated by solving a set of thermodynamic transport equations. Using the experimentally calibrated physical models with bearing mobility degradation by surface roughness in account, the recess gate and double barrier of the proposed device achieves a maximum drain current density (ID,max) of 1149 mA/mm and a maximum transconductance (gD,max) of 358 mS/mm with a positive threshold voltage (Vth) of 0.2 V. The small polarization charge of first barrier is responsible for positive Vth. IDS,max in the double barrier HEMT at high gate bias condition is due to injection of electrons from upper 2DEG which is almost impossible at lower gate voltage because of insufficient energy to cross the barrier. The injection of electrons is further supported by the second peak in the gm curve at low gate bias VG = 1V. The outcome of this study suggests that the proposed device will be beneficial for high-frequency and high-power electronic applications.

This paper aims to study the asymptotic behavior of double barrier American-style put option prices under an uncertain volatility model, which degenerates to a single point. We give an approximation of the double barrier American-style option prices with a small volatility interval, expressed by the Black–Scholes–Barenblatt equation. Then, we propose a novel representation for the early exercise boundary of American-style double barrier options in terms of the optimal stopping boundary of a single barrier contract. [ABSTRACT FROM AUTHOR]

The paper discusses the chiral tunneling of charge carriers through double barrier structure in twisted graphene bilayer. The theoretical analysis investigates the transmission probability for various system parameters under both symmetric and asymmetric barrier conditions. The results reveal that the transmission probability of quasiparticles in the K cone is mirror symmetric to that of K θ cone about φ = 0. Furthermore, the study shows that the transmission changes gradually from perfect transmission to perfect reflection in the normal direction by increasing the incident energy and the barrier height, which is different from the case of monolayer and AB-stacked bilayer graphene. It is also found that the double barrier structure remains, only in certain cases, perfectly transparent for normal or near-normal incidence. The chiral nature of the quasiparticles in graphene causes the tunneling to be highly dependent on the direction and also on the double barrier structure. Interestingly, this characteristic provides additional parameter that allows us to tune the electronic properties of the twisted graphene bilayer. Additionally, we found that the transmission exhibits some sharp resonance peaks, the number and amplitude of which depend on the system parameters. Our results provide a better understanding of chiral tunneling in twisted graphene bilayers through double barrier structures, which may thus offer efficient tools to control the transport properties in future graphene-based nanodevices like transistors and photodetectors. • Chiral Tunneling in twisted graphene bilayer. • Transmission through double barrier structure. • The transmission in the K cone is mirror symmetric to that of K θ cone about ϕ = 0. • The double barrier structure remains perfectly transparent for normal or near-normal incidence in certain cases. • The periodicity of transmission with U 2 and U 4 is not affected by d 2 − 1. [ABSTRACT FROM AUTHOR]

Vacuum windows are an essential part of any radio frequency (RF) system which launches/couples RF power from an atmospheric to a vacuum environment. This paper describes the RF design of a double barrier ceramic coaxial vacuum window. Alumina 99.5% pure is considered as ceramic barrier material while inner and outer conductors are oxygen-free copper. As the initial design approach the thickness, slope, depth of ceramic in the conductor is varied and the performance of the window is studied. The design is optimised to achieve the best insertion loss, return loss response for operating frequency range up to 65MHz. [ABSTRACT FROM AUTHOR]

In this paper, we apply an improved version of Monte Carlo methods to pricing barrier options. This kind of options may match with risk hedging needs more closely than standard options. Barrier options behave like a plain vanilla option with one exception. A zero payoff may occur before expiry, if the option ceases to exist; accordingly, barrier options are cheaper than similar standard vanilla options. We apply a new Monte Carlo method to compute the prices of single and double barrier options written on stocks. The basic idea of the new method is to use uniformly distributed random numbers and an exit probability in order to perform a robust estimation of the first time the stock price hits the barrier. Using uniformly distributed random numbers decreases the estimation of first hitting time error in comparison with standard Monte Carlo or similar methods. It is numerically shown that the answer of our method is closer to the exact value and the first hitting time error is reduced.

Abstract. The application of double barrier (DB) structure in p-i-n amorphous silicon (a-Si) device was studied. The theoretical study was done to obtain device parameters such as tunneling probability and current density. The tunneling probability was calculated by employing the Schroedinger equation, WKB approximation and Green function. Width of potential well, width and height of barrier were varied to obtain the highest tunneling probability value. The current density was contributed by diffusion, and tunneling current densities. It was found that current density had a peak of 3950 A/m2 at 0.56 volt forward bias. Furthermore, the fabrication of p-i-n a-Si device with double barrier structure was successfully carried out. To realize the double barrier structure, optimization of optical band gap of barrier a-SiC:H was done by varying ratio of CH4 to [CH4+SiH4]. The fabrication of p-i-n a-Si device was then done by using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique with a structure of glass substrate/TCO/p-a-Si:H (2.15 eV;140Ã…)/i-a-Si:H (1.81 eV;1800 Ã…)/barrier a-SiC:H (2.36 eV;45 Ã…)/potential well i-a-Si:H (1/81 eV; 30 Ã…)/barrier a-SiC:H (2.36 eV; 45 Ã…)/n-a-Si:H (1.81 eV;180 Ã…)/Al. The I-V characteristic of the device showed a peak current calue at 0.55 forward bias. Simulasi dan Fabrikasi Struktur Double Barrier pada Divais Amorphous Silicon Sari. Aplikasi struktur double barrier (DB) pada divais amorphous silicon (a-Si) telah dilakukan untuk memperoleh beberapa parameter divais seperti probabilitas tunneling dan rapat arus. Probabilitas tunneling dihitung dengan menerapkan persamaan Schroedinger, pendekatan WKB dan fungsi Green. Lebar sumur potensial, lebar dan tinggi barrier telah divariasikan untuk memperoleh harga probabilitas tunneling yang maksimum. Rapat arus total dari divais dalam perhitungan ini merupakan jumlah dari rapat arus difusi dan rapat arus tunneling. Diperoleh bahwa rapat arus total memiliki nilai maksimum sebesar 3950 A/m2 pada tegangan bias maju 0,56 volt. Selanjutnya, telah berhasil juga difabrikasi divais p-i-n a-Si dengan struktur double barrier. Didapatkan bahwa karakteristik I-V dari divais menunjukkan adanya puncak rapat arus pada tegangan bias maju 0,55 volt. ihamidah@eudoramail.com

In this article, two general results are provided about the multidimensional Black–Scholes partial differential equation: its fundamental solution is derived, and it is shown how to turn it into the standard heat equation in whatever dimension. A fundamental connection is established between the multivariate normal distribution and the linear second order partial differential operator of parabolic type. These results allow to compute new closed form formulae for the valuation of multiasset options, with possible boundary crossing conditions, thus partially alleviating the « curse of dimensionality », at least in moderate dimension. [ABSTRACT FROM AUTHOR]

As the basic storage unit of spin transfer torque magnetic random-access memory (STT-MRAM), the perpendicular magnetic anisotropy (PMA) magnetic tunnel junction (MTJ) has been extensively studied in recent years. Lowering the critical switching current and improving the data retention are two crucial pathways to optimize the performance of STT-MRAM. However, the conventional MTJ can merely achieve both. In this paper, we present a physics-based compact model of Ta/CoFeB/MgO PMA double-barrier MTJ (DMTJ) with enhanced thermal stability recording structure. Combination of double-barrier and synthetic double-free layers can heighten the STT effect and enhance the thermal stability simultaneously. A larger STT switching efficiency, compared with conventional MTJ, can thus be realized. The modeling results show great agreement with experimental results. A 1-bit magnetic full adder (MFA) based on DMTJ, as a hybrid logic-in-memory circuit example, has been designed and simulated to validate its functionality. This SPICE-compatible compact model will be useful for high-performance hybrid MTJ/CMOS circuit and system designs. [ABSTRACT FROM AUTHOR]

In this study, we investigated and simulated the structure of a quantum well resonant tunneling (QWRT) transistor based on two barriers and a well in the middle. The barriers were formed of semiconductors with a higher bandgap and the well separating the barriers comprised a semimetal-like material with a very small bandgap, i.e., close to zero. The device was positioned on the oxide to exploit the benefits of SOI technology, e.g., improving leakage and the immunity of the device against environment effects. When the well thickness was a few nanometers, the electron-bound states appeared in the quantum well region. By tuning the voltage and work function of the top gate, the bound states moved in the potential well and the carriers were transferred through the well via the resonant tunneling phenomenon. Our simulations showed the step-like behavior of the output characteristics and the oscillatory quantum switching of the transfer characteristics for the proposed device. We also investigated the influence of the well thickness and gate voltage on the device characteristics, and we compared the optimal case with a theoretical analysis of a QWRT transistor based on a topological insulator. • Quantum well resonant tunneling (QWRT) transistor based on a topological insulator. • Counterpart QWRT conventional device simulated using ATLAS. • NEGF employed to consider tunneling, ballistic transport, and quantum confinement. • Transfer and output characteristics compared between two devices. • Impact of well thickness assessed on output conductance and I d –V d characteristics. [ABSTRACT FROM AUTHOR]

Abstract We study spin-dependent electron transport properties of two dimensional graphene double and triple barrier junctions via first-principles calculations. The double barrier junction consists of two graphene leads, a quantum well of zigzag graphene nanoribbon (ZGNR) in the center, and two vacuum barriers separating the ZGNR from the two leads. Resonant electron tunneling occurs when the energy bands of graphene and ZGNR are well aligned in energy and wavevector. Highly spin-polarized electron transmission arises in such junctions when the two edges of the center ZGNR are in the ferromagnetic configuration. The spin polarization of the electron transmission at the Fermi energy can be tuned by gate voltage. We further investigate the dependence of the electron transmission on the width of the ZGNR, effects on barrier height when replacing vacuum by h -BN, and the consequence of replacing a double barrier by a triple barrier. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and two different Al% (15% and 20%) in the bottom AlGaN barriers are designed. First of all, a double hump trans-conductance (gm)−gate voltage (VG) characteristic is observed in a recessed gate AlGaN/GaN MIS-HEMT with a 5 nm remaining bottom Al0.2Ga0.8N barrier under the gate region. Secondly, a physical model is proposed to explain this double channel characteristic by means of a formation of a top channel below the gate dielectric under a positive VG. Finally, the impacts of Al% content (15% and 20%) in the bottom AlGaN barrier and 5 nm/3 nm remaining bottom AlGaN barriers under the gate region are studied in detail, indicating that lowering Al% content in the bottom can increase the threshold voltage (VTH) toward an enhancement-mode characteristic.

This paper studies an infinite horizon impulse control problem where the costs are given by a diffusion process. The properties of the Snell envelope reduce this problem to the existence of a pair of continuous processes; this allows to establish an optimal impulse control solution. Finally, stability estimates and simulation results are provided. [ABSTRACT FROM AUTHOR]

In this paper, we apply an improved version of Monte Carlo methods to pricing barrier options. This kind of options may match with risk hedging needs more closely than standard options. Barrier options behave like a plain vanilla option with one exception. A zero payoff may occur before expiry, if the option ceases to exist; accordingly, barrier options are cheaper than similar standard vanilla options. We apply a new Monte Carlo method to compute the prices of single and double barrier options written on stocks. The basic idea of the new method is to use uniformly distributed random numbers and an exit probability in order to perform a robust estimation of the first time the stock price hits the barrier. Using uniformly distributed random numbers decreases the estimation of first hitting time error in comparison with standard Monte Carlo or similar methods. It is numerically shown that the answer of our method is closer to the exact value and the first hitting time error is reduced. [ABSTRACT FROM AUTHOR]

A new Monte Carlo method is presented to compute the prices of digital barrier options on stocks. The main idea of the new approach is to use an exceedance probability and uniformly distributed random numbers in order to efficiently estimate the first hitting time of barriers. It is numerically shown that the answer of this method is closer to the exact value and the first hitting time error of the modified Monte Carlo method decreases much faster than of the standard Monte Carlo methods. [ABSTRACT FROM AUTHOR]