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A novel lattice matched double barrier Al 0.72 In 0.16 Ga 0.12 N/Al 0.18 In 0.04 Ga 0.78 N/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 ( $I_{D,max}$ ) of 1149 mA/mm and a maximum transconductance ( $g_{m,max}$ ) of 358 mS/mm with a positive threshold voltage ( $V_{th}$ ) of 0.2 V. The small polarization charge of first barrier is responsible for positive $V_{th}$ . $I_{DS,max}$ 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 $\text{g}_{m}$ curve at low gate bias $V_{G} = 1\text{V}$ . The outcome of this study suggests that the proposed device will be beneficial for high-frequency and high-power electronic applications.

The hot carrier cell (HCSCs) is a promising advanced photovoltaic concept. It aims to minimize major losses in p-n junction solar cells and is predicted to have energy conversion efficiency over 65% at one sun. Energy selective contacts (ESCs) is a critical component of the HCSC. In this paper, potential of ESCs based on quantum dot and quantum well double barrier resonant tunneling structures is presented. Results of I-V measurements these show negative differential resistance (NDR) characteristics both at low temperature and room temperature, thus indicating that these structures can be suitable for ESC application.

Using the model of rectangular potential and smooth position-dependent electron effective mass, which is a linear function of coordinate in near-interface regions between wells and barriers of open double-barrier resonant tunneling nano-structure, the solutions of Schrodinger equation are obtained and transmitting coefficient of the structure is analytically calculated. The influence of the sizes of inner and outer near-interface regions on transmitting coefficient of the structure is investigated. The comparative analysis of resonance energies and resonance widths of sub-barrier electron quasi-stationary states as functions of these sizes is performed. It is shown that the relative differences of resonance energies and resonance widths of the same state of electron in the model of linearly-dependent effective mass and simplified abrupt one do not exceed 1% and 5%, respectively, in physically correct interval of the sizes of outer and inner near-interface regions.

This paper details the design of an integrate & fire (I & F) neuron ASIC and its integration with a double barrier memristor device. The memristor has a non-volatile analog memory characteristic which changes with time and voltage. The neuron ASIC is designed to interact with the memristor by integrating its current and firing when a certain threshold is reached. The resulting spikes increase the memristor's conductance and consequently the firing rate of neuron increases. Together, the ASIC and the memristor mimics neuromorphic learning on hardware. The ASIC has been fabricated in AMS 350nm process.

With the shrinking of complementary metal oxide semiconductor (CMOS) technology size, the considerable power consumption on logic and memory circuit system has been becoming an unavoidable bottleneck [1]. Spin transfer torque magnetoresistive memories (STT-MRAMs) are prime candidates for non-volatile memory applications. As the basic storage unit of STT-MRAM, magnetic tunnel junction (MTJ) has been extensively studied [2]–[4]. For instance, double-barrier MTJ (DMTJ), taking advantages of the enhancement of STT effect, significantly reduces the critical switching current $(\mathrm {I}_{C0})$ and switching duration $(\tau)$ [5]. MTJ with two CoFeB free layers (FLs) coupled by Ta layer can effectively improves the thermal stability $\left({ \Delta\mathrm {E}}\right)$ [6]. In this paper, we proposed an electrical modeling of DMTJ with CoFeB/Ta/CoFeB FLs (see Fig. 1 (a)). Compared with conventional MTJ, the propose DMTJ has superiorities in $\mathrm {I}_{C0}$, $\tau $, and $ \Delta\mathrm {E}$. It can replace MTJ to reduce the device size, improve the reliability of memory and lower the writing energy consumption. Furthermore, this model integrates the stochastic STT switching behavior, the temperature influence and the variation of the layers' thicknesses, which can deeply affect the reliability of hybrid CMOS/MTJ circuits. Fig. 1 (b) shows the principle block diagram of the integrated physical models. In the following, we explain some key blocks modeled in the Verilog-A code. For DMTJ, STTs generated by both the transmitted and reflected spin polarized electrons add together. This enhancement strongly decreases the $\mathrm {I}_{C0}$ and $\tau $, which can be expressed as\begin{align*} \mathrm {I}_{C0}= 2 \alpha \gamma \mathrm {e}\times (\mathrm {K}_{EFF} \times Volume)/ \mu _{B} \mathrm {g}_{DMTJ}(1) (1)\\ \tau =\left[{ \mathrm {C}+ In \left({ \pi ^{2} \Delta\mathrm {E}/ 4 }\right) }\right] \times (em/ 4 \mu _{B} \mathrm {g}_{DMT} \mathrm {J}) \times (\mathrm {I}_{write}- \mathrm {I}_{C0})^{-1}(2)\end{align*}

The considerable power consumption on logic and memory circuit system will be an unavoidable bottleneck with the shrinking of complementary metal oxide semiconductor (CMOS) technology size. One promising solution is to build non-volatile spintronic device, e.g. spin transfer torque magnetic random access memory (STT-MRAM). The basic storage unit of STT-MRAM, i.e. magnetic tunnel junction (MTJ), has thus been extensively studied. Double-barrier MTJ (DMTJ), as an optimized structure, enhances the STT effect with a second MgO barrier layer and reduces its critical switching current. In this paper, we present a physics-based compact model of CoFeB/MgO DMTJ with perpendicular magnetic anisotropy (PMA). The modeling results show a great agreement with experimental results. More efficient STT switching and similar magnetoresistance features compared with single-barrier MTJ (SMTJ) can be realized. Mixed circuits simulations have also been carried out to validate its functionality. This SPICE-compatible compact model will be useful for high-performance hybrid DMTJ/CMOS circuit and system designs.

The simulation is done for electron tunneling through the insulating layer of the magnetic tunnel junction with non-magnetic embedded nanoparticles (npMTJs). The distribution of the nanoparticles by size (DNPS) was important part of the solution for tunnel magnetoresistance (TMR) which was calculated on the basement of the double barrier tunneling model. It was found that theoretical agreement with experimental data can be influenced not only from DNPS but also due to different cases of the quantization. A few cases of the quantization related with a redistribution over quantum well (QW) states of the nanoparticles (NPs) (with diameter d) were considered (one of the possible DNPS and related TMR is shown in Fig. 1a and Fig. 1b).

We have a comparison between typical compact models of the double-barrier resonant-tunneling diodes from the point of view of limiting frequency performance. The techniques for the parameters estimating of the simplest diode model were considered. Compact model parameters were identified based on experimental data.

We demonstrate discrete resonant states in functionalized coupled waveguide arrays theoretically and experimentally. Our double barrier patterning of the coupling creates tunnel resonances in the transmitted intensity, which paves the way towards all optical control.

For asymmetric double-barrier resonant-tunneling structures with thin and high (delta) barriers, the dependences of the widths of resonance levels on amplitude of intensive high frequency electric field and peculiarities of electron transport near centers of the resonance levels have been investigated. It has been observed that the non-resonance scattering channel might be absolutely transparent and level widths might substantially exceed their low-signal values.

Summary form only given. Numerical modeling of the decay of quasi-stationary state in double-barrier structure and decay current oscillations are considered. Example of calculation for a model is presented.

By geometric randomization of the option maturity, we transform the n-steps backward recursion that arises in option pricing into an integral equation. The option price is then obtained solving n independent integral equations. This is accomplished by a quadrature procedure that transforms each integral equation in a linear system. Since the solution of each linear system is independent one of the other, we can exploit the potentiality of the grid architecture AGA1. We compare different quadrature methods of the integral equation with Monte Carlo simulation. Therefore we price options (such as plain vanilla, single and double barrier options) when the underlying evolves according to different exponential Levy processes.

Results are presented on device models for an optimisation of processes. In particular the double-barrier Al0.7Ga0.3As/GaAs heterostructure barrier varactor (HBV) designed using the commercial software Synopsys ISE- TCADreg, with accuracy higher than generally published. The design takes into account all the technological steps that are involved during the development of the HBV. The comparison with the measurements shows that the accuracy is higher than standard available models.

The negative differential resistance (NDR) characteristics of GaSb/AlSb/GaSb/AISb/lnAs double barrier structure were improved by incorporating an InAs blocking layer into the well region, i.e. GaSb/AlSb/InAs/GaSb/AlSb/InAs structure. The multiple NDR behaviors as well as high peak-to-valley ratios (PVRs) were observed with appropriate InAs well width. The three-band model was used to investigate the effect of the InAs well on the current-voltage characteristics of GaSb/AlSb/lnAs/GaSb/AISb/lnAs structures.

In this study, a triangular-barrier and a double-barrier structure were integrated to form a bi-directional switching device. In the structure center of the triangular barrier, a delta-doped (/spl delta/-doped) quantum well was inserted to enhance the carrier accumulation. Owing to the resonant tunneling through the double barrier and avalanche multiplication in the reverse-biased junction, N-shaped and S-shaped negative-differential-resistance (NDR) phenomena would occur in the current-voltage (I-V) characteristics under normal and reverse operation modes, respectively.

The TMR properties of epitaxial Fe(100)/MgO(100)/Fe(100)/MgO(100)/Fe(100) double barrier magnetic tunnel junctions (DMTJs) is reported. Both TMR and I-V characteristics were measured at room temperature using a dc four probe method. Single barrier MTJs (SMTJs) were used as references. A pseudo-spin-valve type TMR curve originated from the different magnetic switching fields (H/sub sw/) for the both top and bottom Fe layers (H/sub sw/ = 48 Oe) and for the middle Fe layer (H/sup sw/ = 14 Oe). Higher TMR ratios of up to 110% (average: 89%) compared with the SMTJ (average: 77%) are observed for the DMTJ although the magnitude of the TMR ratio for the DMTJ has been reported to be smaller than that for the SMTJs.

This article investigates the correlation between the optical and transport properties of zinc oxide-zinc magnesium oxide double barrier system by investigating the localization of the energy levels in the quantum well. Effective mass approach is used to investigate this system. The degree of localization of the levels in the quantum well is also examined with respect to the width of the ZnMgO barriers. The energy bands for ZnO/Zn/sub 0.8/Mg/sub 0.2/O structure is also studied.

In this paper, we compare the transport properties and temperature dependence of DBJs and single barrier junctions (SBJ). The results are discussed within a serial resistor model of the two single junctions. Ballistic and diffusive contributions to the tunneling current can be estimated, then.

A possibility for creating spin-polarized electron current sources with the help of a double-barrier resonant-tunneling semiconductor nanostructure composed of semimagnetic semiconductor (Zn/sub 1-x/Mn/sub x/Se) layers with different concentrations of manganese ions has been considered.

We have realized a series InAs/AlSb/GaSb tunneling structures in which both interband and intraband tunneling occur, dependent on injection energy. The baseline structure consists of a single InAs well with GaSb barriers which serve as quantum wells for interband tunneling and barriers for intraband tunneling. At low biases, interband tunneling occurs through a coupled double well structure in the GaSb valence bands. At higher biases, intraband tunneling occurs through the InAs quantum well. The addition of a thin AlSb barrier at different points in the structure changes both the strength and number of peaks in the I-V/G-V characteristics. >

A new Double Barrier Resonant Tunnel diode large-signal model suitable for SPICE simulation is presented in this paper. The model is based on the device I/V characteristic and can be successfully applied to simulating microwave applications such as oscillators, self-oscillating mixers, frequency multipliers, etc. The associated parameters required in this new model can be easily extracted from measured I/V curves.

The features of hole resonant tunneling in Si/sub 0.8/Ge/sub 0.2/ double barrier structures are studied both experimentally and theoretically. The theoretical calculations are based on the principles proposed in a recent study on the origin of resonant tunneling and its temperature dependence. The calculation results explain the different trends of variations with the temperature for the characteristic currents and voltages, if the first resonance is attributed to hh tunneling via the first hh subband and the second resonance to lh tunneling via first lh subband. The calculated peak current density for different structure also agrees well with the experiments in the low temperature region. The calculations show that at current resonance, the tunneling level can be higher or lower than the quasi Fermi-level in the spacer. The distinctly different temperature dependence of the first and second resonances can be understood by considering the different population of the hh and lh bands in the spacer region and the temperature dependences of E/sub f/ and effective masses. >

The authors have demonstrated a novel resonant interband tunneling device with GaSb/AlSb/InAs/GaSb/AlSb/InAs structures. It is found that InAs well thicknesses have a significant influence on the I-V characteristics of this device. The incorporation of an InAs layer in the well region will promote a peak-to-valley ratio of 20 at 300 K, nearly five times larger than that of the primitive one. Furthermore, multiple negative differential resistance behavior was obtained with InAs well thicknesses were in the range of 120 A to 300 A. Otherwise, single negative resistance is obtained. The significant influence of the added InAs layer on the electrical performance of the corresponding structure is found to be due to the electron-light hole coupling effect. >

The measured I-V characteristics of the double barrier resonant tunneling (DBRT) diode is distorted in the negative differential conductance region if the device is unstable. This paper presents a study of the I-V curve of the DBRT diode in oscillating conditions. This task is fulfilled using an accurate large signal model and PSPICE simulations. First, the PSPICE DBRT diode model is presented. Then the circuit model used for nonlinear simulations is described. Based on the simulation results, concluding remarks with regards to DBRT diode behavior are derived.

Summary form only given. We employ a numerical analysis to study the effects of a transverse magnetic field on the resonant tunneling in a double-barrier structure. An equivalent potential is introduced to represent the action of the transverse magnetic field, and the current-voltage characteristics are calculated.

In this paper we report studies on the origin of low-frequency excess noise in GaAs/Al/sub 0.4/Ga/sub 0.6/As double barrier resonant tunneleing diodes (RTDs). The RTDs were grown by molecular-beam epitaxy (MBE) on n/sup +/ (100) GaAs substrates. The double-barrier structure consists of 32-/spl Aring/-thick Al/sub 0.4/Ga/sub 0.6/As barriers and a 48-/spl Aring/-thick GaAs quantum well. The band discontinuity is about 0.325 eV. The background impurity concentration in the double-barrier structure is approximately 10/sup 15/ cm/sup -3/.

We have demonstrated room temperature negative differential resistance with a high peak-to-valley ratio of nearly 10/sup 6/ using CdF/sub 2//CaF/sub 2/ double barrier resonant tunneling diode (DBRTD) structures grown on a Si(111) substrate. Fluctuation of layer thickness is evaluated at /spl plusmn/lTL (tri-layer=0.31 nm) for each layer. The I-V curves are reasonably dependent on the layer thickness of the CdF/sub 2/ quantum-well.

We propose a novel CrTiN/TiN double barrier layer technology for high-density COB structure applications. After furnace annealing at 800/spl deg/C for 30min, a 0.35/spl mu/m poly-Si contact test structure with the Pt/CrTiN/TiN layer was found to maintain ohmic behaviors and provide a resistance of about 1k/spl Omega/. In addition, these contact structures successfully exhibited long time thermal stability at 750/spl deg/C. The findings of this study suggest that the CrTiN/TiN double barrier layer method is suitable for the COB structure in order to realize high-density ferroelectric memory applications.

We have studied the role of GaP intermediate layers in GaInP/GaAs double barrier resonant tunnelling structures. Measurements of the current-voltage characteristics show an asymmetric behaviour which was improved in diodes including thicker GaP intermediate layers. From cross-sectional transmission electron microscopy investigations we have observed a fluctuation in the thickness of the GaP layers at the GaInP to GaAs transition to which we attribute the asymmetric characteristics. Finally, we demonstrate a simplified structure using only GaP layers as barriers. These new diodes show more symmetric I-V characteristics than the GaInP/GaAs tunnelling diodes.

A quantum well double barrier diode has been tested as a frequency tripler from 63.7 GHz to 191 GHz in a crossed waveguide mount designed for use with GaAs varactor diodes. Output power of 250 μw has been generated with an efficiency of 0.61 %. This performance is comparable to that obtained from a GaAs varactor diode with the same cutoff frequency.