Simulation of a resonant tunneling diode using an entropic quantum drift-diffusion model

We present an entropic Quantum Drift Diffusion model (eQDD). Some links between this model and other existing models are exhibited, especially with the Classical Drift-Diffusion (CDD) model, the Density Gradient (DG) model and the Schrödinger-Poisson model (SP). Numerical results show that the model captures important features concerning the modeling of a resonant tunneling diode. To finish, some comparisons between the models stated above are realized.     

The design and fabrication on gate type resonant tunneling transistor

In light of fabricating resonant tunneling diode (RTD), in this paper a GaAs-based resonant tunneling transistor with gate structure (GRTT) has been designed and fabricated successfully. A systematic depiction centers on the designs of material structure, device structure, photolithography mask, fabrication of device and the measurement and analysis of parameters. The fabricated GRTT has a maximum PVCR of 46 and a maximum transconductance of 8 mS. The work lays the foundation for further improvement on the performance and parameters of RTT. __________ Translated from Chinese Journal of Semiconductors, 2006, 27(11): 1974–1980 [译自: 半导体学报]     

Scaling dependence of electron transport in nano-scale Schottky barrier MOSFETs

The scaling dependence of electron transport in the double-gated Schottky barrier MOSFET (DG-SBT) below 10 nm is investigated in the framework of quantum transport theory, using non-equilibrium Green’s function method. Simulation results show that the current-voltage characteristics in ultra-small DG-SBT are characterized by both resonant and direct tunneling effects. The electron potential in the 10-nm-scale DG-SBT surrounded by Schottky barriers acts as a resonant cavity and produce a negative differential resistance due to resonant tunneling effect. While, further scaling shallows the depth of the cavity and makes it difficult to form resonance levels. Hence, at the scaling limit, direct tunneling currents simply dominate the current-voltage characteristics of DG-SBT.     

Modeling of peak voltage and current of nanowire resonant tunneling devices: case study on InAs/InP double‐barrier heterostructures

In this paper, we develop an analytical model for the prediction of the peak voltage and the current in the current–voltage characteristics of nanowire resonant tunneling heterostructures. The model is applied in the case study of double‐barrier InAs/InP devices, and the results are obtained from numerical carrier transport calculations, in terms of structural parameters such as the nanowire radius as well as the width of the barriers and quantum well. Copyright © 2013 John Wiley & Sons, Ltd.     

Self-consistent quantum transport theory: Applications and assessment of approximate models

We have implemented a fully self-consistent non-equilibrium Green’s function approach for vertical quantum transport in open quantum devices with contacts and study theoretically quantum well heterostructures, resonant tunneling diodes and quantum cascade laser structures in this formalism. We systematically investigate the role and consequences of several widely used approximations such as decoupling the equations for the scattering states and their occupation, neglect of inelastic scattering, and neglect of nonlocal scattering self-energies.     

Bias-induced destruction of ferromagnetism and disorder effects in GaMnAs heterostructures

The magneto-electric properties of resonant tunneling double barrier structures using GaMnAs for the quantum well is investigated within a self-consistent Green??s function approach and a tight-binding electronic structure model. The magnetic state of the well is determined self-consistently by the tunneling current which controls the hole spin density and, hence, the degree of exchange splitting of the subbands inside the well. Prompted by recent experiments we compare model systems of increasing defect concentration (substitutional disorder) regarding their I?CV curve, magnetic state, and spin polarization. We predict that, near resonance, the ferromagnetic order which may be present at zero bias in the GaMnAs well tends to be destroyed. Resonance peaks are found to be more sensitive to disorder than ferromagnetic ordering and spin polarization of the steady-state current.     

Does Circulation in Individual Current States Survive in the Total Current Density?

We describe the two-dimensional simulation of a bent resonant tunneling diode structure which displays vortices in its total current density pattern over a range of applied bias. In contrast, a double gate n-MOSFET is shown where such circulation exists in individual subband states but does not survive in the total current density solution. Both devices are simulated assuming ballistic quantum transport in Si at 300 K.     

Shot noise in resonant tunneling diodes using the non-equilibrium Green’s functions calculation

The non-equilibrium Green function (NEGF) technique is used to solve the quantum transport equation in resonant tunneling diodes (RTDs). The charge interaction is treated self-consistently to include rigorously the space-charges effects. Reasonable results for the potential profile, the transmission probability, and the current-voltage characteristics have been obtained. The effect of temperature on the current-voltage (I-V) characteristics is investigated. Particularly, the current noise spectral density has been extracted following both coherent and sequential tunneling approaches. Our conclusion of the dominance of the coherent and sequential tunneling according to the transport regime is consistent with recent theoretical analyses and experimental data.     

RTD Relaxation Oscillations, the Time Dependent Wigner Equation and Phase Noise

Wigner simulations of resonant tunneling diode (RTD) self-excited oscillations are discussed with respect to the upper frequency limit of operation and their sensitivity to large scale perturbations. These studies offer the most practical assessment of phase noise, response times of RTDs and of the coupling of quantum well space charge to its environment.     

NEGF simulation of the RTD bistability

The simulation of I-V characteristics of Al_0.3Ga_0.7As-GaAs and AlAs-GaAs resonant tunneling diodes (RTD) is presented. The nonequilibrium Green function (NEGF) based 1D quantum transport simulator Wingreen is used in our case. The plateau region on the IV characteristics usually present only by the Wigner function equation (WFE) based simulation appeared now by the NEGF simulation of our AlAs-GaAs RTD and its shape is comparable with our experimental measurements. Analysis of our results from point of view of the scattering and geometrical parameters of the RTD structure is presented.     

Semiconductor quantum devices

The operation of devices with small enough dimensions for electrons to exhibit wavelike behavior is explained. Two types of device are examined: vertical quantum devices, which include the resonant tunneling structure and the single-electron transistor, and lateral, which include the quantum interference transistor and the spin precession device. The advantages and drawbacks of the two types are identified     

A novel 3-D integrated HFET/RTD frequency multiplier

A merged heterostructure field-effect transistor/resonant tunneling diode (HFET/RTD) combination is proposed to act as a (sub)millimeter wave source via highly efficient frequency multiplication and its functionality is demonstrated at intermediate frequency. On a semi-insulating InP-substrate a HFET followed by a double barrier RTD-layer sequence is grown in a single molecular beam epitaxy (MBE)-run. A novel monolithic frequency multiplier circuitry is developed where the RTD is used as load in contrast to other concepts where the RTD is inserted in the input of a three-terminal device. The resulting output voltage is rectangular type and rich in higher odd harmonics. This approach avoids classical disadvantages of the RTD because biasing in the negative-differential-regime is not required and bistability of the I-V-characteristic is used rather than the negative differential resistance. The small signal parameters of the single devices realized with optical lithography, wet etching, and self-aligned process technology are used as input data for a microwave design software (MDS) and the frequency multiplication is modeled up to submillimeter wave frequencies     

Smooth Quantum Hydrodynamic Model vs. NEMO Simulation of Resonant Tunneling Diodes

The smooth quantum hydrodynamic model is an extension of the classical hydrodynamic model for semiconductor devices which can handle in a mathematically rigorous way the discontinuities in the classical potential energy which occur at heterojunction barriers in quantum semiconductor devices. Smooth QHD model simulations of the current-voltage curves of resonant tunneling diodes are presented which exhibit negative differential resistance—the experimental signal for quantum resonance effects—and are compared with the experimentally verified current-voltage curves predicted by the simulator NEMO, which uses a non-equilibrium Green function method.The NEMO work described in this article was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration. This material is also based upon work supported by the National Science Foundation under Grant No. EEC-0228390.     

Accuracy balancing for the finite-difference-based solution of the discrete Wigner transport equation

The Wigner transport equation based on the Wigner function which is defined on the phase space describes two actions in orthogonal directions of the phase space: movement (diffusion) in position space and transition in momentum space. Here, we show that for the proper analysis of a resonant tunneling diode using the finite-difference-based solution of the Wigner transport equation, the degree of numerical accuracy in the calculation of the movement in position space should be balanced with that in the evaluation of the transition in momentum space.     

Numerical Simulation for Direct Tunneling Current in Poly-Si-Gate MOS Capacitors

We have numerically simulated gate tunneling current in MOS capacitors. Price has demonstrated that the Gamow formulation can be applied to analysis of the escape of electrons from channel into gate in MOSFETs [P.J. Price, Appl. Phys. Lett., 82, 2080 (2003)]. We have integrated the Gamow method into a Schrödinger-Poisson solver for metal-gate and poly-Si-gate n-type MOS capacitors. The numerical results of the tunneling current are then compared with experimental results.     

盾构同步注浆和加泥/加水监控系统开发

隧道盾构施工会对地下底层产生扰动,对地面建筑物产生影响。为了避免在施工过程中引发地面塌陷、隆起等事故,提出了对隧道盾构挖掘进程中的同步注浆和加泥/加水施工方案。引入了监控自动控制系统,采用建立数学模型的方法进行地表沉降实时监视与控制,以确保盾构施工的安全进行。该系统对盾构同步注浆和加泥/加水过程进行监控,能够准确的检测、评估和发现盾构掘进过程中可能引起地表沉降的各种工况,并且进行了补偿控制,提出了改进方案,优化了设计参数。     

铁磁/重金属双层膜结构中电流驱动的铁磁共振

在理论上研究了具有垂直磁各向异性铁磁/重金属双层膜结构中电流驱动的铁磁共振。通过线性展开包含自旋霍尔效应自旋矩项的Landau-Lifshitz-Gilbert方程,获得了交流电流频率和直流电流密度调节的铁磁共振谱。发现平衡位置、共振位置和共振线宽都可以通过改变直流电流密度和外磁场的大小进行调节。联合自旋霍尔效应感应的交流和直流自旋矩,可以减小电流感应磁矩反转的临界电流密度。     

基于隧道效应的纳米级振动检测及测量

扫描隧道显微镜是高精度纳米级表面测量仪器,由于扫描隧道显微镜工作时的隧道间隙在几个纳米左右,外界任何微小的随机振动传递到仪器都会对测量结果产生影响,失去被测物表面的特征信息.因此,研究微振动,特别是低频纳米级振动在隧道状态下对隧道间隙的影响具有很重要的意义.实验表明,实验系统在隧道状态下对纳米级振动有很好的幅频响应.     

A multi-purpose Schrödinger-Poisson Solver for TCAD applications

We present the Vienna Schrödinger-Poisson Solver (VSP), a multi-purpose quantum mechanical solver for investigations on nano-scaled device structures. VSP includes a quantum mechanical solver for closed as well as open boundary problems on fairly arbitrary one-dimensional cross sections within the effective mass framework. For investigations on novel gate dielectrics VSP holds models for bulk and interface trap charges, and direct and trap assisted tunneling. Hetero-structured semiconductor devices, like resonant tunneling diodes (RTD), can be treated within the closed boundary model for quick estimation of resonant energy levels. The open boundary model allows evaluation of current voltage characteristics.