Simulation Of Resonant Tunneling Diodes Research Articles

Wigner Transport Simulation of Resonant Tunneling Diodes with Auxiliary Quantum Wells

Resonant-tunneling diodes (RTDs) with auxiliary quantum wells (e.g., emitter prewell, subwell, and collector postwell) are studied using a Wigner transport equation (WTE) discretized by a thirdorder upwind differential scheme. A flat-band potential profile is used for the WTE simulation. Our calculations revealed functions of the auxiliary wells as follows: The prewell increases the current density (J) and the peak voltage (Vp) while decreasing the peak-to-valley current ratio (PVCR), and the postwell decreases J while increasing the PVCR. The subwell affects J and PVCR, but its main effect is to decrease Vp. When multiple auxiliary wells are used, each auxiliary well contributes independently to the transport without producing side effects.

Effective Potential from the Generalized Time-Dependent Schrödinger Equation

We analyze the generalized time-dependent Schrödinger equation for the force free case, as a generalization, for example, of the standard time-dependent Schrödinger equation, time fractional Schrödinger equation, distributed order time fractional Schrödinger equation, and tempered in time Schrödinger equation. We relate it to the corresponding standard Schrödinger equation with effective potential. The general form of the effective potential that leads to a standard time-dependent Schrodinger equation with the same solution as the generalized one is derived explicitly. Further, effective potentials for several special cases, such as Dirac delta, power-law, Mittag-Leffler and truncated power-law memory kernels, are expressed in terms of the Mittag-Leffler functions. Such complex potentials have been used in the transport simulations in quantum dots, and in simulation of resonant tunneling diode.

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.

Current spreading in contact layers and model for 2D numerical calculation of resonant-tunneling diode

Quasi-two-dimensional (2D) simulation of resonant-tunneling diode is presented. 2D effects are studied both analytically and numerically. For numerical simulation, the local resonant-tunneling layer (RTL) model is implemented in 2D drift–diffusion simulator as the boundary condition for the current. It is shown that the increase of linear size of the device results in the strong decrease of peak current and increase of valley current. For the device with large current density, designed for high-frequency applications, the 2D effects appear already at linear size about 1 μm. The local model for current through RTL can be used for 2D or 3D numerical simulation of a wide variety of devices including the RTL, such as heterojunction bipolar transistor, resonant-tunneling transistor etc.

Wigner function quantum Monte Carlo

Results obtained from a Wigner function quantum Monte Carlo simulation of resonant tunneling diodes are presented. Methods of introducing partial weights of electrons through an affinity as well as methods for incorporating negative values of the Wigner function are discussed. Results showing tunneling and correlation build-up during resonance are presented as evidence of a working model.

Multi-band simulation of resonant tunneling diodes with scattering effects

The effects of polar optical phonon (POP) scattering and interface-roughness (IR) scattering on the current of GaAs/AlAs resonant tunneling diodes (RTDs) are simulated based on a multi-band, non-equilibrium Green's function method. Space charge effect is also taken into account by solving the Poisson's equation self-consistently. As a result, we have found that the multiband nature and space charge effects significantly change the results of conventional RTD simulations and the POP scattering has a more significant effect on the valley current than IR scattering.

Simulation of resonant tunneling diodes with a generalized quantum transport theory

Modeling of quantum transport based on the non-equilibrium Green functions is presented in resonant tunneling diodes (RTD's) where realistic band structures, space charge effect, and scattering effects are taken into account. We have developed a multiband, non-equilibrium Green function and Poisson simulator that employs multi-band (MB) tight binding calculation using a sp 3s ∗ hybridization. As a result, we have found that the multiband nature and polar optical phonon scattering effects significantly change the results of conventional RTD simulations.

Quantum Simulation of Resonant Tunneling Diodes: a Reliable Approach Based on the Wigner Function Method

In this work, we demonstrate that the limitations of previous simulation tools for resonant tunneling diodes based on the Wigner function approach, can be overcome by coupling a classical Monte Carlo solver to the quantum Liouville equation, the former being applied to regions far enough from the double barrier, where quantum effects are not present. This allows us to extend the simulation domains up to hundreds of nanometers, without paying a penalty in computational burden. It is shown that this large domains are necessary to obtain an accurate description of device behavior. By using physical parameters corresponding to those of actual devices, we have found current oscillations and a plateaulike behavior in the negative conductance region in accordance to experimental I-V characteristics obtained on resonant tunneling diodes.

Quantum Monte Carlo simulation of resonant tunneling diodes based on the Wigner distribution function formalism

A tool for the simulation of resonant tunneling diodes (RTDs) has been developed. This is based on the solution of the quantum Liouville equation in the active region of the device and the Boltzman transport equation in the regions adjacent to the contacts by means of a Monte Carlo algorithm. By accurately coupling both approaches to current transport, we have developed a quantum simulation tool that allows the use of simulation domains much larger and realistic than those previously considered, without a significant increase in computational burden. The main characteristics expected for the considered devices are clearly obtained, thus supporting the validity of our tool for the simulation of RTDs.

A note on current-voltage characteristics from the quantum hydrodynamic equations for semiconductors

The quantum hydrodynamic model is primary used for the simulation of resonant tunneling diodes. The current-voltage characteristics of these diodes show negative differential resistance (NDR) effects. For two simplified one-dimensional quantum models derived by means of asymptotic analysis, explicit formulas of the current-voltage characteristics are given. It turns out that not only the quantum correction term but also the convection term are mathematically responsible for the NDR effects. This observation is confirmed by numerical simulations of the full isothermal quantum hydrodynamic model.

High frequency simulation of resonant tunneling diodes

The small and large-signal response of the resonant tunneling diode at high-frequencies is studied using a quantum simulator. The Poisson and Schrodinger equations are solved self-consistently for each harmonic using the harmonic balance technique. This ensures that the total current, consisting of the displacement plus conduction currents, is conserved across the device for each harmonic. The RTD exhibits an increased capacitance in the negative differential conductance (NDC) region in agreement with experimental data. As recently proposed this capacitance increase results from the formation of an emitter well capacitor when the well discharges. The derivation of the RTD capacitance from a quasi-static analysis using the differential variation of the de charge in the RTD is shown to be not applicable because the RTD well charges through the cathode but discharges through the anode. The frequency dependence of the conductance and susceptance is similar to reported experimental data. A large frequency dependence of the admittance is only observed when the RTD is biased in the negative differential conductance (NDC) region. These calculations predict an effective reduction of the RTD conductance and capacitance at high-frequency in the NDC region. This effect can be modeled using a quantum inductance in series with the negative resistance of the RTD as recently proposed. Due to the simultaneous reduction of both the conductance and the capacitance at high-frequency in the NDC region the maximum frequency of oscillation does not differ much from its estimate using the low frequency conductance and capacitance. The large-signal response at high-frequency of an RTD biased in the negative differential region is also presented in this paper. The large-signal negative-conductance is shown to decrease with both increasing frequency and ac voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effects of scattering on current-voltage characteristics, transient response, and particle trajectories in the numerical simulation of resonant tunneling diodes

The relaxation-time approximation is used in the numerical simulation of the Wigner distribution function to incorporate scattering. The effects within the constant relaxation-time approximation are (a) a decrease in the peak-to-valley ratio of the current-voltage curve; (b) a reduction in the oscillations of the Wigner distribution function, especially at resonance bias; (c) a suppression of the decay time of current oscillations after a sudden bias shift, indicating a smaller switching time than for no scattering; (d) a degradation in the resonant tunneling trajectories towards the characteristics of nonresonant trajectories; (e) a decrease in the spatial range of the quantum influences near resonance; and (f) ballistic transport sets in [i.e., the mean free path of the electrons is greater than the barrier region (110 Å)] for temperatures less than 74 K.