Monte Carlo study of two-dimensional electron gas transport in Si-MOS devices

By using Monte Carlo simulations the effective mobility and high field drift velocity of a quasi-two-dimensional electron gas in Si-MOS devices have been calculated. For this calculation the three lowest subbands and an ensemble of scattering quantities (fixed oxide charge, surface roughness, and several modes of phonons) have been taken into account. The relative population of the E₀- and E₀′-subbands is calculated for channel charge densities between 10¹² and 10¹³ cm^?2. The dependence of the carrier drift velocity on the field in the inversion layer is studied for several values of fixed oxide charge and surface roughness in a wide field range. Finally the effective mobility is considered as a function of temperature, channel charge density, surface field, fixed oxide charge, and surface roughness. The computed results are compared with the most recent experimental data. A good agreement is found.     

A Monte Carlo study of absolute phase determination

The problem of absolute phase tracking and the development of the properties of an optimal estimator of absolute phase are considered. Using Monte Carlo simulation, this estimator's performance is compared with that of the phase-locked loop on the basis of slip distribution growth rate. Further slip prediction is considered and a statistic, based on the entropy of the conditional distribution of the phase given the observations, is shown to be effective.     

Monte Carlo calculation of noise transport in a two-dimensional diode

The noise transport phenomena in a two-dimensional diode operated under space-charge-limited conditions are investigated by means of the statistical Monte Carlo method. Effects on the transport characteristics of an electron beam by the multi-dimensional nature of the potential distribution in the vicinity of the potential minimum are evaluated. Contrary to both the single velocity and multivelocity linear small-signal noise theories, the noise parametersS, II,S-- II andS+ II are found to be nonconservative. A reduction in the equivalent noise figure from 6.96 db corresponding to full-shot noise input at the cathode to approximately 2 db is observed at the anode of the two-dimensional diode for a wide range of frequencies. A substantial amount of correlation between the kinetic potential and the current fluctuations is developed in the multivelocity region beyond the potential minimum. It is believed that the improvement in noise performance of the two-dimensional diode over the one-dimensional model is directly attributable to the space-charge potential-depression effects by which an additional amount of velocity spread is introduced in the electron beam, creating an extension of the multivelocity non-linear region. The theoretical minimum-noise figures obtained indicate that possibly two-dimensional dc effects are more important than two-dimensional ac effects in essentially hollow-beam low-noise devices.     

A Monte Carlo particle study of the intrinsic noise figure in GaAs MESFET's

The Monte Carlo particle model is well suited for noise studies as it reflects the basic transport physics and exhibits the same momentum and spatial distributions and fluctuations as the real semiconductor component. The model has been used to study the noise properties of a GaAs MESFET. The noise figure extracted is intrinsic, as the only contributions to it originate from the transistor itself, and does, therefore, exclude any effects of contact metallization and interface effects. This means that our definition of the noise figure has to deviate from the conventional one. It is found that fluctuations in the source current reduce the intrinsic noise figure significantly in a recessed gate structure, while the drain current fluctuations do not contribute to it.     

Effects of carrier heating on laser dynamics-a Monte Carlo study

The static and dynamic properties of semiconductor quantum-well (QW) lasers have traditionally been analyzed by using rate equations that couple cold carriers to photons in the lasing cavity. This assumption of cold carriers, however, has often been disputed because it does not account for heating due to carrier relaxation, hot phonon effects, and spectral hole burning. All these processes affect laser performance significantly by modifying the gain because gain depends on carrier temperature as well as spectral broadening. In this paper, we study the carrier dynamics of QW lasers using a Monte Carlo method and conclude that hot carrier effects in semiconductor lasers are important and need to be considered for the analysis and design of semiconductor lasers     

Monte Carlo study of Germanium n- and pMOSFETs

In this paper, we perform fullband Monte Carlo simulations of Ge bulk nand pMOSFETs and compare them with their Si counterparts. We consider transport in the presence of phonon, ionized impurity, surface roughness scattering, and impact ionization. Quantum confinement in the inversion layer is taken into account in the form of a modified potential. Germanium devices gave higher drive current when compared with Si devices for the device structures studied. Consistent with the arguments of Lundstrom, the performance enhancement of Ge MOSFETs lies between that which would be expected based on the higher mobility alone, and the much smaller advantage, if any, offered in the ballistic limit where transport is governed by thermal injection velocities from the source.     

Monte Carlo study of strained GermaniumNanoscale bulk pMOSFETs

In this paper, we perform fullband Monte Carlo simulations of nanoscale strained Ge bulk pMOSFETs with compressive strain in the strained Ge layer. We consider transport in the presence of phonon, ionized impurity, surface roughness scattering and impact ionization. Quantum confinement in the inversion layer is taken into account in the form of a modified potential. Strained Gedevices gave higher drive current when compared with unstrained Ge devices for the device structures studied.     

Transient space-charge-perturbed currents in organic materials: A Monte Carlo study

The transient current holds rich information about carrier transport and is used to derive charge mobility in the time-of-flight (TOF) measurement. Because carriers have finite charge, all transient currents are space-charge-perturbed (SCP). Previous theories of transient SCP currents are derived by neglecting diffusion and assuming a constant mobility, which is unfit for organic materials because of the hopping behavior of carriers. Due to the lack of knowledge, we do not fully understand the results from TOF experiments, which hinders the understanding of the charge transport mechanisms. Here, we perform Monte Carlo simulations of multi-particle carrier movement to study the transient SCP currents in organic materials. Coulomb interactions are calculated, and it is assumed that multiple carriers cannot occupy the same site simultaneously. Our results show that space-charge perturbation has two opposite effects on charge transport. In most cases, the net result is slower carrier movement, which suggests that TOF measurements under SCP conditions underestimate the charge mobility of organic materials.     

Properties of wurtzite GaN MESFETs studied by two-dimensional full band Monte Carlo approach

The properties of a GaN Metal-Semiconductor Field Effect Transistor were studied based on two-dimensional full band Monte Carlo simulations. The dependences of the distributions of the electric potential, electron concentration, electric field, drift velocity, and average electron energy on the gate-source voltage (V_GS) and drain-source voltage (V_DS) were obtained, then the characteristics of the drain current (I_DS) versus the drain-source voltage (V_DS) and the transconductance (G_m) versus V_GS characteristics were determined. At and I_DS is 5.03 A/cm, which is higher value. The G_m−V_GS curve shows bell shaped and the maximum G_m is 112 ms/mm at and The current gain cutoff frequency (f_T) is 98 GHz at and      

Monte Carlo study of the dynamic breakdown effects in HEMT's

We present a theoretical investigation of the near-breakdown scenario in pseudomorphic high electron mobility transistors (HEMT's). We show that the main mechanism for the enhanced drain current is a parasitic bipolar effect due to holes, generated by impact ionization, which accumulate in the channel and in the substrate close to the source contact. The dynamic of this charge accumulation and of the consequent drain current increase is studied by means of a two-dimensional (2-D) Poisson Monte Carlo simulator     

Monte Carlo simulation of the low-temperature mobility of two-dimensional electrons in a silicon inversion layer

The transport of two-dimensional electrons in a silicon inversion layer is determined by Monte Carlo simulation in the temperature range 4.2–40 K, where the electrical quantum limit occurs and only the lowest subband is populated. Two scattering mechanisms are taken into account: scattering by distant ionized impurities and scattering by surface roughness elements, along with their dependence on the polarizability of the two-dimensional electron gas. The mobility and coefficient of warm electrons in weak electric fields are calculated. The data are compared with previously published results. Fiz. Tekh. Poluprovodn. 31, 89–92 (January 1997)     

Monte Carlo simulation of a two-dimensional random rough surface using the sparse-matrix flat-surface iterative approach

The exact solution of scattering by a two-dimensional random rough surface (three-dimensional scattering problem) with moderate RMS height and slopes is calculated using a new numerical method called the sparse-matrix flat-surface iterative approach. Comparison is also made with the second-order Kirchhoff approximation.<>     

A Monte Carlo method for radar backscatter from a half-space randommedium

The problem of electromagnetic multiple scattering in a random medium is treated by a Monte Carlo method, in which an incident beam of photons is progressively scattered by scattering centers in the medium. The theory characterizes each scattering by functions describing the probability of the photon being scattered or absorbed, and the probability of its being scattered into certain directions. This process is tracked until the photon is finally absorbed or backscattered into the receiver. Variance reduction techniques are introduced to reduce the computation time required for acceptable ensemble averages of the backscattering cross sections. Ellipsoidal dielectric scatterers are used to model circular disk-shaped leaves, elliptical disk-shaped leaves, and needle-shaped leaves, which are randomly distributed in a half-space medium. The Monte Carlo simulations give good comparison with experimental data of backscattering cross sections from fields of wheat, corn, and milo     

Monte Carlo study of electron relaxation in quantum-wire laserstructures

Very-low threshold currents are expected to be achieved in quantum-wire lasers owing to the singularity in the density of states occurring at the bandedge. On the other hand, the high-speed modulation of quantum-wire lasers may be limited by carrier relaxation processes that are greatly affected by the reduction in the momentum space. In this paper, we calculate the electron relaxation times for GaAs/AlGaAs wires of various cross sections assuming that electrons are injected in a thermal distribution at the edge of the potential well formed by the barrier. The relaxation times are extracted from the time evolution of the carrier distribution as the electrons come to thermal equilibrium with the lattice. The Monte Carlo method is used to simulate the details of the relaxation process with the inclusion of electron-bulklike phonon, electron-electron and electron-hole interactions. We find that the electron relaxation times range from 120 ps for the 100×100 Å wire to 30 ps for the 200×200 Å wire for a carrier density of 10¹⁸ cm^-3. When the electron-hole interaction is included into the calculations, the equilibration time for the 100×100 Å wire is reduced to ≈50 ps. Screening effects are incorporated using the Thomas-Fermi formalism. At a carrier concentration of 10¹⁶ cm^-1, the equilibration times for the corresponding wire sizes are 20 and 5 ps. Thus, the relaxation time calculated within the limits of our model decreases with an increased wire cross section. This trend indicates the presence of a trade-off between speed and efficiency in quantum-wire lasers considering that the threshold current is decreased by reducing the wire cross section     

A Monte Carlo approach for power estimation

The authors investigate a power estimation technique for VLSI that combines the accuracy of simulation-based techniques with the speed of the probabilistic techniques. The resulting method is statistical in nature; it consists of applying randomly generated input patterns to the circuit and monitoring, with a simulator, the resulting power value. This is continued until a value of power is obtained with a desired accuracy, at a specified confidence level. The authors present the algorithm and experimental results, and discuss the superiority of the approach     

Dynamical study of the transferred-electron effect by a Monte Carlo technique

The dynamic behaviour of transferred-electron devices is investigated by a Monte Carlo method. As an example, the frequency dependence of the efficiency, is presented for InP. The frequency behaviour of the efficiency is shown to be very sensitive to the ?L coupling constant     

A percolation study of RTS noise amplitudes in nano-MOSFETs by Monte Carlo simulation

A high efficiency 2D percolation model of RTS amplitudes in nanoscale MOSFETs based on the numerical results of potential and carriers density distributions in the channel obtained by solutions of coupled 2D Schrodinger and Poisson equations was presented. Using this model the dependences of relative RTS amplitudes ΔI_D/I_D on device geometry L_eff × W_eff, t_ox bias conditions I_D, V_G and trap locations along the channel were simulated and analyzed for a set of square n-MOSFETs. The results show reasonable agreement with published numerical or experimental data.     

A Wigner function-based quantum ensemble Monte Carlo study of a resonant tunneling diode

We present results of resonant tunneling diode operation achieved from a particle-based quantum ensemble Monte Carlo (EMC) simulation that is based on the Wigner distribution function (WDF). Methods of including the Wigner potential into the EMC, to incorporate natural quantum phenomena, via a particle property we call the affinity are discussed. Dissipation is included via normal Monte Carlo procedures and the solution is coupled to a Poisson solver to achieve fully selfconsistent results.     

蒙特卡罗法模拟电子表面弹性碰撞

用蒙特卡罗法模拟电子在固体表面的弹性碰撞过程,得到电子的弹性反射系数η_E及弹性背散射电子的角分布。给出η_E与电子非弹性平均自由程(IMFP)λ的函数关系,用η_E的实验值推算出λ。与文献报道的λ实验值及Seah,Penn等经验公式计算的λ值相比,发现本文计算的λ与实验值符合较好。