光泵调制掺杂阶梯量子阱THz激光器瞬态动力学的Monte Carlo模拟

采用系综Monte Carlo（EMC）方法首次对光泵量子阱THz激光器的载流子瞬态动力学进行了分析。提出的器件原型为三能级调制掺杂GaAs/GaxAl(1-x)As系列非对称阶梯量子阱,激射频率为6.1THz。模拟中包括了电子-电子、电子-光学声子和电子-声学声子等散射机制,采用调制掺杂以得到较高电子密度可以忽略电子-电离杂质散射。已报道的研究工作都是在量子阱中掺杂,而对于这种器件原型能否得到电子布居反转,报道的结果也是相互矛盾。器件原型在温度为77K,光泵强度达到一定值时可以得到电子布居反转,所得到的研究结果对相关的实验研究具有一定的指导意义。     

Impact of resonance-state scattering on the kinetics of two-dimensional electrons

Kinetics of electrons occupying two subbands in a quantum well in the presence of a high in-plane accelerating electric field is studied taking into account optical-and acoustic-phonon scattering and scattering via resonance quasi-stationary states associated with shallow donors. Resonance scattering is analyzed in the context of the well-known Breit–Wigner model. The distribution function is constructed using the “random-walk” Monte Carlo method. Resonance-state scattering leads to the accumulation of electrons in the vicinity of the resonance state and, in general, to a considerable modification of the streaming-regime distribution function. The dependence of relative occupancies of the two subbands on the lattice temperature is determined.     

MC simulation of strained-Si MOSFET with full-band structure and quantum correction

A new two-dimensional full-band Monte Carlo simulator, "Monte Carlo University of Texas" (MCUT) is introduced and described in this paper. MCUT combines some of the best features of semiclassical MC device simulation including full-band structure and flexibility of scattering processes, with generality of material composition and the ability to address degeneracy breaking among energy valleys and the associated effects on scattering and transport due to quantum confinement and strain effects. The latter capability derives from extension of a prior crystal-momentum-independent self-consistent Poisson-Schro/spl uml/dinger-based quantum corrected potential, to a valley dependent quantum correction via, in part, a new modeling concept of "effective strain" within the full-band structure code. Low field mobility simulation results for large tensile strained-Si channel nMOSFETs and unstrained-Si channel nMOSFETs device are compared with other simulation methods and experimental data to demonstrate the effectiveness of the approach, and the abilities to simulate high-field transport and transport in devices of a few 10s of nanometer channel lengths are briefly demonstrated.     

Modeling hot-electron gate current in Si MOSFET's using a coupleddrift-diffusion and Monte Carlo method

A coupled two-dimensional drift-diffusion and Monte Carlo analysis is developed to study the hot-electron-caused gate leakage current in Si n-MOSFETs. The electron energy distribution in a device is evaluated directly from a Monte Carlo model at low and intermediate electron energies. In the region of high electron energy, where the distribution function cannot be resolved by the Monte Carlo method due to limited computational resources, an extrapolation technique is adopted with an assumption of a Boltzmann tail distribution. An averaging method is employed to extract the effective electron temperature. Channel hot electron injection into a gate via quantum tunneling and thermionic emission is simulated, and electron scattering in the gate oxide is taken into account. The calculated values of gate current are in good agreement with experimental results. The simulation shows that the most serious hot electron injection occurs about 200-300 Å behind the peak of average electron energy due to a delayed heating effect     

An analytical, aperture, and two-layer carrier diffusion MTF andquantum efficiency model for solid-state image sensors

A two-dimensional analytical model is formulated for calculating the pixel response, modulation transfer function (MTF), and quantum efficiency of front-side illuminated, solid-state image sensors. Included in this unified model are the effects of lateral diffusion of charge carriers within a two-layer substrate and less than full pixel sampling apertures. The results of this model are compared to those of a numerical, three-dimensional Monte Carlo algorithm and to the analytical results reported by Blouke and Robinson. We find good agreement between the quantum efficiency and MTF calculated by the present model and by the three-dimensional Monte Carlo method. However, we find higher quantum efficiency and lower MTF than the previously reported analytical two-layer model. The unified aspect of the present model correctly combines the effects of sampling aperture and lateral diffusion     

A quantum correction based on Schrodinger equation applied to Monte Carlo device simulation

A full-band Monte Carlo model has been coupled to a Schrodinger equation solver to account for the size quantization effects that occur at heterojunctions, such as the oxide interface in MOS devices. The overall model retains the features of the well-developed semi-classical approach, by treating self-consistently the Schrodinger solution as a correction to the particle-based Monte Carlo. The simulator has been benchmarked by comparing results for MOS capacitors and double gate structures with a self-consistent quantum solution, showing that the proposed approach is efficient and accurate. This quantum correction methodology is extended to device simulation, by accounting for the interplay between confinement and transport through a parameter which we call "transverse" temperature. This approach appears to be valid even for nanometer-scale devices in which nonequilibrium ballistic transport is occurring. We present simulations of a 25-nm MOSFET and compare results obtained with and without the quantum correction.     

Investigation of plasmon-induced losses in quasi-ballistic transport

We present an ensemble Monte Carlo (EMC) simulation of the effect of electron-electron (e-e) and electron-plasmon (e-pl) interactions on the transient behavior of electrons under high energy injection conditions. It is shown that, in a situation that closely resembles that obtained in the base of a planar-doped barrier (PDB) transistor, the coulombic interaction severely limits the possibility of ballistic transport.     

Integration of a particle-particle-particle-mesh algorithm with theensemble Monte Carlo method for the simulation of ultra-smallsemiconductor devices

A particle-particle-particle-mesh (P³M) algorithm is integrated with the ensemble Monte Carlo (EMC) method for the treatment of carrier-impurity (c-i) and carrier-carrier (c-c) effects in semiconductor device simulation. Ionized impurities and charge carriers are treated granularly as opposed to the normal continuum methods and c-i and c-c interactions are calculated in three dimensions. The combined P³M-EMC method follows the approach of Hockney (1981), but is modified to treat nonuniform rectilinear meshes with arbitrary boundary conditions. Bulk mobility results are obtained for a three-dimensional (3-D) resistor and are compared with previously reported experimental and numerical results     

Study of a 50 nm nMOSFET by ensemble Monte Carlo simulationincluding a new approach to surface roughness and impurity scattering inthe Si inversion layer

A 50 nm nMOSFET has been studied by Ensemble Monte Carlo (EMC) simulation including a novel physical model for the treatment of surface roughness and impurity scattering in the Si inversion layer. In this model, we use a bulk-like phonon and impurity scattering model and surface-roughness scattering in the silicon inversion layer, coupled with the effective/smoothed potential approach to account for space quantization effects. This approach does not require a self-consistent solution of the Schrodinger equation. A thorough account of how these scattering mechanisms affect the transport transient response and steady-state regime in a 50 nm gate-length nMOSFET is given in this paper. A set of I_ds-V_ds curves for the transistor is shown. We find that the smoothing of the potential to account for quantum effects has a strong impact on the electron transport properties, both in transient and steady-state regimes. We also show results for the impact that impurity and surface-roughness scattering mechanisms have on the average velocity of the carriers in the channel and the current flowing through the device. It was found that time-scales as short as 0.1-0.2 ps are enough to reach a steady-state channel electron average velocity     

GaAs图形衬底上InAs量子点生长停顿的动力学蒙特卡罗模拟

采用动力学蒙特卡罗模拟方法对GaAs图形衬底上自组织生长InAs量子点的停顿过程进行了研究．用衬底束缚能的表面分布模拟衬底图形，考察生长之后的停顿时间对量子点形成的影响．结果表明，合适的停顿时间使图形衬底上的量子点分布更趋规则化，对量子点的定位生长有积极的影响．     

Quantum mechanical effects on noise properties of nanoelectronic devices: application to Monte Carlo simulation

A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach.     

Monte Carlo analysis of the carrier relaxation processes in linear and parabolic-GRINSCH quantum well laser structures

The carrier relaxation process is widely acknowledged to have a strong bearing on the modulation limit of quantum well lasers. As a first and crucial step toward achieving a better understanding of this phenomenon, we have developed a numerical technique to study such processes in graded-index separate confinement heterostructure quantum well laser structures having an arbitrary grading profile. We base our approach on ensemble Monte Carlo simulation of the carrier transport in the 3-D graded-index region and in the 2-D quantum well. We also introduce a technique to handle the carrier capture and re-emission processes within the Monte Carlo method. The results obtained from our calculations for a number of structures with quantum well sizes 50-100 Å indicate that the overall carrier capture time is about 5-7.5 ps under low injection condition for the linearly graded structures, and significantly longer for the parabolically graded structures. On the other hand, the carrier capture efficiency is found to be higher for the parabolic graded-index structures. We also compare our calculations to published experiments and find good agreement     

Complete Monte Carlo RF analysis of “real”short-channel compound FET's

A comprehensive RF analysis technique based on ensemble Monte Carlo (EMC) simulation of compound FET's with realistic device geometry is presented. Y-parameters are obtained through Fourier transformation of the EMC transients in response to small changes in the terminal voltages. The terminal currents are statistically enhanced and filtered to allow for reliable y-parameters extraction. Improved analytic procedure for extracting the intrinsic device small-signal circuit components is described. As a result, stable y-parameters and reliable circuit components can he extracted for the whole range of device operation voltages. Parasitic components like contact and gate resistances are included in the y-parameters at a post processing stage to facilitate the forecast of the performance figures of merit of real devices. The developed RF technique has been applied in the EMC simulation of pseudomorphic HEMT's (pHEMT's) fabricated at the Glasgow Nanoelectronics Research Center. Good agreement has been achieved between the simulated and measured small-signal circuit components and performance figures of merit     

In-plane transport properties of Si/Si1-xGexstructure and its FET performance by computer simulation

Transport properties of ungated Si/Si_1-xGe_x are studied by an ensemble Monte Carlo technique. The device performance is studied with a quantum hydrodynamic equation method using the Monte Carlo results. The phonon-scattering limited mobility is enhanced over bulk Si, and is found to reach 23000 cm²/Vs at 77 K and 4000 cm²/Vs at 300 K. The saturation velocity is increased slightly compared with the bulk value at both temperatures. A significant velocity overshoot, several times larger than the saturation velocity, is also found. In a typical modulation-doped field-effect-transistor, the calculated transconductance for a 0.18 μm gate device is found to be 300 mS/mm at 300 K. Velocity overshoot in the strained Si channel is observed, and is an important contribution to the transconductance. The inclusion of the quantum correction increases the total current by as much as 15%     

Intersubband dynamics in modulation doped quantum wells

A theoretical investigation of the dynamics of intersubband transitions in modulation doped multiple narrow GaAs / Al_xGa_1−xAs quantum well structures by emission of GaAs (well) and Al_xGa_1−xAs (barrier) slab and interface mode polar optical phonons is presented. Photo-excited carrier behavior is interpreted via Monte Carlo simulations which predict long time constants for electron relaxation.     

Carrier dynamics studies through free-carrier absorption: a MonteCarlo study for silicon

Monte Carlo based computer simulations normally used for transport studies in semiconductors are extended and used to study free-carrier absorption of subbandgap radiation in semiconductors. The approach is applied to n-type silicon where we find very good agreement with experimental results and calculations based on quantum electrodynamics. The computer simulation method also allows us to study free-carrier absorption in semiconductors with a dc bias. We solve the classical transport equation to show that the absorption coefficient in the presence of a dc bias can be used to obtain information on the carrier temperature, momentum relaxation time, as well as energy relaxation time. Monte Carlo studies show this to be the case. Thus, we show that important carrier dynamics properties can be obtained from long-wavelength free-carrier absorption studies done on samples with a dc bias     

A Fast Stroud-Based Collocation Method for Statistically Characterizing EMI/EMC Phenomena on Complex Platforms

A fast stochastic collocation method for statistically characterizing electromagnetic interference and compatibility (EMI/EMC) phenomena on electrically large and loaded platforms is presented. Uncertainties in electromagnetic excitations and/or system geometries and configurations are parameterized in terms of random variables having normal or beta probability density functions. A fast time-domain integral-equation-based field-cable-circuit simulator is used to perform deterministic EMI/EMC simulations for excitations and/or system geometries and configurations specified by Stroud integration rules. Outputs of these simulations then are processed to compute averages and standard deviations of pertinent observables. The proposed Stroud-based collocation method requires far fewer deterministic simulations than Monte Carlo or tensor-product integrators. To demonstrate the accuracy, efficiency, and practicality of the proposed method, it is used to statistically characterize coupled voltages at the feed pins of cable-interconnected and shielded computer cards as well as the terminals of cables situated inside the bay of an airplane cockpit.      

Applied bias slewing in transient Wigner function simulation ofresonant tunneling diodes

The Wigner function formulation of quantum mechanics has shown much promise as a basis for accurately modeling quantum electronic devices, especially under transient conditions. In this work, we demonstrate the importance of using a finite applied bias slew rate (as opposed to instantaneous switching) to better approximate experimental device conditions, and thus to produce more accurate transient Wigner function simulation results. We show that the use of instantaneous (and thus unphysical) switching can significantly impact simulation results and lead to incorrect conclusions about device operation. We also find that slewed switching can reduce the high computational demands of transient simulations. The resonant tunneling diode (RTD) is used as a test device, and simulation results are produced with SQUADS (Stanford QUAntum Device Simulator)     

A suppression mechanism of Auger recombination effects in strainedquantum wells induced by local negative curvature of the energy bandstructure

An analytical method has been developed to calculate distribution of carriers that undergo CHHS Auger recombinations in semiconductors. From this approach, it is further discovered that holes with a local negative effective mass are, statistically, not favored in the CHHS Auger recombination process. As extended regions in valence subbands of compressively strained quantum well structures possess a negative curvature-and thus a local negative hole effective mass-this mechanism is identified to be a significant factor that suppresses Auger recombination effects in compressively strained quantum well laser diodes. This suppression mechanism is also observed and confirmed by recent Monte Carlo calculation results