Monte Carlo simulation of electron velocity in degenerate GaAs

A calculation of the electron velocity in heavily doped GaAs has been performed. A model to account for the LO phonon-plasmon coupling effects is proposed in a full Monte Carlo simulator; we believe this is the first time this fact has been tried out. Nonequilibrium screening effects are considered in the simulation. The Pauli exclusion principle is extended to the hot electron regime by the use of the electron temperature, which is calculated self consistently from the mean energy. A direct comparison with experimental velocities is made to show the accuracy of the simulation at both 77 and 300 K. Comparisons with simpler Monte Carlo models are also presented to illustrate the influence of the different effects considered     

Monte Carlo simulation of noise in GaAs semiconductor devices

The Monte Carlo method has been used to calculate the noise in GaAs resistors where finite-size effects are important, being from 0.5 to 1.5 μm in length. The results agree qualitatively with experimental noise measurements performed on similar devices. Monte Carlo noise calculations have also been conducted for Schottky barrier diodes. A method for conducting full-device Monte Carlo simulations of these diodes has been employed. Schottky barrier diodes with both 0.12 and 1.0 μm epitaxial layers were modeled, and the calculated noise is in agreement with experiment throughout a wide range of bias voltages, both when shot noise and when excess noise predominate. Two different methods of calculating the noise current have been compared     

Monte Carlo simulation of the GaAs permeable base transistor

A two-dimensional multiparticle Monte Carlo (MC) method for the solution of the Boltzmann transport equation has been implemented and the results compared with the conventional drift-diffusion equation solution obtained for both a uniformly doped and an n⁺-n-n⁺GaAs permeable base transistor structure. Improved high-frequency performance is predicted by the MC simulation. Two-dimensional boundary conditions for a "regional" MC analysis have been applied to reduce the computer time that would be spent largely in analyzing the device retarding field region and the neutral regions of the device. The dc parameters, I-V characteristics, and unity current gain-frequency (fT) are discussed. In the n⁺-n-n⁺doped structure, a cooling effect was found that significantly enhances the device frequency performance by reducing the satellite valley population of electrons.     

Monte Carlo particle simulation of a GaAs short-channel MESFET

A Monte Carlo particle simulation of a 0.25 ?m-long gate (and 0.25 ?m-long channel) GaAs MESFET having a practical doping density and sitting on a substrate is carried out. Extremely high values of gm and Idss of 643 mS/mm and 5.35 mA/20 ?m were obtained. The near-ballistic nature of the electron transport in the FET was confirmed.     

Monte Carlo simulation of Schottky diodes operating under terahertz cyclostationary conditions

We report Monte Carlo simulations of the current response and noise spectrum in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) operating under periodic large-signal conditions in the forward bias region. Due to the rather thin depletion region and heavy doping of these diodes, we find that the returning carrier resonance is shifted well above the terahertz region, so that the low-frequency noise plateau extends over the terahertz region. Here, frequency multiplication and mixing can take place at noise levels equal or below than that of full shot noise. We show that the signal-to-noise ratio of these SBDs is definitely superior to that of bulk semiconductors exploiting velocity-field nonlinearity.     

Simulation of Schottky barrier MOSFETs with a coupled quantuminjection/Monte Carlo technique

A full-band Monte Carlo device simulator has been used to analyze the performance of sub-0.1 μm Schottky barrier MOSFETs. In these devices, the source and drain contacts are realized with metal silicide, and the injection of carriers is controlled by gate voltage modulation of tunneling through the source barrier. A simple model treating the silicide regions as metals, coupled with an Airy function approach for tunneling through the barrier, provides injecting boundary conditions for the Monte Carlo procedure. Simulations were carried out considering a p-channel device with 270 Å gate length for which measurements are available. Our results show that in these structures there is not a strong interaction with the oxide interface as in conventional MOS devices and carriers are injected at fairly wide angles from the source into the bulk of the device. The Monte Carlo simulations not only give good agreement with current-voltage (I-V) curves, but also easily reproduce the subthreshold behavior since all the computational power is devoted to simulation of channel particles. The simulations also clarify why these structures exhibit a large amount of leakage in subthreshold regime, due to both thermionic and tunneling emission. Computational experiments suggest ways to modify the doping profile to reduce to some extent the leakage     

Monte Carlo simulation of AlGaAs/GaAs heterojunction bipolar transistors

A first demonstration of one-dimensional Monte Carlo simulations of AlGaAs/GaAs heterojunction bipolar transistors is reported. The electron motion is solved by a particle model, while the hole motion is solved by a conventional hydrodynamic model. It is shown that the compositional grading of AlxGa1-xAs in the base region is effective to cause the ballistic acceleration of electrons in the base region, resulting in a high collector current density of above 1 mA/µm². The current-gain cutoff frequency fT reaches 150 GHz if the size of a transistor is properly designed. Also shown is the relation between the device performances and the electron dynamics investigated.     

Monte Carlo particle simulation of GaAs submicron n+-i-n+ diode

Monte Carlo particle simulation of a GaAs submicron n+-i-n+ diode showed that the electron transport in the diode is almost ballistic in nature, so long as the electron energy is below 0.36 eV. A maximum electron velocity of 1 × 108 cm s?1 was observed at certain conditions. Effects of the electron backscattering from the anode n+-layer are also discussed.     

Modeling for an AlGaAs/GaAs heterostructure device using Monte Carlo simulation

Two-dimensional electron gas behavior in an AlGaAs/GaAs heterostructure FET has been analyzed using the Monte Carlo method. In the channel region, it is assumed that the electrons are subjected to a two-dimensional scattering process. In the other regions, three-dimensional scattering rates are assumed. It is predicted that, in an actual device with 1.20-µm gate length, the transconductance of 250 and 450 mS/mm can be attained at 300 and 77 K, respectively. More efficient performance is possible with improvements in the device structure.     

Investigation of Ti-Ge/GaAs Schottky barrier contacts

The effect of germanium content in a titanium film, as well as treatment methods and conditions, on the Schottky barrier height (φ_b) and the ideality factor (n) for Ti-Ge / GaAs contacts were investigated. It is shown that photon treatment provides better contacts than thermal treatment.     

Monte Carlo harmonic-balance and drift-diffusion harmonic-balanceanalyses of 100-600 GHz Schottky barrier varactor frequency multipliers

To date, high frequency multipliers have been designed and analyzed using harmonic-balance codes incorporating equivalent circuit models for the diodes. These codes, however, are unable to accurately predict circuit performance at frequencies above 100 GHz and do not allow a means for studying the physics of electron transport. In order to analyze these high frequency Schottky doublers, a novel harmonic-balance technique has been integrated into a drift-diffusion numerical simulator and, for the first time, a Monte Carlo numerical device simulator. The unification of the numerical device simulator with the harmonic-balance algorithm allows for the self-consistent study of electron transport phenomena as well as the study of device performance in a given circuit. These combined simulators are tested against experimental data and an equivalent circuit model harmonic-balance approach, and yield superior accuracy with respect to the experimental data     

Monte Carlo simulation for electron transport in MESFETs includingrealistic band structure of GaAs

A full band Monte Carlo (FBMC) simulator was developed for electron transport in GaAs MESFETs. As a result of increased scattering rate due to the complicated band structure, the average velocity in the high field region was lower than the analytical band Monte Carlo (ABMC) result. Also, the simulated energy peak was higher than the ABMC result, due to electrons populating the upper bands. Not only due to a limited number of the first conduction band states capable of ionization, but also due to a small mass of the second conduction band, more than 95% of ionization events were shown to occur in the upper bands. The simulated ionization rate lies within the range of experimental results. To our knowledge, this is the first report on the full band two-dimensional (2-D) self-consistent GaAs MESFET simulation     

Computer study on GaAs Schottky barrier IMPATT diodes

Oscillation characteristics of GaAs Schottky barrier IMPATT diodes are studied by computer simulation. For a Schottky barrier-n-n⁺ structure, the Read condition and the just-punch-through condition are found to be optimum with respect to the efficiency and power at 30 GHz. In order to improve the efficiency, a superabrupt doping profile is proposed and a high efficiency of 32 per cent is predicted. Calculation of the frequency dependence of the efficiency shows that GaAs IMPATT diodes still have the potentiality of high efficiency oscillator at 100 GHz and they are a promising microwave source in mm-wave region.     

Monte Carlo simulation of impact ionization rates in InAlAs-InGaAssquare and graded barrier superlattice

The Monte Carlo method is used to analyze impact ionization rates for electrons and holes in a 〈100〉 crystal direction In_0.52Al_0.48As-In_0.53Ga_0.47 As square and graded barrier superlattice. The calculated impact ionization rate ratio α/β is enhanced to more than 10 in a wide barrier and narrow-well square barrier superlattice. This is because the hole ionization rate β is greatly reduced in the narrower well superlattice, while the electron ionization rate α is less sensitive to well and barrier layer thickness. These results are explained by a combination of the ionization dead space effect for the barrier layer and the electron ionization rate enhancement in the well layer due to large conduction band edge discontinuity. Furthermore, it is found that in a graded barrier superlattice, the impact ionization rate ratio α/β is smaller than that for a square barrier superlattice having the same barrier and well thickness. This is due to the occurrence of hole ionization in the narrow bandgap region in graded barriers. The band structure effects on hot carrier energy distribution, as well as impact ionization, are also discussed     

Two-dimensional Monte Carlo simulation of a submicron GaAs MESFET with a nonuniformly doped channel

A two-dimensional-ensemble Monte Carlo program coupled with a program for solving Poisson's equation is used to perform a self-consistent simulation of a GaAs MESFET having a nonuniformly doped (ion-implanted) channel. For V_gs = ?0.5 V and V_ds = 1 V, the simulation yields I_ds = 18 mA/50 μm, g_m = 755 mS/mm and f_T = 230 GHz. The results are compared to those obtained from a conventional 2D device-analysis program which uses static velocity-field characteristics and an empirical expression for low-field mobility versus doping concentration. The currents, transconductance, and cutoff frequency obtained from the Monte Carlo simulation are considerably larger than those obtained from the conventional 2D analysis. This difference is explained by the fact that the conventional device analysis program fails to account for transient transport phenomena.     

Temperature behaviour and compensation of Schottky barrier diode

This paper offers a fresh look into the temperature behaviour and compensation of Schottky barrier diode's radio frequency (RF) resistance. RF resistance of a Schottky diode varies with temperature at conventional fixed current bias as well as fixed voltage bias condition. Here we have proposed “optimum load-line biasing technique” to achieve temperature invariant RF performance of the Schottky diode based RF circuits. Mathematically we have shown and verified by measurements that the proposed technique provides temperature insensitive RF performance over a very wide range of operating temperature. Thus, without any separate temperature sensor and compensation circuits, as used in conventional temperature-compensation schemes, it is possible to achieve temperature invariant RF performance of the Schottky diode based RF circuits.     

Monte Carlo微粒模拟法研究GaAs的NDM

本文用Monte Carlo 微粒模拟法(Particle Simulation)研究了GaAs中导带电子的负微分迁移率NDM(Negative Differential Mobility).电子的起始状态假设按照麦克斯韦律分布在Γ带中.电子作漂移运动时考虑了极性光学波和声学波的谷内、谷间散射.散射后假设定向速度消失,简化了计算.结果表明和实验值符合良好.也和前人计算结果进行了比较.     

A GaAs MESFET Schottky diode barrier height reference circuit

A barrier height reference voltage has been implemented with Schottky diodes in GaAs MESFET technology. It achieves less than 100 ppm/°C drift and can be used to create a reference voltage for source coupled logic, data converters, and as the basis for a variety of biasing circuits. Moderate accuracy is achieved with a circuit topology that reduces the ratio of control amplifier input voltage to reference voltage. The 7×16 mil² circuit achieves 36 dB of supply rejection, draws 700 μA from 5 V, and is implemented in a 20-GHz ion implanted manufacturing process     

Monte Carlo simulation of bipolar transistors

A new approach is proposed to investigate, the limits of validity of the conventional drift-diffusion equation analysis for modeling bipolar transistor structures containing submicrometer dimensions. The single-particle Monte Carlo method is used for the solution of the Boltzmann equation. An electron velocity overshoot of 1.8 times the static saturation velocity has been found for electrons near the base-collector junction of a silicon device. The effect of this velocity overshoot was calculated to enhance the output collector current and reduce the electron transit time by 5 percent for the device structure considered in this work.