Nabil S. Mansour

Monte Carlo calculation of electron impact ionization in bulk InAs and HgCdTe

We present calculations based on an ensemble Monte Carlo simulation of the electron impact ionization rate in bulk InAs and Hg0.70Cd0.30Te at 77 K. The Monte Carlo calculation includes an analytic nonparabolic model of the conduction band, all of the dominant scattering mechanisms, and a nonparametrized model of the impact ionization rate. Calculations are first made of the ionization rate in bulk InAs and are compared to both experiment and previous Monte Carlo investigations. Updated material parameters are used as well as calculated values of the threshold energy and the ionization probability in the InAs simulation. Good agreement with previous Monte Carlo studies is achieved. Using a similar model, the electron ionization rate in bulk Hg0.70Cd0.30Te is studied. To our knowledge, this is the first study either theoretically or experimentally of electron impact ionization in long wavelength (5 μm) band‐gap HgCdTe.

Ensemble Monte Carlo study of electron transport in degenerate bulk GaAs

A theoretical investigation is presented of the effect of ionized impurity scattering, electron‐electron interaction, and degeneracy, both separately and collectively, on the bulk steady‐state transport properties of degenerate GaAs. The calculations are performed using an ensemble Monte Carlo simulation that includes an analytic nonparabolic formulation of the three principal valleys in the conduction band and all of the important phonon scattering mechanisms. It is found that the overall velocity‐field characteristic is determined primarily by the action of electron‐plasmon scattering at high electric fields (near the intervalley threshold field). At lower fields, below which the electrons are not heated to the threshold energy for plasmon emission, ionized impurity scattering is the most dominant mechanism. In addition the effects of degeneracy are also important throughout. Only the short‐range electron‐electron interaction has little effect on the velocity‐field curve owing to the fact that it does n...

Simulation of advanced semiconductor devices using supercomputers

Abstract The current generation of advanced semiconductor devices often exhibit nonlinear effects which require numerical approaches to their simulation. In addition to nonlinearities, the accurate description of the behavior of ever increasingly small devices, as well as those which contain heterostructures or superlattices, demands extraordinarily complex techniques which typically overwhelm most computational environments. Under these conditions, the supercomputer provides the only reasonable means by which the behavior of advanced semiconductor devices can be examined in detail. In this paper, we present a discussion of computational techniques and their application to modeling avalanching semiconductor devices within a supercomputer environment. Specifically, issues such as velocity and current estimators, bipolar simulation, temporal response, and subensemble simulation will be addressed. Calculated results are presented for representative systems to illustrate the use of these estimators.

COMPARISON OF DIFFERENT FORMULATIONS OF THE ELECTRON-PLASMON SCATTERING RATE AND THE DISPERSION RELATION ON BULK SEMICONDUCTOR TRANSPORT

We compare the effect of two different formulations of the electron‐plasmon scattering rate, the electron‐field and electron‐electron models, as well as different formulations of the dispersion relationship on the calculated bulk transport properties of degenerate GaAs. The calculations are performed using an ensemble Monte Carlo simulation which includes an analytical nonparabolic model of the principle valleys in the conduction band, and all of the dominant scattering mechanisms. It was previously found that the functional form of the dispersion relationship significantly alters the magnitude of the electron‐plasmon scattering rate. As a consequence, the steady‐state velocity‐field characteristics are also significantly altered by as much as ∼40% by the choice of the dispersion relation. It is further found that the choice of either the electron‐electron or electron‐field model does not by itself significantly alter the calculated results. Therefore, either model can be used to describe the effects of e...

Theory of the electron‐plasmon interaction in Monte Carlo calculations through the direct solution of the Poisson equation

Ensemble Monte Carlo calculations of the steady‐state electron drift velocity in degenerate bulk GaAs using a self‐consistent algorithm specially tailored to directly include the electron‐plasmon interaction are presented. The critical issues implicit in the direct approach are the mesh size, charge assignment to the mesh nodes, interpolation of the field at the particle location, and the frequency with which the solution of the Poisson equation is updated. All of these factors determine the stability of the system, the accuracy, and the computational time required in the calculation. Comparison is made to quantum mechanically based techniques in which the electron‐plasmon interaction is treated as an additional scattering mechanism. It is found that the steady‐state electron drift velocity in bulk degenerate GaAs calculated using the semi‐classical approach for the electron‐plasmon interaction is significantly less than that calculated assuming no electron‐plasmon interaction is present. The steady‐state...

Theoretical investigation of different formulations of the electron-plasmon interaction under transient conditions

We present a comparison of two different methods of including the electron‐electron long‐range interaction on the dynamics of hot electrons in degenerate GaAs under transient conditions in two different hot electron transistor structures of 60‐ and 120‐nm base widths, respectively. The first approach is quantum mechanically based while the second follows a semiclassical prescription. The calculated energy spectrum, velocity distribution, and percentage of injected carriers collected in the hot electron transistors are determined under three different conditions: the inclusion of the plasmon interaction through the quantum‐mechanical formulation, the inclusion of the plasmon interaction through the semiclassical technique, and with no plasmon interaction. The calculated energy spectrums within the two plasmon models are qualitatively similar. They differ only by the extent to which the peaks are broadened and the absolute ratio of collected to injected carriers. Because of the very different energy relaxat...

Theoretical study of a potential low-noise semimetal-based avalanche photodetector

The authors present a theoretical analysis of a possible avalanching photodetector (APD)-based on II-VI compound semiconductors. Each unit cell is composed of a HgTe layer, or a similar semimetal, sandwiched between two layers of CdTe and HgCdTe or similar semiconducting materials. The barrier layers are graded so that the leading barrier height is just high enough to eliminate the thermionic emission dark current out of the well. The use of a semimetal within the well has a distinct advantage over a semiconductor, which is that the ionization process is essentially an interband mechanism since the confined carriers within the well lie within the overlapping conduction and valence bands. As a result, the concentration of target carriers is virtually inexhaustible as in a conventional interband device. >

Theoretical study of potential ultralow noise, confined state photodetectors

A review of the basic issues implicit in the design of confined state photodetectors is presented. The basic device structure of a confined state photomultiplier consists of repeated unit cells each comprised of a narrow-gap semiconductor layer sandwiched between barrier layers of wider band-gap material. Gain in these structures is derived through carrier multiplication via impact excitation of confined electrons out of the narrow-gap semiconductor layer. Different device designs are considered in an attempt to maximize the device gain at minimum dark current. In some implementations, the barrier layers are chosen to be graded such that the leading edge discontinuity is at least twice that at the trailing edge of the well forming an asymmetric well design. We find that an asymmetric well design offers a much higher impact excitation of electrons confined within the well at a lower operating voltage than a symmetric well design, however, at the expense of increased dark current. Quantum versus classical confinement of the electrons within the well is also investigated. Though the ionization rate within the classical confinement design is less under comparable conditions to that in the quantum confinement design, the dark current is much less within the classical structure than in the quantum structure, giving a higher excitation-rate-to-dark-current ratio. The gain and dark current are investigated in structures made from GaN/AlGaN, HgTe/HgCdTe, and GaAs/AlGaAs.

Monte Carlo based calculations of hole transport including the hole‐plasmon interaction in degenerate bulk GaAs

A theoretical study of the effect of the hole‐plasmon interaction on the calculated bulk transport properties of degenerate GaAs is presented. The calculations are performed using an ensemble Monte Carlo simulation which includes the full details of the heavy, light, and split‐off valence bands derived from a k○p calculation as well as all of the dominant hole‐phonon scattering mechanisms. The hole‐plasmon interaction is treated as a separate scattering mechanism and is computed to first order in perturbation theory. The plasmon dispersion relation is determined numerically by finding the zeroes of the dielectric function assuming hole occupation within both the heavy‐ and light‐hole bands. The hole‐plasmon scattering rate is computed self‐consistently during the course of the Monte Carlo simulation as a function of the hole concentration and carrier temperature within the heavy‐hole and light‐hole bands. It is found that at degenerate hole concentrations, the hole‐plasmon scattering rate is much smaller ...

Theoretical study of potential ultralow-noise confined-state photodetectors

The purpose of this paper is to present a review of the basic issues implicit in the design of confined state photodetectors. The basic device structure consists of repeated unit cells each comprised of a narrow gap semiconductor layer sandwiched between barrier layers of wider band gap material. Gain in these structures is derived through carrier multiplication via impact excitation of confined electrons out of the narrow gap semiconductor layer. Different device designs are considered in an attempt to maximize the device gain at minimum dark current. In some implementations, the barrier layers are chosen to be graded such that the leading edge discontinuity is at least twice that at the trailing edge of the well forming an asymmetric well design. It is found that an asymmetric well design offers a much higher impact excitation of electrons confined within the well at lower operating voltage than a symmetric well design however at the expense of increased dark current. Quantum versus classical confinement of the electrons within the well is also investigated.