Wolfgang  Porod

Guest Editorial

A theoretical (using rate equations) and experimental study of the nonlinear dynamicsof a distributed feedback multiple quantum well laser diode is presented. The analysis isperformed under direct modulation. Period doubling and period tripling are identifiedin both the measurements and simulations. Period doubling is found over a wide rangeof modulation frequencies in the laser. Computational results using rate equations showgood agreement with the experimental results.

Stephen  Bennett 

Christopher M. Snowden

Stavros  Iezekiel

Rate Equation Modelling of NonlinearDynamics in Directly Modulated MultipleQuantum Well Laser Diodes

We present a multi-mode drift-diffusion equation as reformulation of the Boltzmann
equation in the discrete momentum space. This is shown to be similar to the conventional drift-diffusion equation except that it is a more rigorous solution to the Boltzmann equation because the current and carrier densities are resolved into M×1 vectors, where M is the number of modes in the discrete momentum space. The mobility and diffusion coefficient become M×M matrices which connect the M momentum space modes. This approach is demonstrated by simulating electron transport in bulk silicon.

K. Banoo

F. Assad

M. S. Lundstrom

Formulation of the Boltzmann Equation as a Multi-Mode
Drift-Diffusion Equation

Electron transport properties of quantum wires in the presence of a periodically
modulated magnetic field are investigated. For a short modulated wire, we find dips in
conductance just below each mode threshold. The conductance dips are quite robust at
low temperature. Increasing the number of periods of magnetic modulation can lead to
the formation of minibands and gaps. The differences between the one dimensional (1D)
electric superlattice and 1D magnetic superlattice are discussed. We also consider the
spatial distributions of currents, which show dramatic differences between the magnetic
superlattices and electric ones.

Zhen-Li Ji

D. W. L. Sprung

Electron Transport In One-Dimensional
Magnetic Superlattices

Molecular Dynamics (MD) is a powerful tool for the atomistic understanding of longrangestress-mediated phenomena, phonon properties, and mechanical failure ofnanostructures. For realistic modeling of nanostructures, however, the scope ofsimulations must be extended to large system sizes, long simulated times, and complexrealism. We have developed new multilevel algorithms and physical models encompassingmultiple levels of abstraction: i) space-time multiresolution schemes; ii) adaptivecurvilinear-coordinate load balancing; iii) hierarchical dynamics via a rigid-body/implicit-integration/normal-mode approach; iv) variable-charge MD based on electronegativityequalization; and v) multilevel preconditioned conjugate gradient method.Fuzzy clustering is used to facilitate the seamless integration of the multiple levels ofabstraction.

Aiichiro  Nakano

Rajiv K. Kalia

Priya  Vashishta

Multilevel Algorithms for Large-scope Molecular DynamicsSimulations of Nanostructures on Parallel Computers

Photon recycling is examined as an explanation for the observed large carrier lifetimes inan InP/InGaAs photodiode. This effect extends the effective carrier lifetime within adevice by re-absorbing a fraction of the photons generated through radiative band-tobandrecombination events. In order to predict the behavior of this carrier generation,photon recycling has been added to our two-dimensional macroscopic device simulator,STEBS-2D. A ray-tracing preprocessing step is used to map all of the possibletrajectories and absorption of various wavelengths of emitted light from eachoriginating node within the device. The macroscopic simulator uses these data todetermine the spatial location of the re-absorbed radiation within the geometry of thedevice. By incorporating the ray tracer results with the total quantity and spectralcontent of recombined carriers at each node within the simulation, the recycledgeneration rate can be obtained. A practical application of this model is presented wherethe effects of photon recycling are used as a possible explanation of the discrepancybetween the theoretically predicted and experimentally observed radiative recombinationrate in a double heterostructure photodetector.

Joseph W. Parks

Kevin F. Brennan

Arlynn W. Smith

Numerical Examination of Photon Recycling as anExplanation of Observed Carrier Lifetime in DirectBandgap Materials

In this paper we described a complete methodology to extract the RF performance of&#8216;real&#8217; compound FETs from time domain Ensemble Monte-Carlo (EMC) simulationswhich can be used for practical device design. The methodology is based on transientfinite element EMC simulation of realistic device geometry. The extraction of theterminal current is based on the Ramo-Shockley theorem. Parasitic elements like thegate and contact resistances are included in the RF analysis at the post-processing stage.Example of the RF analysis of pseudomorphic HEMTs illustrates our approach.

S.  Babiker

A.  Asenov

N.  Cameron

S. P. Beaumont

J. R. Barker

Complete RF Analysis of Compound FETs Basedon Transient Monte Carlo Simulation

By adopting the solution method for the BTE based on the spherical-harmonicsexpansion (SHE) &#91;1&#93;, and using the full-band structure for both the electron and valenceband of silicon &#91;2&#93;, the temperature dependence of a number of scattering mechanismshas been modeled and implemented into the code HARM performing the SHE solution.Comparisons with the experimental mobility data show agreement over a wide range oftemperatures. The analysis points out a number of factors from which the difficultiesencountered in earlier investigations seemingly originate, particularly in the case of holemobility.

Susanna  Reggiani

Maria Cristina Vecchi

Massimo  Rudan

Temperature Dependence of the Electron and HoleScattering Mechanisms in Silicon Analyzed through aFull-Band, Spherical-Harmonics Solution of the BTE

Electron transport properties in SiC quantized inversion layers have been studied bymeans of a Monte Carlo procedure. It has been observed that the contribution of polaropticalphonon scattering produces a significant influence of the effective-electric fieldon the high longitudinal field transport regime, this being the main difference of SiCwith respect to standard Si inversion layers. The energy- and momentum-relaxationtimes have been calculated and the results suggest that electron velocity overshooteffects are less important than in Si MOSFETs. The electron mobility is not verydifferent from their silicon counterparts, but the saturation velocity is higher.

F.  G&#225;miz

J. B. Rold&#225;n

J. A. L&#243;pez-Villanueva

A &#946;-SiC MOSFET Monte Carlo Simulator IncludingInversion Layer Quantization

Although impact ionization feedback is recognized as an important current multiplicationmechanism, its importance as a carrier heating mechanism has been largelyoverlooked. This work emphasizes the inclusion of impact ionization feedback in MonteCarlo device simulations, and its implications for carrier heating in sub-micron CMOSand EEPROM technologies.

Jeff D. Bude

Monte Carlo Simulations of Impact Ionization Feedback in MOSFET Structures

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