Ultrafast carrier relaxation and vertical-transport phenomena in semiconductor superlattices: A Monte Carlo analysis

The ultrafast dynamics of photoexcited carriers in semiconductor superlattices is studied theoretically on the basis of a Monte Carlo solution of the coupled Boltzmann transport equations for electrons and holes. The approach allows a kinetic description of the relevant interaction mechanisms such as intra- miniband and interminiband carrier-phonon scattering processes. The energy relaxation of photoexcited carriers, as well as their vertical transport, is investigated in detail. The effects of the multiminiband nature of the superlattice spectrum on the energy relaxation process are discussed with particular emphasis on the presence of Bloch oscillations induced by an external electric field. The analysis is performed for different superlattice structures and excitation conditions. It shows the dominant role of carrier-polar-optical-phonon interaction in determining the nature of the carrier dynamics in the low-density limit. In particular, the miniband width, compared to the phonon energy, turns out to be a relevant quantity in predicting the existence of Bloch oscillations

On a simple and accurate quantum correction for Monte Carlo simulation

ISSN:1569-8025ISSN:1572-813

Monte-Carlo-Bauelementsimulator fuer Si/SiGe-Heterobipolartransistoren Abschlussbericht

The Monte Carlo simulators for homogeneous Si and MOSFETs, previously developed in the projekt NT 2792 D1, have been extended for the simulation of strained SiGe and n-p-n heterojunction bipolar transistors (HBTs). The new simulators support the technology developments of the project partners in the joint project LOTUS. Analytical band structure models for strained SiGe and scattering by Ge phonons as well as alloy scattering have been included in the model for homogeneous SiGe. In the case of electrons the model has been successfully verified by mobility measurements in strained SiGe. The Monte Carlo simulator for homogeneous SiGe has been applied to generate the transport parameters for the classical device simulators of the project partners. After inclusion of the SiGe model and the extension to position-dependent band structures, stationary and transient simulations of HBTs have been performed with the Monte Carlo device simulator. These simulations are necessary to access the accuracy of the classical device simulators. First clear hints for a poor simulation accuracy of the drift-diffusion model for aggressively scaled SiGe HBTs have been found. (orig.)Available from TIB Hannover: F98B411+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Monte-Carlo-Bauelementsimulator fuer Si/SiGe-Heterobipolartransistoren Abschlussbericht

The Monte Carlo simulators for homogeneous Si and MOSFETs, previously developed in the projekt NT 2792 D1, have been extended for the simulation of strained SiGe and n-p-n heterojunction bipolar transistors (HBTs). The new simulators support the technology developments of the project partners in the joint project LOTUS. Analytical band structure models for strained SiGe and scattering by Ge phonons as well as alloy scattering have been included in the model for homogeneous SiGe. In the case of electrons the model has been successfully verified by mobility measurements in strained SiGe. The Monte Carlo simulator for homogeneous SiGe has been applied to generate the transport parameters for the classical device simulators of the project partners. After inclusion of the SiGe model and the extension to position-dependent band structures, stationary and transient simulations of HBTs have been performed with the Monte Carlo device simulator. These simulations are necessary to access the accuracy of the classical device simulators. First clear hints for a poor simulation accuracy of the drift-diffusion model for aggressively scaled SiGe HBTs have been found. (orig.)Available from TIB Hannover: F98B411+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

JESSI-BLR. Advanced technology for 0.25 #mu#m CMOS and below Subproject: device simulation. Topic: hot carriers, energy transport and thermal diffusion. Final report

The 2D Monte Carlo Device Simulator as previously developed in the project NT 2707 A4 has been substantially improved for a more sophisticated treatment of Si MOSFETs with extremely short channel lengths. The analytical bandstructure being composed of several bands for electrons and holes enables the description of the density-of-states up to energies of 3eV and 5eV. All scattering mechanisms, especially band-to-band impact ionization, were described in a consistent way by analytical formulas. The stand-alone simulator for electrons in inversion layers shows good agreement with experimental data in the linear and nonlinear transport regime. The new device simulator was successfully applied for the simulation of NMOSFETs with channel lenghts between 0.7#mu#m and 0.1#mu#m and a 0.5#mu#m-PMOSFET. In addition to the usual discussion of drain-and substrate current the distribution of high energetic carriers and secondary generated holes as well as the injection of hot electrons into the gate oxide were investigated. Especially the simulation of high energetic carriers required the extension of the variance reducing Multiple Refresh technique to applications in full phase space. For the comparison with traditional simulation methods a generalized system of macroscopic balance equations and transport coefficients has been developed without using the phenomenological relaxation time ansatz. (orig.)Der aus dem Vorgaengerprojekt NT 2707 A4 zur Verfuegung stehende 2D Monte-Carlo-Bauelementsimulator wurde mit dem Ziel einer verbesserten Beschreibung von Si-MOSFETs mit extrem kurzen Kanallaengen weiterentwickelt. Die fuer Elektronen und Loecher benutzte analytische Formulierung der Bandstruktur besteht aus mehreren Baendern und reproduziert die Zustandsdichte bis zu Energien von 3eV bzw. 5eV. Alle Streuprozesse, insbesondere die Band-Band-Stossionisation, konnten dazu konsistent durch eine analytische Formulierung beschrieben werden. Mit dem eigenstaendigen Simulator fuer Elektronen in Inversionskanaelen gelang erstmals eine erfreulich gute Reproduktion der experimentellen Daten des linearen und nichtlinearen Transports. Der erweiterte Bauelementsimulator wurde fuer die Simulation von NMOSFETs mit effektiven Kanallaengen von 0.7#mu#m bis 0.1#mu#m sowie eines 0.5#mu#m-PMOSFET erfolgreich eingesetzt. Neben den ueblichen Betrachtungen zum Drain- und Substratstrom wurde die Verteilung der hochenergetischen Ladungstraeger und der sekundaer generierten Loecher sowie die Injektion von hochenergetischen Elektronen in das Gate-Oxid untersucht. Dazu war eine Erweiterung der varianzreduzierenden Multiple-Refresh-Technik auf den vollstaendigen Phasenraum notwendig. Fuer den Vergleich mit konventionellen Simulationsmethoden wurde ein verallgemeinertes System von makroskopischen Bilanzgleichungen mit dazu gehoerigen Transportkoeffizienten ohne Annahme des phaenomenologischen Relaxationszeitansatzes erarbeitet. (orig.)SIGLEAvailable from TIB Hannover: F94B0787+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Comparison of Monte Carlo Transport Models for Nanometer-Size MOSFETs

This paper presents the results of a comparison among five Monte Carlo device simulators for nano-scale MOSFETs. These models are applied to the simulation of the I-V characteristics of a 25 nm gate-length MOSFET representative of the high-performance transistor of the 65 nm technology node. Appreciable differences between the simulators are obtained in terms of simulated ION. These differences are mainly related to different treatments of the ionized impurity scattering (IIS) and pinpoint a limitation of the available models for screening effects at very large carrier concentrations

NEGF Simulations of the effect of strain on scaled double gate NanoMOSFETs

The effect of biaxial strain on double gate (DG) nanoscaled Si MOSFET with channel lengths in the nanometre range is investigated using Non-Equilibrium Green’s Functions (NEGF) simulations. We have employed fully 2D NEGF simulations in order to answer the question at which body thickness the effects of strain is masked by the confinement impact. Following ITRS, we start with a 14 nm gate length DG MOSFET having a body thickness of 9 nm scaling the transistors to gate lengths of 10, 6 and 4 nm and body thicknesses of 6.1, 2.6 and 1.3 nm. The simulated I D–V G characteristics show a 6% improvement in the on-current for the 14 nm gate length transistor mainly due to the energy separation of the Δ valleys. The strain effect separates the 2 fold from the 4 fold valleys thus keeping mostly operational transverse electron effective mass in the transport direction. However, in the device with an extreme body thickness of 1.3 nm, the strain effect has no more impact on the DG performance because the strong confinement itself produces a large energy separation of valleys