Graphene has been recently reported to have a damage threshold high enough to allow for the interaction with ultrashort laser pulses of intensities above 1013 W/cm2. It is natural to explore if this situation to what extend the laser pulse is able to induce the highly non-linear dynamics that gives rise to high harmonic generation. We perform the exact numerical integration of the set of coupled two-level equations that describe the valence-to-conduction band transitions by a laser pulse, at any point in the reciprocal space. We analyze the dynamics of the excitation to the conduction band, and the spectra of the harmonics produced. We show that harmonic radiation is produced by interband as well as intraband transitions, these later resulting from parametric oscillation. We also analyze the temporal characteristics of the harmonic emission.
Double Gate Metal-Oxide-Semiconductor Field-Effect-Transistors (DG MOSFETs) are one of the most promising candidates for future CMOS applications in order to comply with the ITRS requirements. Vertical quantum confinement plays a very important role in these devices when the active layer is below 10 nm, and it can modify significantly the performance of the transistors due to the reduction in the inversion layer population and the modification of transport conditions inside the active zone. Starting from an analysis of the results obtained within a semi-classical framework, we present the discussion of the dynamic and noise results when the effective potential approach is considered for the description of quantum effects in a particle-based Monte Carlo simulator. The main static and dynamic figures of merit are investigated, together with the intrinsic noise sources, thus allowing to provide a full comprehension of the inner physics of the devices and elucidating the consequences of quantum mechanical space-quantization effects (like charge repulsion from the gate-oxide boundaries). Results show that neglecting quantum phenomena leads to an important overestimation of gate capacitance and device transconductance and an underestimation of induced gate noise at RF and microwave frequency ranges.
In this work, we have performed an investigation of the consequences of dowscaling the bulk MOSFET beyond the 100 nm range by means of a particle-based Monte Carlo simulator. Taking a 250 nm gate-length ideal structure as the starting point, the constant field scaling rules (also known as “classical” scaling) are considered and the high-frequency dynamic and noise performance of transistors with 130 nm, 90 nm and 60 nm gate-lengths are studied in depth. The analysis of internal quantities such as electric fields, velocity and energy of carriers or conduction band profiles shows the increasing importance of electrostatic two-dimensional effects due to the proximity of source and drain regions even when the most ideal bias conditions are imposed. As a consequence, a loss of the transistor action for the smallest MOSFET and the degradation of the most important high-frequency figures of merit is observed. Whereas the comparative values of intrinsic noise sources (SID, SIG) are improved when reducing the dimensions and the bias voltages, the poor dynamic performance yields an overall worse noise behaviour than expected (especially for Rn and Gass), limiting at the same time the useful bias ranges and conditions for a proper low-noise configuration.
Due to the enormous industrial interest of the SOI MOSFET technology, a proper understanding of the physics underlying the behavior of these devices is necessary in order to optimize their high frequency performance. In this work, we study the static, dynamic and noise characteristics of FDSOI MOSFET’s by means of numerical simulations validated by comparison with experimental data. For this purpose, we use a 2D Ensemble Monte Carlo simulator, taking into account, in an appropriate manner, the physical topology of a fabricated 0.25 μm gate-length FDSOI transistor. Important effects appearing in real transistors, such as surface charges, contact resistances, impact ionization phenomena and extrinsic parasitics are included in the simulation. This allows to accurately reproduce the experimental behavior of static and dynamic parameters (output and transference characteristics, gm/ID ratio, capacitances, etc.). Moreover, results are explained by means of internal quantities such as concentration, velocity or energy of carriers. The results of the Monte Carlo simulations for the typical four noise parameters (NFmin, Gass, Rn, \Gamma opt) of the 0.25 μm FDSOI MOSFET also show an exceptional agreement with experimental data. Once the reliability of the simulator has been confirmed, a full study of the noise characteristics of the device (noise sources, drain spectral densities, α, β and C parameters, etc.) is performed. Taking advantage of the possibilities of the Monte Carlo method as a pseudo-experimental approach, the influence on these noise characteristics of the variation of some geometry parameters (i.e., downscaling the gate length, thickness of the active layer or inclusion of HALO regions) is evaluated an interpreted in terms of microscopic transport processes.