Jean-Luc Thobel

Dynamic modeling of a midinfrared quantum cascade laser

Based on a three-level rate equations model, we analyze through numerical simulations the population and photon number dynamics present within the cavity of a midinfrared quantum cascade laser. We find in particular that the injection current influences significantly the electron number dynamics trajectory. In addition, the equations that allow for the determination of the turn-on delay (tth) and buildup (Δt) times are derived within the premises of our model in the most general case. The effects of the spontaneous emission factor β on Δt are also explored.

Analysis of the high-frequency performance of InGaAs∕InAlAs nanojunctions using a three-dimensional Monte Carlo simulator

We report results from the investigation of the intrinsic high-frequency (HF) behavior of three-terminal junctions based on InGaAs∕InAlAs heterostructures, using a well-calibrated three-dimensional semiclassical ensemble Monte Carlo simulation model. The simulator incorporates a more realistic surface charge model, designed specifically for HF simulations. A full analysis of the dynamics of electron transport in the devices is performed and a prediction of its intrinsic HF performance is presented. Simulation results demonstrate how these devices may be suitable for applications in the terahertz frequency range. Most importantly, we illustrate the important role played by surface charge effects in this frequency regime. The necessity of considering these effects as a key design factor for the development of future nanojunction structures operating in the terahertz regime is therefore discussed.

Self-consistent electrothermal Monte Carlo simulation of single InAs nanowire channel metal-insulator field-effect transistors

Electron transport and self-heating effects are investigated in metal-insulator field-effect transistors with a single InAs nanowire channel, using a three-dimensional electrothermal Monte Carlo simulator based on finite-element meshing. The model, coupling an ensemble Monte Carlo simulation with the solution of the heat diffusion equation, is carefully calibrated with data from experimental work on these devices. This paper includes an electrothermal analysis of the device basic output characteristics as well the microscopic properties of transport, including current-voltage curves, heat generation and temperature distributions, and electron velocity profiles. Despite the low power dissipation, results predict significant peak temperatures, due to the high power density levels and the poor thermal management in these structures. The extent of device self-heating is shown to be strongly dependent on both device biasing configuration as well as geometry.

Monte Carlo based microscopic description of electron transport in GaAs/Al0.45Ga0.55As quantum-cascade laser structure

Results of multiparticle Monte Carlo simulations of midinfrared quantum cascade lasers structure initially fabricated by Page et al. are presented. The main aim of this paper is to discuss in details how electric current flows through the structure and which subbands are involved in this process. Monte Carlo method allows to predict the electron population inversion between the lasing levels and gives microscopic insight into processes leading to such behavior. Importance of a subband belonging to the laser injector region, with energy slightly below the upper lasing level, is demonstrated. The electron–electron Coulomb interactions influence the shapes of electron distribution functions; the values of average electron energies and effective subbands’ temperatures are calculated.

Monte Carlo study of electron transport in monolayer silicene

Electron mobility and diffusion coefficients in monolayer silicene are calculated by Monte Carlo simulations using simplified band structure with linear energy bands. Results demonstrate reasonable agreement with the full-band Monte Carlo method in low applied electric field conditions. Negative differential resistivity is observed and an explanation of the origin of this effect is proposed. Electron mobility and diffusion coefficients are studied in low applied electric field conditions. We demonstrate that a comparison of these parameter values can provide a good check that the calculation is correct. Low-field mobility in silicene exhibits temperature dependence for nondegenerate electron gas conditions and for higher electron concentrations, when degenerate conditions are imposed. It is demonstrated that to explain the relation between mobility and temperature in nondegenerate electron gas the linearity of the band structure has to be taken into account. It is also found that electron–electron scattering only slightly modifies low-field electron mobility in degenerate electron gas conditions.

Study of the high-frequency performance of III-As nanojunctions using a three-dimensional ensemble Monte Carlo model

We apply a well-calibrated three-dimensional Monte Carlo simulator using finite-element meshing to study the intrinsic high-frequency (HF) behaviour of three-terminal nanojunctions based on InGaAs/InAlAs heterostructures. To obtain a reliable prediction of device performance, we use a realistic model for surface charge effects at high-frequency conditions. In this work, we perform an analysis of the dynamics of electron transport in the devices and present a prediction of their intrinsic HF performance. The results demonstrate the suitability of these nanostructures for application in the terahertz regime, and illustrate the influence of surface charge effects in this frequency range.

Modified Monte Carlo method for study of electron transport in degenerate electron gas in the presence of electron–electron interactions, application to graphene

Standard computational methods used to take account of the Pauli Exclusion Principle into Monte Carlo (MC) simulations of electron transport in semiconductors may give unphysical results in low field regime, where obtained electron distribution function takes values exceeding unity. Modified algorithms were already proposed and allow to correctly account for electron scattering on phonons or impurities. Present paper extends this approach and proposes improved simulation scheme allowing including Pauli exclusion principle for electronelectron (ee) scattering into MC simulations. Simulations with significantly reduced computational cost recreate correct values of the electron distribution function. Proposed algorithm is applied to study transport properties of degenerate electrons in graphene with ee interactions. This required adapting the treatment of ee scattering in the case of linear band dispersion relation. Hence, this part of the simulation algorithm is described in details.

Delay time calculation for dual-wavelength quantum cascade lasers

In this paper, we calculate the turn-on delay (tth) and buildup (Δt) times of a midinfrared quantum cascade laser operating simultaneously on two laser lines having a common upper level. The approach is based on the four-level rate equations model describing the variation of the electron number in the states and the photon number present within the cavity. We obtain simple analytical formulae for the turn-on delay and buildup times that determine the delay times and numerically apply our results to both the single and bimode states of a quantum cascade laser, in addition the effects of current injection on tth and Δt are explored.

Self-consistent electrothermal Monte Carlo modeling of nanowire MISFETs

In this paper, we present a newly developed finite-element-based three-dimensional electrothermal Monte Carlo simulator, suitable for the study of a wide variety of nanodevices including nanowire-based structures. By relying on phonon statistics, electrothermal effects are accounted for through the coupling of an ensemble Monte Carlo trajectory simulation with the solution of the heat diffusion equation. The simulation model, which is suitably calibrated with experimental data, is employed to investigate carrier transport, and heat generation and transfer in metal-insulator field-effect transistors (MISFETs) based on a single InAs nanowire channel.

Microscopic simulation of electron transport and self-heating effects in InAs Nanowire MISFETs

We use a newly developed three-dimensional electrothermal Monte Carlo simulator, using finite-element meshing, to study metal-insulator field-effect transistors (MISFETs) based on a single InAs Nanowire. The model involves the coupling of an ensemble Monte Carlo simulation with the solution of the heat diffusion equation, and is carefully calibrated with data from experimental work on these devices. The simulator is applied to investigate electron transport and demonstrate the importance of self-heating in such devices characterized by high current densities.