We compare the numerical results for electron direct tunneling currents for single gate oxides, ON- and ONO-structures. We demonstrate that stacked dielectrics can keep the tunneling currents a few orders of magnitude lower than electrostatically equivalent single oxides. We also discuss the impact of gate material and of the modeling of electron transport in silicon.

RF noise in quarter-micron nMOSFETs is analysed on the device level based on Shockley's impedance field method. The impact of different transport models and physical parameters is discussed in detail. Well-calibrated drift-diffusion and energy-balance models give very similar results for noise current spectral densities and noise figures. We show by numerical simulations with the general-purpose device simulator DESSIS_ISE that the hot-electron effect on RF noise is unimportant under normal operating conditions and that thermal substrate noise is dominant below 0.5 GHz. The contribution of energy-current fluctuations to the terminal noise is found to be negligible. Application of noise sources generated in bulk full-band Monte Carlo simulations changes the noise figures considerably, which underlines the importance of proper noise source models for far-from-equilibrium conditions.

The density gradient (DG) model is tested for its ability to describe tunneling currents through thin insulating barriers. Simulations of single barriers (MOS diodes, MOSFETs) and double barriers (RTDs) show the limitations of the DG model. For comparison, direct tunneling currents are calculated with the Schrodinger-Bardeen method and used as benchmark. The negative differential resistance (NDR) observed in simulating tunneling currents with the DG model turns out to be an artifact related to large density differences in the semiconductor regions. Such spurious NDR occurs both for single and double barriers and vanishes, if all semiconductor regions are equally doped.

TCAD is gaining acceptance in the heterostructure industry. This article discusses the specific challenges a device simulator must manage to be a useful tool in designing and optimizing modern heterostructure devices. Example simulation results are given for HEMTs and HBTs, illustrating the complex physical processes in heterostructure devices, such as nonlocal effects in carrier transport, lattice self-heating, hot-electron effects, traps, electron tunneling, and quantum transport.

A TCAD implementation of a quantum-mechanical mobility model in the commercial device simulator DESSIS_ISE is presented. The model makes use of an integrated 1D Schrodinger-Poisson solver. Effective mobilities µeff and transfer characteristics are calculated for DGSOI MOSFETs with a wide range of silicon film thickness tSi and buried-oxide thickness tbox. It is shown that the volume-inversion related enhancement of µeff for tSi 10 nm is bound to symmetrical DGSOIs, whereas SIMOX based devices with thick buried oxides limit µeff to the bulk value. The still immature technology makes a conclusive comparison with experimental data impossible.