Usage of strained silicon can improve performance of both NMOS and PMOS devices. This design option is already employed in the present 90nm technology node. Physical models and parameter values of TCAD tools have to be carefully upgraded to cover the properties of the strained Si/SiGe material system. A main goal of this project is the development of mobility models for strained silicon. A physically-based bulk mobility model has been developed, which takes into account the strain-induced valley splitting and the resulting valley repopulation. The model is based on ideas developed by Manku and Nathan. A term accounting for inter-valley scattering has been added. This effect has been found important to improve agreement with experimental data and bulk Monte Carlo (MC) data produced using VMC. Quantitative analysis of hole transport in strained semiconductors requires a numerical representation of the band structure. For this purpose, a full-band MC kernel is currently being developed. Momentum space is discretized using tetrahedrons, which allow effective interpolation and integration of the equations of motion. The band structure is calculated by a solver implementing the nonlocal, empirical pseudopotential method.

Development of an MC simulator for the transport in channels has continued. The simulator reads in the sub-band energies and overlap integrals computed by a self-consistent Schroedinger-Poisson solver. Using adjusted surface roughness and phonon scattering parameters the simulator reproduces the universal electron mobility curve for unstrained silicon and gives reliable predictions for strained silicon channels. The Lombardi model is used as a starting point for the development of an analytical, strain-dependent surface mobility model.

A new project on the modeling of silicon FETs near the scaling limit has been commenced. The recently developed MC module for the Wigner-Boltzmann equation will be applied. Goals are the inclusion of size quantization effects and a more realistic band structure in the transport model. Recently, the multi-valley band structure of silicon has been implemented in the Wigner MC module, which has originally been benchmarked on GaAs-based resonant tunneling diodes.

Various architectures of carbon nanotube (CNT) FETs have been studied using Minimos-NT. Assuming ballistic transport, a Schroedinger-Poisson solver is used to analyze the Schottky barriers. The current is then calculated using the Landauer-Buettiker formula. The charge on the tube can now be taken into account self-consistently. To optimize the off-state characteristics of the CNT-FET, a dual-gate structure has been proposed. The second gate effectively suppresses hole tunneling at the drain contact.