Two-dimensional Monte Carlo particle-based simulations of ultra-small MOSFETs

This thesis explains an Ensemble Monte Carlo code (EMC) and a two-dimensional Monte Carlo Poisson Solver (MCPS) that were developed as part of this Master's Thesis research. The EMC code was used for bulk silicon description, and the MCPS solver was used for modeling ultra-small n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). The commercially available Silvaco's device simulator was also used to model 2 μm and 50 nm n-channel MOSFETs.; Simulation results are presented for the time evolution of the electron drift velocity and energy in bulk silicon materials for various electric fields. Ultra-small MOSFETs were thoroughly studied using the MCPS. The simulation results for 50 nm gate-length n-channel MOSFET device include potential energy, electric field, electron and charge density profiles inside the device structure for both equilibrium and non-equilibrium conditions. The output and the transfer characteristics of this device structure, obtained with the MCPS, are also presented and discussed. The simulation results suggest that doping in the bulk in excess of 1018 cm−3 is needed to prevent the punch-through effect. Also, doping density underneath the gate that is lower than 5 × 1017 cm −3 is needed to have acceptable threshold voltages. The MCPS was also used to investigate the performance enhancement of focused-ion-beam metal-oxide-semiconductor (FIBMOS) devices with respect to standard MOSFET device structures.; MOSFET devices with gate length of 50 nm and 2 μm were also investigated with Silvaco. These results have been very helpful in guiding the experimental efforts within the Nanostructures Research Group at Arizona State University.