Impact of strong quantum confinement on the performance of a highly asymmetric device structure: Monte Carlo particle-based simulation of a focused-ion-beam MOSFET

A highly asymmetric 250 nm n-channel MOSFET, with a 70-nm p(+)-implant placed at the source end of the channel (achievable by focused-ion-beam (FIB) implantation, so the device is named FIBMOS), has been simulated using a two-dimensional (2-D) coupled Monte Carlo-Poisson solver, in which quantum confinement effects have been taken into account by incorporating an effective potential scheme into the particle simulator. Although the device is a long-channel one, its performance is dictated by the highly doped p(+)-implant at the source end of the channel, and it is crucial to properly account for the quantum-confinement effects in transport, especially at the implant/oxide interface. We show that parameters such as threshold voltage and device transconductance are extremely sensitive to the proper treatment of quantization effects. On the other hand, the built-in electric field, due to the pronounced asymmetry caused by the presence of the p(+)-implant, drastically influences the carrier transport, and consequently, the device output characteristics, in particular the magnitude of the velocity overshoot effect and the low-field electron mobility.