Physics and simulation of quasi-ballistic transport in nanoscale transistors

The formidable progress in microelectronics in the last decade has pushed the channel length of MOSFETs into decanano scale and the speed of BJTs into hundreds of gigahertz. This progress imposes new challenges on device simulation as the essential physics of carrier transport departs that of conventional approaches because the effects of quasi-ballistic transport and quantum phenomena on device and circuit performance are becoming more important. Although a full quantum approach such as nonequilibrium Green's function method naturally accommodates the two issues and a semiclassical first principle such as Monte Carlo simulation resolves at least the issue of quasi-ballistic transport, their heavy computational prevents them from playing a major role in exploring a wide range of device design options in practice. Hence, it is of great interest to develop a new macroscopic approach for the simulation of nanoscale devices operating near the ballistic limit. This motivates the present study to explore the feasibility of such an attempt. Therefore, the purpose of this study is to understand essential physics of quasi-ballistic transport and its implications to nanoscale device simulation based on macroscopic transport models. The study is composed of three parts; one is to understand the essential physics of quasi-ballistic transport in a device context, another is to identify the limitations of commonly used transport models in assessing nanoscale devices, and the other is to explore new macroscopic transport models valid from the diffusive to the ballistic limit.