| The main theme of this thesis is a series of studies of physics-based numerical modelling issues with special emphasis on organic field effect transistors (OFETs). Organic semiconductors are gaining attention as candidate materials for a low-cost technology of fabricating large area integrated circuits. However, the device geometry, operation and material properties of OFETs are unusual compared with field effect transistors based on inorganic semiconductor materials, such as Si and GaAs. Therefore, the conventional knowledge developed for these devices is not directly applicable to OFETs. Several different approaches for the task of formulating physical models for OFETs are explored in this thesis. We use a finite difference method with Scharfetter-Gummel discretization to obtain the solution to the nonlinear Poisson equation and the drift-diffusion equation that govern the operation of field effect transistors to carry out a series of studies on the issues that are unique to OFETs, i.e. [a] channel formation due to injected charge carriers, [b] contact resistances associated with non-ohmic injecting source and drain contacts. Furthermore, a compact analytic model is derived to help extract technologically important parameters, such as the field effect mobility, without the specific need to consider the contact resistances.; Another topic studied in the framework of this thesis is a rigorous examination of solving the nonlinear heat dissipation problem for hetero-structure power transistors. A self-consistent boundary condition scheme is proposed and implemented. The results demonstrate the validity of using the Kirchhoff transformation as an approximation in a non-self consistent calculation. |
