The numerical simulation of semiconductor devices represents the most important means of characterizing and evaluating both fabrication processes and device designs. Based on a numerical model of the device structure, including wafer geometry and dopant distribution, the distribution of the electric potential, the current density, carrier densities, and the temperature are computed as a function of externally applied voltages. Most types of devices can be simulated; available simulation tools range from simulators specialized on certain device types [SSP80] to general semiconductor structure simulators [Fis94] [SKRS95] [Sim96]. The fact that the distribution of physical quantities in the semiconductor device is not observable in nature due to the limited resolution of measurement techniques holds even more for device operation. Simulation provides the only means for looking into the active device. For example, [RSS95] treats the analysis of the transient behavior of charged-coupled devices.