3.1 Partitioning of the Simulation Domain

In MINIMOS-NT the simulation domain is partitioned into nonoverlapping regions which are called segments. This partitioning is done with respect to the material class, e.g., contacts, insulators, and semiconductors. When the simulation domain is properly split into segments, there are no abrupt changes of the material parameters within the segments. Abrupt variations of the material parameters should only occur at the interface of two adjoining segments.

Partitioning the simulation domain into segments allows the use of different models for each of the segments. For example the set of differential equations used for modeling the physical properties can be chosen individually for each segment. This allows to solve the hydrodynamic equations in regions where the carrier temperature differs considerably from the lattice temperature and influences the simulation result. In the remaining simulation domain, where the effects of carrier heating can be neglected the simpler drift-diffusion model can be used. This approach reduces the number of unknowns and improves convergence.

Not only the set of differential equations used for simulation can be chosen individually for each segment. In a similar way different physical models for all kind of quantities, e.g., carrier mobility, effective carrier mass, band edge energies, band gap narrowing, and recombination mechanisms, can be selected for each segment.

Fig. 3.1 shows schematically the partitioning of the simulation domain of a simplified high electron mobility transistor (HEMT) into segments with respect to material classes and properties. The semiconductor region of the device is partitioned into three segments. Two segments for the AlGaAs regions and one for the InGaAs channel region. With this separation into different segments it is possible to specify different carrier mobility models and saturation velocities for each region. Each of the Al contacts is modeled as a separate segment and the contact type can be specified separately. For the source and drain contacts where the doping concentration is very high in the adjoining semiconductor a model for an Ohmic contact is used. At the gate contact the doping concentration is low and therefore a Schottky contact model is chosen.

Figure 3.1: Material types and partitioning of the simulation domain into segments for a simplified HEMT.