2.3 The Thermodynamic Model

In [44] Wachutka regards the semiconductor material as a composite thermodynamic system which comprises the subsystems of electrons, holes, and host lattice. These three subsystems are affected by the action of external fields and interact with each other according to certain rules. For example, particle flow between holes and electrons is governed by recombination processes; or lattice scattering enables energy transfer between the carriers and the lattice.

The whole semiconductor can be uniquely characterized by a set of state variables which are position and time dependent. In semiconductor modeling these variables are the quasi Fermi levels, the carrier temperature, and the lattice temperature. The quasi Fermi level is the sum of a chemical potential and an electric potential where the former is a local function of the carrier density and temperature, while the latter is determined via the Poisson equation [43].