ABSTRACT
This discusses electrical conduction and related phenomena in semiconductors. In equilibrium, the electron and hole densities can be expressed in terms of the Fermi level, but in nonequilibrium, we need to consider separate quasi Fermi levels for electrons and holes, respectively. These can be understood as nonequilibrium carrier densities converted into quantities that can be drawn on an energy band diagram. The conduction current density is proportional to the carrier density and the gradient of the quasi Fermi level, with the constant of proportionality being the mobility. The conduction current consists of drift current that flows due to external forces acting on carriers, and diffusion current that flows due to the density gradient of carriers. The minority carrier lifetime is the time constant associated with the generation-recombination processes. From an energy band diagram with quasi Fermi levels for electrons and holes, one can read various information about the device. The basic equations for semiconductor devices consist of the continuity equations for charge and current and the Poisson equation for the electrostatic field. Important time constants related to carrier dynamics are the minority carrier lifetime and the dielectric relaxation time.
