Transport of nonequilibrium carriers in bipolar semiconductors

In this work we present results concerning the fundamental equations of charge-carrier transport in semiconductor structures. We discuss a correct modeling of the recombination terms that does not violate the charge conservation law. We obtained that under stationary conditions and equal generation rates of electrons and holes the recombination rates of both kinds of carriers must be matched. Under low excitation conditions (linear regime) the recombination rate can be expressed as a linear combination of the excess concentrations of electrons and holes, and only in very precise situations can a lifetime be defined. Explicit calculation of the charge variation was carried out within the framework of the band-to-band and Shockley-Read-Hall statistics. It is shown that the bulk space charge established on distances of the order of Debye’s length cannot influence the current-voltage characteristics of a device in a linear regime. It was also shown that metal-p-type semiconductor contacts are essentially different from those made on n-type semiconductors. The former should be considered as having a bipolar semiconductor structure and recombination cannot be neglected. The boundary conditions for the Poisson equation are presented.