On the relaxation time hierarchy in dissipative systems: An example from semiconductor physics

We consider the question of the contraction of the macroscopic nonequilibrium thermodynamic description of dissipative dynamic systems. As argumented by Bogoliubov, this process is associated to the determination of a spectrum (hierarchy) of relaxation times. We have used studies of the irreversible evolution of highly photoexcited plasmas in polar semiconductors to provide a way to exemplify and test the existence of such a spectrum of characteristic times. It is shown that, in fact, several kinetic stages can be characterized, each accompanied by a successive contraction in the description of the macroscopic state of the system. A proper choice, depending on the experimental conditions, leads to good agreement with observational data.