Showing papers by "Áurea R. Vasconcellos published in 1991"

Collective Behaviour of Photoinjected Plasma in Semiconductors

Abstract: The spectrum of elementary excitations in the nonequilibrium state of a semiconductor under high levels of continuous photoexcitation is studied. Resorting to a quantum transport theory based on the nonequilibrium statistical operator method, the dynamic dielectric response function of the carrier system in the far-from-equilibrium steady state is derived, to calculate the Raman scattering spectrum and from it to analyze the spectrum of elementary excitations. Besides the expected bands due to quasi-particle and collective plasma excitations, the presence is demonstrated of two additional bands associated to low energy excitations and with a linear dispersion relation, and hence termed acoustic plasma modes. The analysis of these two bands points to an interpretation of them as due to the collective motion of the electrons (the ones higher in energy) and of the holes (the ones lower in energy) interacting through the screened Coulomb interaction. At low temperature their lifetimes are mainly determined by dissipative effects mediated by the interaction of the carriers with the radiation recombination field.