Experimental evidence of the role of acoustic plasmons in carrier relaxation dynamics in bulk semiconductors

Summary form only given. The relaxation of a nonequilibrium population in the presence of equilibrium carriers is a situation frequently encountered in devices. It is also interesting from the fundamental point of view since theoretical work has predicted the existence of weakly damped acoustic plasmons under nonequilibrium situations and their importance in accelerating the relaxation as well as a drastic dependence on the temperature of thermalized electrons existing in addition to a nonequilibrium electron-hole plasma. However, no experimental investigation of acoustic-plasmon effects in nonequilibrium plasmas has been performed up to now. We here present the first experimental evidence for the role of acoustic plasmons by measuring the relaxation in the presence of hot or cold equilibrium carriers injected by a prepump in a 0.65-/spl mu/m GaAs layer. We use a nondegenerate pump-probe configuration that allows to follow selectively the thermalization of the nonequilibrium electron distribution.