TRANSIENT ELLIPSOMETRIC SURFACE PHOTOREFLECTANCE APPLIED TO GAAS

We apply a time-resolved reflection ellipsometric technique to study t he dynamic properties of the surface dielectric index of GaAs after op tical excitation. The technique allows the separation of the refractiv e and absorptive components of the dielectric index change and account s for possible anisotropic effects. The carriers optically injected at the surface create electric field perturbations of approximately 7 kV /cm for an average carrier density of approximately 10(18) cm-3 over a depth of approximately 0.25 mum. The measured absorptive component ch ange is shown to be qualitatively different from that typically measur ed via thin-film transmission and can be attributed to the Franz-Keldy sh effect.