A structure grown by metalorganic chemical vapor deposition (MOCVD), consisting of ten periods of alternating layers of n- and p-doped GaAs 130-nm thick with a doping concentration of 2 × 1017, was studied. The nonlinear transmission spectrum as a function of intensity as well as the intensity-dependent carrier buildup and decay lifetimes were measured directly using a pump-probe technique. The differential transmission spectrum (ΔT/T) at various pump intensities and the buildup time required to obtain the maximum modulation for a given intensity are shown and discussed. The intensity-dependent decay dynamics was measured by delaying the probe relative to the falling edge of the pump pulse. On a log-log scale the decay of the maximum modulation is linear, indicating a decay time that increases exponentially with decreasing carrier density. Both the buildup and decay dynamics can be effectively modeled with a rate equation whose carrier decay time depends exponentially on carrier density.