CARRIER SCATTERING AND EXCITONIC EFFECTS ON ELECTRON-HOLE-PAIR DIFFUSION IN NONDOPED AND P-TYPE-MODULATION-DOPED GAAS ALXGA1-XAS QUANTUM-WELL STRUCTURES

We have performed lateral-diffusion measurements of photoexcited elect ron-hole pairs at various excitation densities for nondoped and p-type -modulation-doped GaAs/Al0.3Ga0.7As multiple-quantum-well structures a t 77 K, using an all-optical time-of-flight technique with a single-mo de optical-fiber probe. Systematic measurements at various electron an d hole densities revealed remarkable deviation from the conventional a mbipolar diffusion, indicating the important contribution of carrier-c arrier scattering and excitonic effects to the diffusion.