DIRECT MEASUREMENT OF EXCITON DIFFUSION IN QUANTUM-WELLS

We have measured the diffusion of excitons in GaAs quantum wells by us ing spatial and time-resolved photoluminescence (PL) spectroscopy at l iquid helium temperature. A displacement of the detected region (empty set 1.5 mu m) with respect to the laser spot allows us to monitor the lateral change of the PL time-dependence. With increasing displacemen t the maximum of the PL-intensity shifts systematically to later times . For a theoretical description an in-plane diffusion model is applied , with the diffusion constant D as the only fit parameter. We obtain a continuous increase of D from 15 cm(2) s(-1) to 80 cm(2) s(-1) for di splacements from 0 to 4.2 mu m. A measurement with only spatial resolu tion leads to a diffusion constant of 20 cm(2) s(-1).