Abstract
We report the use of a time-resolved transient-grating technique to study the in-plane ambipolar diffusion coefficient and interwell tunnelling probability for excitons in a number of multiple quantum well samples. Our specimens were selected with barrier thicknesses ranging from 14 to 141 AA thus giving complete coverage of the transition from isolated quantum well to superlattice behaviour. Two types of MBE growth conditions were used giving rise to samples with low or high surface defect density. The surface defect density had a strong effect on the in-plane mobility but not the tunnelling probability. The samples show surprisingly strong interwell coupling even with the thickest barrier, which we attribute to defect assisted tunnelling.
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