Electric-field effects on exciton lifetimes in symmetric coupled GaAs/Al0.3Ga0.7As double quantum wells

We have studied the effects of coupling on the lifetime of spatially indirect excitons in (50-Å GaAs)/${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As symmetric double quantum wells. The coupling was controlled by varying the barrier thickness between 25 and 60 Å and by application of an electric field. Lifetime enhancements of up to 3 orders of magnitude relative to the lifetimes of spatially direct excitons were observed. At a given electric field the lifetime enhancement was larger the wider the barrier, due to the smaller electron-hole wave-function overlap, in good agreement with theory. We have also observed nonresonant hole tunneling and estiimated the tunneling time, which was of the order of 300 ps in a 40-Å-barrier sample.