Excitonic binding in coupled quantum wells

We study excitonic states in the presence of applied electric field in 8-nm GaAs coupled quantum wells (QW's) separated by a 4-nm Al0.33Ga0.67As barrier and in 6-nm In0.1Ga0.9As coupled QW's separated by a 4-nm GaAs barrier in which effects attributed to macroscopically ordered excitonic states have been recently reported. We discuss the differences in the nature of the states and in the origin of confinement which determines the change of excitonic properties with increase in the applied electric field in both structures. We have found that the indirect exciton binding energy for the field amplitude used in the experiment with InGaAs QW's is around 3.5 meV, much less than the previously reported 10 meV value. This suggests that the optically induced ring structure, reported to persist to near 100 K, might not be caused by collective excitonic transport.