We calculate the intersubband mixing, brought about by the Coulomb interaction of electron-hole pairs in symmetric double quantum wells. On increasing the barrier thickness the exciton binding energy at first decreases because of the extra electron-hole separation. A further increase in the barrier thickness allows the symmetric and antisymmetric electron and hole subbands to mix, thereby localizing the exciton in one of the two wells. This leads to a rise in the exciton binding energy. We find a minimum in the binding energy as a function of barrier width. Additionally, a novel blue shift in the optical transition energy is predicted for small values of the applied electric field. The mechanism for this can also be related to intersubband mixing.

• Received 17 February 1989

DOI:https://doi.org/10.1103/PhysRevB.40.5515