Binding energy of indirect excitons in asymmetric double quantum wells

A new method of creating indirect excitons in asymmetric double quantum wells, based on mass filtering, is introduced in this paper. It is shown that different tunneling times of electrons and holes from the narrow well to the wide one in connection with fine tuning of the carrier density by a small barrier photoexcitation allow the creation of an electrically neutral system of indirect excitons. Resonant microwave absorption is investigated in such a double-layer system which detects both size-dependent plasma resonances for the case of a charged electron-hole system and size-independent indirect exciton 1S-2S transitions in the case of a neutral system. The exciton transition energy is measured as a function of the layer separation, and a contradiction with theoretical predictions is established which indicates a strong dielectric screening of excitonic states due to overlap of their wavefunctions.