Energy Transport of Strongly Localized Excitons in 2D Limit: Monolayers of Te Isoelectronic Traps in ZnSe

It is now well established that Te is a strong isoelectronic center for excitons in II-VI compound semiconductors such as ZnSe [1],[2], and ZnS [3], Deeply bound states (>100 meV) exist due to the attractive short range potential by Te for holes. Furthermore, it has been argued [2] that the process involves strong local lattice relaxation in a dynamical sense, i.e. that photoexcited holes are subject to self-trapping while the electron component of the exciton simply Coulomb orbits the ’Frenkel-like’ hole [4]. The use of such isoelectronic centers may be especially useful in developing light emitters in the blue-green region of the spectrum. Fundamentally, introducing the centers by ’delta-doping’ can provide an unusual opportunity to study 2-dimensional energy transport of carriers under conditions of strong localization and coupling to the lattice; i.e. a lower dimensional ’polaron’ problem. We have performed optical experiments, including direct imaging of trapped exciton population gratings, to obtain first results in ZnSe-based superlattices and quantum wells where incorporation of one or two monolayers of ZnTe by atomic layer epitaxy provides a planar distribution of Te isoelectronic centers.