Variation of inter-well coupling in magnetically tunable multiple quantum wells

We have investigated the problem of inter-well coupling in multiple quantum well (OW) systems using magnetooptical experiments. A series of multi-OW structures consisting of II-VI-based diluted magnetic semiconductor (DMS) and non-magnetic semiconductor wells were used for this purpose. In one study, we used a double quantum well structure consisting of non-magnetic quantum wells (Zn_1-yCd_ySe) separated by DMS barriers (Zn_1-xMn_xSe). The dependence of coupling strength on inter-well barrier height was studied by examining the energy splitting of the lowest multiplet of states. We have also investigated inter-well coupling in triple quantum well structures. For this purpose we designed symmetric triple quantum wells consisting of DMS (Zn_1-x-yCd_yMn_xSe) and non-DMS (Zn_1-yCd_ySe) semiconductor wells, separated by non-magnetic ZnSe barriers. Transitions involving the lowest multiplet of states were clearly observed and well resolved at zero magnetic field. The strongest interaction between the states in such triple quantum wells occurs when the wells are identical (i.e., when they are in resonant condition). As soon as the depths of the wells become unequal (achieved by Zeeman splitting in the presence of an external magnetic field), the coupling between the wells is dramatically reduced.