Wave-function mapping in multiple quantum wells using diluted magnetic semiconductors

We have shown that in symmetric multiple quantum wells (QW’s), wave functions of the lowest multiplet of states have rather surprising distributions, where some states are localized only in certain wells, and are totally absent in other wells. To demonstrate this experimentally, we have used magnetoabsorption measurements to map out the distribution of wave functions in multiple-quantum-well structures in which some layers consist of diluted magnetic semiconductors (DMS’s). For this purpose we fabricated triple- and quintuple-QW systems consisting of ${\mathrm{Zn}}_{1-x-y}{\mathrm{Cd}}_x{\mathrm{Mn}}_y\mathrm{Se}$ (DMS) and ${\mathrm{Zn}}_{1-x}{\mathrm{Cd}}_x\mathrm{Se}$ (non-DMS) wells, separated by ZnSe (i.e., nonmagnetic) barriers. Transitions involving the lowest multiplet of states (i.e., the ground state split by interwell interactions) were clearly observed and well resolved at zero magnetic field. The wave-function behavior in multiple quantum wells of equal depth was investigated by observing the Zeeman splitting of the optical transitions at 30 K, where the Zeeman splitting of DMS band edges is small compared to the band offset, so that the wells remain in near-resonant condition. This in turn results in strong (resonant) interactions between the wells. The experiments clearly demonstrated that for certain states there are wells in which the probability of finding an electron or a hole vanishes.