Raman, Brillouin, Infrared and Modulation Spectroscopy of Collective and Localized Excitations in Crystals and their Heterostructures

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This proposal focusses on theoretical and experimental investigations on tetrahedrally co-ordinated II-VI semiconductors (including diluted magnetic semiconductors: DMS's) and their heterostructures as well as II-VI/III-V and III-V heterostructures, the heterostructures being grown by molecular beam epitaxy (MBE). The investigations will address fundamental issues such as the nature of the ground and excited states of the transition metal (magnetic) ions in the tetrahedral environment of the II-VI semiconductors; the spin-spin exchange interaction between the magnetic ions and the band electrons; long range order; and electronic states of donors and acceptors. The new physics associated with MBE-grown quantum well structures will be studied in the context of the reduced dimensionality, interfaces, band off-sets and elastic strains. Raman, Brillouin, infrared and modulation spectroscopy will be exploited to discover and delineate the collective and localized excitations, with and without external perturbation (stress and magnetic). Theoretical investigations in parallel will provide motivation and framework for special lines of investigation and analysis of experimental results.