Raman, Brillouin, Infrared and Modulation Spectroscopy of Collective and Localized Excitations in Tetrahedrally Coordinated Semiconductors and their Heterostructures

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This research focuses on the vibrational, electronic, and magnetic excitations in tetrahedrally coordinated semiconductors. Both bulk and submicron heterostructures fabricated by molecular beam epitaxy and chemical vapor deposition will be investigated. II-VI and III-V semiconductors (bulk, epilayers, and quantum well structures) will be examined using Raman, Brillouin, modulated reflectivity, and photoluminescence and absorption spectroscopy. Magnetic ions introduced into II-VI compounds have resulted in a new class of materials called diluted magnetic semiconductors which possess striking magneto-optic effects. Further exploration of these systems will be undertaken with special emphasis on materials of low dimensionality. The vibrational spectra and electronic levels of donors and acceptors intentionally introduced into diamond and silicon carbide will also be studied. The thrust of the program is to provide a fundamental understanding of the physical properties of tetahedrally coordinated semiconductors whose optical characteristics form the basis of many optoelectronic applications. %%% The family of tetrahedrally coordinated semiconductors encompasses the well known group IV semiconductors such as C, Si, and Ge as well as the II-Vs (e.g., GaAs, InSb, etc.) and the II-VIs (e.g., CdTe, ZnTe, etc.) The electronic, vibrational, and magnetic excitations in these materials will be examined through spectroscopic investigations using a variety of techniques. The results of such spectral studies will yield important fundamental quantities related to their optical properties and are expected to form the basis of many optoelectronic devices. In particular, magnetic ions introduced into the II-VIs generate striking magneto- optic effects which have potential applications as magnetic isolators and optical sensors. These novel advanced material systems are accessible to both experimental and theoretical studies, thanks to the ingenious techniques increasingly exploited in the growth of new semiconductors in the bulk as well as with submicron dimensions. The work will be done in collaboration with scientists and technologists at several industrial research laboratories who will supply many of the materials. In addition, the program benefits from an active collaboration with the Argonne National Laboratory.