Electron-LO-Phonon Quantum Kinetics in Wide-Gap II-VI Nanostructures with Strong Confinement

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This research investigates coherent coupling between excitons and longitudinal optical (LO)-phonons in II-VI quantum wells and quantum wires. Using ultrashort sub-20-femtosecond pulses, the coupling can be probed under conditions where the excitation time is shorter than the LO-phonon oscillation period. In addition to studying intrinsic properties and interference phenomena between strong Coulomb-interaction and large electron-LO-phonon coupling, the proposed wide-gap II-VI nanostructures with strong confinement also may allow unique tuning of the exciton binding energy above the LO-phonon energy. As a result novel quantum kinetic effects may be observed. The investigations will serve as crucial tests of extended quantum kinetic models and will contribute to an improved understanding and interpretation of the coherent electron-LO-phonon scattering in polar quasi-two and quasi-one dimensional nanostructures. Graduate students will gain experience in fundamental experimental techniques with cutting edge technology. This training will prepare them for a range of careers in academe, industry and government. %%%This work is directed at the study of coherent coupling between electronic excitations and lattice vibrations in wide-band-gap II-VI semiconductor nanostructures utilizing ultrashort femtosecond light pulses. In these experiments the optical excitation time is shorter than the lattice oscillation period so that at early times after excitation electron scattering processes can be treated as interference phenomena. The proposed research will uncover novel coherent effects and contribute to an improved understanding and interpretation of optically excited semiconductors at the interface between reversible and irreversible electron scattering. It will serve as a crucial test of extended theoretical models appropriate for these nanostructures. The experimental results will have a strong impact on theoretical research and will also have importance for information technologies. Students in this program receive rigorous training in ultrafast coherent optics and semiconductor physics, which prepares them for careers in academia or industry.***