9722625 McCombe This is a new project in which optically Detected Resonance (ODR) spectroscopy, which combines the sensitivity of near IR/visible photon detection with far IR excitation, will be used to investigate basic issues related to many-body interactions of electrons and holes in low-dimensional semiconductor systems. Intraband electronic excitations of very low densities of photoexcited carriers and carrier complexes can be investigated in this way. Specific projects include: internal states of neutral and charged excitons in high magnetic fields; effects of excess electrons and holes on excitonic states and the metal- insulator transition; many body effects in the integer and fractional quantum hall effect regimes through the influence of donor impurities on the far IR excitations; and ODR echanisms. This research will yield unique information about excitons, effects of excess carriers on their internal states, mechanisms of energy ransfer to the ground state recombination paths, and insight into the any-body ground states of electrons at low temperatures and high magnetic fields. %%% This is a new project in which a novel technique that combines sensitive near infrared/visible detection with resonant absorption in the far infrared region of the spectrum, Optically Detected Resonance (ODR) spectroscopy, will be used to investigate the allowed energy states of charge carriers in small (tens of nanometers) man-made semiconductor structures. The unique electronic and optical properties of these structures are determined by quantum mechanics and the interactions of the charge carriers, electrons or holes. This research will yield unique information about and improved understanding of the energy states of electrons and holes bound together (the so-called exciton), the effects of excess free electrons and holes on these states, and how e nergy absorbed in exciting the electron-hole system is transferred back to the lowest energy states and subsequently leads to recombination and light emission. This work will also provide insight into the interesting many-electron states that exist at low temperature and in high magnetic field, the Quantum Hall and Fractional Quantum Hall states. ***
