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Please use this identifier to cite or link to this item: http://hdl.handle.net/2005/665

Title: Effects Of Spin Polarization And Spatial Confinement On Optical Properties Of Bulk Semiconductors And Doped Quantum Wells
Authors: Joshua, Arjun
Advisors: Venkataraman, V
Keywords: Spin Polarization
Doped Quantum Well
Spin-Polarized Semiconductors
Quantum Wells - Electro-Optical Properties
Spin-Polarized Semiconductors - Optical Nonlinearities
Kerr Rotation
Allan Variance
Submitted Date: Feb-2009
Series/Report no.: G22939
Abstract: We correlated experimental results with theoretical estimations of the dielectric function ε(ω) in two contexts: the effect of an electric field in quantum wells and that of the spin polarization of an interacting electron-hole plasma in bulk semiconductors. In the first part, we recorded photoreflectance spectra from Ge/GeSi quantum wells of different widths but having comparable builtin electric fields caused by doping. The reason why the spectra differed in overall shape was difficult to understand by conventional methods, for example, by calculating the allowed transition energies or by fitting the data with lineshape functions at each transition energy. Instead, we computed the photoreflectance spectra from first-principles by using the confined electron and hole wavefunctions. This method showed that the spectra differ in overall shape because of the experimentally hitherto unobserved trend in quantum well electro-optical properties, from the quantum confined Franz-Keldysh effect to the bulk Franz-Keldysh effect, as the well width is increased. The second part develops a threeband microscopic theory for the optical properties due to spin-polarized carriers in quasiequilibrium. We show that calculations based on this theory reproduce all the trends observed in a recent circularly polarized pump-probe experiment reported in the literature. To make the computation less intensive, we proposed a simplified, two-band version of this theory which captured the main experimental features. Besides, we constructed a cw diode laser-based pump-probe setup for our own optical studies of spin-polarized carriers by Kerr rotation. We achieved a sensitivity of detection of Kerr rotation of 3 x 10¯ 8 rad, corresponding to an order of magnitude improvement over the best reports in the literature. The efficacy of our setup allowed for the demonstration of a pumpinduced spin polarization in bulk GaAs, under the unfavorable conditions of steady-state and room temperature.
URI: http://etd.iisc.ernet.in/handle/2005/665
Appears in Collections:Physics (physics)

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