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Studies of optical and electrical properties of semicondutor heterostructures


The fundamental theme of this project is the characterization of the optical and electrical properties of artificially grown semiconductor materials, with a special emphasis given to the low dimensional semiconductor structures (superlattices, quantum well and quantum dots). For this, four techniques already established in the Semiconductors Laboratory of Department of Physics, UFSCar, will be applied: the Raman spectroscopy (macro and micro), Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence and Capacitance spectroscopy. The proposed characterizations are expected, by on side, to provide important information to the laboratories involved in the fabrication of these materials - that certainly will contribute do improve the qualities of the structures looking forward to the technological applications. By de other side, the proposed analysis will undoubtedly provide contributions to better understand the physics of the studied systems. Among the systems to be analyzed, are: semiconductor non doped and doped (GaAS)n(A1As)m superlattices (both the spatially limited and the intentionally disordered superlattices will be studied); the InAs quantum dots (either doped or non doped ones); the resonant tunneling heterostructures based on the HI-V systems (GaAs/GaAlAs, GaAs/InGaAs/A1As, GaAs/AlAs and InGaAs/InGaAsP); the doped AlxGa1-xAs alloys and milled semiconductor materials (Si, GaAs, InSb, InAs, GaSb, GaP). Concerning the Raman spectroscopy (normal and resonant), and the FTIR spectroscopy, careful analysis of the spectra with respect to their frequencies, relative intensities, width and line shapes, both of the phonons and the coupled plasmon-LO phonon modes (in the case of the doped samples), are expected to provide important information such as: localization effect of carriers, dispersions (in the case of plasmons) in spatially limited superlattices, the effects of heat treatments on the quantum dots and superlattices, the anisotropy of the superlattice optical phonons (and the structural quality of the superlattices), effects of solid solution on the vibration spectra, etc. The studies of both the photoluminescence and the excitation spectroscopy of the luminescence of the resonant tunneling heterostructures should allow to analyze the accumulation of charges in the wells, the tunneling via F - X, the effect of interface roughness, involving the formation of islands in the quantum well, and of the strain in the tunneling process, the formation of negatively carried excitons, (X-) in the quantum well, and finally, the study of the spin polarization.The electrical characterization techniques, and particularly the Capacitance spectroscopy, are going to be used to determine the spatial localization and the energy levels in the samples, with special emphasis in the GaAs/AlAs superlattices (with and without intentional period fluctuations), quantum dots superlattices and AlGaAs alloys. The proposed studies will, whenever it is reasonable, relevant and viable, include at least two of the available characterization techniques, a behavior already adopted in our laboratory. (AU)

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