Raman and Other Optical Studies of Semiconductors

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Raman scattering will be studied from folded acoustic phonons, confined optical phonons, and interface optical phonons in Gallium Arsenide/Aluminum Arsenide and Gallium Arsenide/Aluminum Gallium Arsenide superlattices under conditions where the excited laser light is in resonance with various transitions from valence subbands to conduction subbands. These measurements will be supplemented by photoluminescence, photoluminescence excitation, photoreflectance, and spectroscopic ellipsometry measurements. Goals include understanding details of electronic structure and electron-phonon coupling resulting from valence-band mixing, electron-hole exchange interaction, and three-dimensional behavior of superlattice wave functions. Equipment will be assembled for real-time spectroscopic ellipsometry measurements on a sample growing inside a molecular beam epitaxy machine. Real time comparisons will be made between ellipsometry results and reflection high energy electron diffraction measurements. Goals include improved understanding of epitaxial growth processes, incorporation of ellipsometric results into feedback control of the growth, and achievement of higher quality samples.