We report Raman studies of the Si–Si phonon band in Si1−xGex alloys, where the excitation is by visible and ultraviolet (351 nm) light. At a wavelength 351 nm, the optical penetration depth is extremely shallow (≈5 nm). By varying the excitation from 351 to 514 nm, the optical penetration depth spans from 5 to 300 nm. Two sets of samples were examined. Thin layers grown using molecular beam epitaxy were coherently strained to match the lattice constant of the silicon substrate. Thick layers grown using organo–metallic chemical vapor deposition were strain relaxed. For the thin, strained layers, visible excitation produces a spectrum, which is a superposition of the substrate and the epilayer phonon bands. Reducing the wavelength (and, consequently, penetration depth) allows us to isolate the epilayer spectrum. Phonon energies obtained using all excitation wavelengths agree. We conclude that Raman scattering from these alloys using 351 nm laser light gives us bulk alloy properties pertinent to the near-surface composition and strain. The epilayers show no evidence of compositional variance or strain relaxation near the surface.

Articles you may be interested inComparison of ultrathin Si O 2 ∕ Si ( 100 ) and Si O 2 ∕ Si ( 111 ) interfaces from soft x-ray photoelectron spectroscopy J.Photoemission and ab initio theoretical study of interface and film formation during epitaxial growth and annealing of praseodymium oxide on Si (001) We investigate microscopic properties of ultrathin oxynitride gate dielectrics using a combination of first principles electronic structure methods and the attenuated total reflection ͑ATR͒ infrared spectroscopy. We use a theoretical structural model based on the Si-SiO 2 interface. The quantum molecular dynamics simulations suggest that N accumulates at the interface. We have generated samples with the nitrogen concentrations from 1.69ϫ10 14 to 6.78ϫ10 14 cm Ϫ2 . The analysis of nitrogen containing cells indicates a significant structural improvement of the oxide layer and the strain reduction at the interface. We have performed a calculation of the vibrational density of states. The experimental infrared ATR data is in qualitative agreement with the calculation. The valence band offset is estimated with two different theoretical methods. Calculations reveal a close agreement between a reference energy level based method and a direct estimate based on the density of states analysis. For the highest nitrogen concentration considered we find a 0.3 eV increase of the valence band offset due to nitrogen at the interface. The leakage current is studied using the Landauer theory to model the conductance through the gate dielectric.

Few-layer epitaxial graphene grown on vicinal 6H-SiC studied by deep ultraviolet Raman spectroscopy Appl. Phys. Lett. 97, 033108 (2010); 10.1063/1.3466150Combinatorial ( Ba , Sr ) TiO 3 thin film growth: X-ray diffraction and Raman spectroscopy Stoichiometric and nonstoichiometric SrTiO 3 ͑STO͒ films less than 50 nm were grown by molecular beam epitaxy on Si substrates for characterization with UV-Raman spectroscopy. All the films grown have first order phonon Raman scattering as the crystal symmetry has been altered due to threading dislocations and local vicinal strain at defect sites. Strong phonon scattering and hardening of the phonon modes is seen in Ti-rich films while Sr-rich films have a decrease in the phonon scattering intensity when compared with stoichiometric thin films. Excess Ti leads to a high density of planar boundaries and different chemical phases lowering the overall crystal symmetry of STO. The Sr-rich sample compensates for excess Sr by forming SrO Ruddlesden-Popper layers in the perovskite structure.

Articles you may be interested inStructural and electrical properties of c-axis epitaxial homologous Sr m−3 Bi 4 Ti m O 3m+3 (m=3, 4, 5, and 6) thin films J. Appl. Phys. 94, 544 (2003); 10.1063/1.1579864 Microstructure and growth mode at early growth stage of laser-ablated epitaxial Pb(Zr 0.52 Ti 0.48 ) O 3 films on a SrTiO 3 substrate J. Appl. Phys. 89, 4497 (2001); 10.1063/1.1356426Effects of precursors and substrate materials on microstructure, dielectric properties, and step coverage of (Ba, Sr)TiO 3 films grown by metalorganic chemical vapor depositionWe have investigated the optoelectronic characteristics of bulk single-crystal SrTiO 3 (STO) and epitaxial STO on Si by photoluminescence and cathodoluminescence (CL) techniques. In particular, we have explored to what extent these techniques can offer information about crystal quality. We have complemented these observations with atomic force microscopy, transmission electron microscopy (TEM), and micro-Raman measurements. Panchromatic CL imaging of bulk STO revealed contrast features associated with growth-related striations, extended defects, and mechanical damage. CL imaging of undoped high-resistivity substrates was limited by beam charging effects. The weak nature of the CL signal from epitaxial STO (relative to bulk material) made it very difficult to visualize any features by analog detection. On the other hand, spectrally resolved CL measurements of epitaxial STO using single-photon counting techniques, revealed sensitivity to the defect content and film quality across a 3-in wafer. Preliminary results indicate a qualitative correlation in the room-temperature near band-edge luminescence properties ͑3.2-3.5 eV͒ and crystalline quality as determined by micro-Raman spectroscopy and TEM.

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