Raman characterization of local electrical properties and growth process in modulation-doped 6H-SiC crystals J. Appl. Phys. 95, 3547 (2004); 10.1063/1.1655682Raman scattering from LO phonon-plasmon coupled modes and Hall-effect in n-type silicon carbide 4H-SiC Raman spectroscopy has been used to investigate wafers of both 4H-SiC and 6H-SiC. The wafers studied were semi-insulating and n-type ͑nitrogen͒ doped with concentrations between 2.1ϫ10 18 and 1.2ϫ10 19 cm Ϫ3 . Significant coupling of the A 1 longitudinal optical ͑LO͒ phonon to the plasmon mode was observed. The position of this peak shows a direct correlation with the carrier concentration. Examination of the Raman spectra from different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data are compared with a resistivity map of the wafer. These results suggest that Raman spectroscopy of the LO phonon-plasmon mode can be used as a noninvasive, in situ diagnostic for SiC wafer production and substrate evaluation.

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26 cubic SiC (3C-Sic) films grown on (100) Si by way of chemical vapor deposition (CVD) with SiC film thicknesses ranging from 600 Å to 25 μm have been studied by photoluminescence at 2 K. The ‘‘defect-related’’ W band near 2.15 eV appears in very thin-film samples. The G band near 1.90–1.92 eV and its phonon side bands G1 and G2 are believed to be related to dislocations and extended defects. The ratio ρ of the intensities of the G band and the strongest nitrogen-bound exciton (N-BE) TO(X) line may be used as a figure of merit for crystalline perfection in CVD 3C-SiC films. General formulas for the band-gap shift due to an axial stress, including three special cases—hydrostatic pressure and uniaxial and biaxial stress—are derived and applied to the CVD 3C-SiC/Si system. An experimental relationship of stress in these epitaxial films of 3C-SiC as a function of depth is obtained. It is shown that a 1–3 μm transition layer greatly reduces the interface misfit strain. For films thicker than 3 μm the film stress decreases slightly with increase of film thickness. The effects of biaxial stress on the relative intensities of N-BE lines are experimentally studied. It is reported that biaxial stress in the SiC/Si system depresses the intensity of the no-phonon line as well as the TA, LA, and LO phonon transitions of the N-BE spectrum.

Negative differential resistance associated with hot phonons J. Appl. Phys. 112, 063707 (2012) Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method J. Appl. Phys. 112, 063109 (2012) Optical properties of InGaPN epilayer with low nitrogen content grown by molecular beam epitaxy J. Appl. Phys. 112, 063507 (2012) Residual compressive stress induced infrared-absorption frequency shift of hexagonal boron nitride in cubic boron nitride films prepared by plasma-enhanced chemical vapor deposition J. Appl. Phys. 112, 053502 (2012) Spontaneous emission and optical gain characteristics of blue InGaAlN/InGaN quantum well structures with reduced internal fieldWe present the results of optical studies of the properties of In x Ga 1Ϫx N epitaxial layers (0Ͻx Ͻ0.2) grown by metalorganic chemical vapor deposition. The effects of alloying on the fundamental band gap of In x Ga 1Ϫx N were investigated using a variety of spectroscopic techniques. The fundamental band-gap energies of the In x Ga 1Ϫx N alloys were determined using photomodulation spectroscopy measurements and the variation of the fundamental band gap was measured as a function of temperature. The effects of pressure on the band gap for In x Ga 1Ϫx N samples with different alloy concentrations were examined by studying the shift of photoluminescence ͑PL͒ emission lines using the diamond-anvil pressure-cell technique. The results show that PL originates from effective-mass conduction-band states. Anomalous temperature dependence of the PL peak shift and linewidth as well as the Stokes shift between photoreflectance and PL lines is explained by composition fluctuations in as-grown InGaN alloys.

Electron field emission from SiC/Si heterostructures synthesized by carbon implantation using a metal vapor vacuum arc ion source A set of formulas for Raman shifts of diamond and zinc-blende semiconductors under a generalized axial stress are derived. The Raman shifts under hydrostatic pressure, uniaxial and biaxial stresses are only the special cases of the general formulas. Raman-stress coefficients and mode parameters are introduced, by which the Raman shifts due to different kinds of applied stresses are related. By the analysis of known Raman data of cubic SiC (3C-SiC) under hydrostatic pressures, one of the Raman-stress coefficients is obtained and the existing elastic stiffness constants of 3C-SiC are optimized. Unreliable data in the literature are pointed out and a choice of the best available data is made (C, I = 5.4, C," = 1.8, and C 44 ,= 2.5 X 10 12 dynl cm 2 ). A series of chemical-vapor-deposited .3C-SiC films on (100) Si with the film thicknesses between 4 and 17 ft.lm are measured by Raman scattering. We propose a method for calculating the stress and strain in these SiC films. The stresses in 3C-SiC en Si are in the range of 0.3-1.1 GPa and strains are on the order of 0.1 %-0.2%, which is a factor of 100 below the lattice mismatch between bulk 3C-SiC and Si. Further discussion of the release of strain due to misfit dislocations and the effect of the buffer layer on the film stress is given. Our expressions and the method of the measurement of the stress and strain in heterostructures are quite general and may be used for other systems. 6827

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Development and application of laser-based diagnostic and therapeutic procedures have been hindered by the current technical inadequacies in tissue diagnosis and characterization. It is now possible to apply the techniques of Raman spectroscopy to achieve rapid, noninvasive, and nondestructive differentiation of diseased from normal tissues. Normal and diseased breast tissues were examined by Raman spectroscopy. The Raman spectra obtained contain features that are attributable to various amounts of carotenoids and lipids. A small contribution from a heme-type signal was detected in some samples of clinically abnormal yet histopathologically benign breast tissue, while a much stronger heme-type signal was detected in most of the breast cancers. Raman spectra of diseased breast tissue (benign and malignant) also show markedly diminished to absent contributions from lipids and reduced contributions from carotenoids. This laser-based spectroscopic modality is readily adaptable to reflected light microscopy and optical fiber techniques, making it potentially useful as an aid in real-time diagnosis, and may thus find application in the fields of histopathology and interventional radiology.

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