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This paper describes Raman spectroscopy of microstructured silicon (Si), which is used for electronic displays, solar cells, and other applications. Enhanced Raman scattering was found for excimer laser crystallized polycrystalline Si (ELC poly-Si) thin films, texture-structured Si, black Si, and porous Si. Raman scattering of those materials reflects mainly the conditions at projections on their surfaces. Atomic force microscopy and Raman spectroscopy for ELC poly-Si indicated that hillocks and ridges are located at grain boundaries where the defect density is relatively large and the thermal stress in the films is somewhat relaxed. The enhancement effect was shown to be useful for detecting a local vibration mode that could not be easily detected for mirror-finished Si. The variation in the enhancement ratio with the incident light wavelength was examined for comparison with the electromagnetic model. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of polycrystalline binary narrow-bandgap intermetallic RuGa3 and RuIn3 compounds have been investigated in the temperature range from 373 K to 973 K. These compounds exhibit semiconductor-like transport properties with large Seebeck coefficients of -560 μV/K and 280 μV/K at 373 K for RuGa3 and RuIn3, respectively. The Seebeck coefficient of RuGa3 changed rapidly from large negative to large positive values around 500 K, which is consistent with our calculation based on the full-potential-linearized-augmented-plane-wave method. In contrast, RuIn3 is a p-type material at its operating temperature. The dimensionless figures of merit ZT of pure compounds reached maximum values of 0.13 and 0.17 at about 973 K and 773 K, respectively. The potential maximum ZT value was evaluated using the Boltzmann transport equation and can exceed unity by electron- or hole-doping for both compounds. By substituting Co for Ru in RuIn3, n-type thermoelectric materials (ZTmax = 0.10 at 473 K) were obtained. We suggest that ZT will be enhanced by further effective electron-doping. [ABSTRACT FROM AUTHOR]

Stress and defects in polycrystalline silicon (poly-Si) for thin-film transistor (TFT) were investigated on the aspect of difference of techniques between excimer laser annealing (ELA) with extremely short pulse duration and continuous-wave laser lateral crystallization (CLC). Micro-Raman spectroscopy was used for characterization. Mapping measurements with high spatial resolution were carried out for the optical-phonon mode at ∼520 cm-1 to observe distribution of stress and defects. Defects were characterized also by local-vibration modes (LVMs) in ∼2000 cm-1 region, where LVMs were induced by terminating dangling bonds at defects with hydrogen atoms. Significant tensile stress was found for both ELA and CLC, which magnitude is dominated by the thermal stress. The stress in ELA poly-Si tends to relax in the vicinity of grain boundaries. Densities of defects in grains and dangling bonds at grain boundaries in CLC poly-Si films were apparently smaller than those in ELA films. Those differences are attributed to cooling rates of ELA and CLC. The defects in CLC poly-Si distribute extending along the laser scan direction parallel to TFT channel current, which is effective to prevent the deterioration of TFT characteristics by residual defects. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have developed a frequency-domain terahertz spectrometer based on homebuilt 1 μm band external cavity diode lasers, for high resolution spectroscopy. Our spectrometer is digitally controlled to a resolution of 10 MHz, and uses InGaAs/GaAs photoconductive antennas. We have obtained a spectrum in the range 0.02 THz to 2.5 THz, which exceeds the conventional temperature tuning range of a distributed feedback diode laser. We achieved a signal-to-noise ratio of up to 80 dB at around 0.05 THz, and 20 dB at around 2.0 THz. We observed water vapor spectra in the atmosphere with a frequency step of 0.6 GHz in the region between 1.0 THz and 2.0 THz. We have demonstrated that our 1 μm-band frequency-domain terahertz spectrometer is competitive when compared with existing 800 nm- and 1.5 μm-band systems. [ABSTRACT FROM AUTHOR]

The maximum dimensionless figure of merit, ZTmax, as a function of the chemical potential of the narrow-bandgap intermetallic compound RuGa2 was calculated by using the Boltzmann transport equation with a simple rigid band approach under the constant relaxation time assumption. The calculation, including the effect of the group velocity, indicates that ZTmax over unity would be achieved by electron doping rather than hole doping. Based on this calculation, the effects of Ir substitution for Ru on the thermoelectric properties for RuGa2 have been investigated in the temperature range from 373 K to 973 K. Indeed, a relatively large ZT value of 0.31 for n-type material was obtained in the nominal composition of Ir3.0Ru30.4Ga66.6. The discussion includes the validity of the rigid band approximation and further enhancement of ZT from theoretical and experimental aspects. [ABSTRACT FROM AUTHOR]

This letter describes the relationship between electron mobility and Si-hydrogen bonding configurations in poly-Si thin films after plasma-hydrogenation treatment. A 50-nm-thick amorphous-Si film was crystallized by excimer laser irradiation followed by plasma hydrogenation. Measurements of the Hall effect and Raman scattering demonstrated that mobility increased under the Si-H dominant state and decreased under the Si-H[sub 2] dominant state, which were respectively caused by adjusted and excessive hydrogenation times. Mobility degradation was recovered by dissociation of excess H atoms by annealing. The origin of the correlation is discussed in terms of imperfections such as grain boundaries and in-grain defects.© 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]