Development of a Raman spectrometric system and application to characterization of ultra thin films of atomic scale

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The aim of this project is (1) to construct a system for Raman spectroscopy which provides us with high through-put and excellent rejection rate for Rayleigh light and (2) to apply the constructed system to characterization of ultra thin films of semiconductors and also materials with very small scattering efficiency. Our system consists of a notch filter and a double monochromator with high reflection mirrors.The through-put of the double monochromator is 24%, which greatly exceeds those of conventional systems. The detection limit of weak Raman signals has been evaluated actually. It was about 2cps (counts per second) when using a photomultiplier and 0.1 cps for a CCD detector.Using the constructed system we have characterized thin epitaxial films of semiconductors and silicon on insulators. Furthermore, phase transition of C_<60> crystals and electronic Raman scattering of doped SiC crystals have been studied.We could measure the Raman spectra of ZnTe and GaSb films with thicknesses down to 2nm. Residual stress and quality of the films have been characterized from the thickness dependence of the Raman spectra.The crystallinity of GaAs films grown at low temperatures has also been evaluated.Conversion from amorphous state to crystalline state by thermal annealing has been studied by measuring the two-dimensional Raman image of silicon on insulator (SOI) structures.Our system has enabled us to measure the Raman spectra of C_<60> crystals at lower laser powers below a critical power producing photo-induced structural change.