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

本项目的目的是：(1)构建一个具有高通量和优异瑞利光抑制率的拉曼光谱系统；(2)将构建的系统应用于半导体超薄膜和散射效率极低的材料的表征。我们的系统由陷波滤光片和带高反射镜的双单色器组成。双单色仪的通量为24%，大大超过了传统的系统。对弱拉曼信号的检测极限进行了实际评估。使用光电倍增管时约为2ps（每秒计数），而使用CCD检测器时约为0.1 cps。利用所构建的系统，我们表征了半导体和硅在绝缘体上的外延薄膜。此外，还研究了C_<60>晶体的相变和掺杂SiC晶体的电子拉曼散射。我们可以测量厚度低至2nm的ZnTe和GaSb薄膜的拉曼光谱。利用拉曼光谱的厚度依赖性表征了薄膜的残余应力和质量。本文还对低温生长的砷化镓薄膜的结晶度进行了评价。通过测量绝缘体上硅（SOI）结构的二维拉曼图像，研究了非晶态到晶态的热退火转化过程。我们的系统使我们能够在较低的激光功率下测量C_<60>晶体的拉曼光谱，低于产生光致结构变化的临界功率。

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.