Second-Order Raman Scattering from n- and p-Type 4H-SiC

The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm-1 with energy difference about 10cm-1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm-1 of the second-order Raman is not the overtone of the A1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.

Raman Investigatins of 3C-SiC Films Grown on Si (100) and Sapphire (0001) by LPCVD

The Raman measurements have been performed with the back-scattering geometry on the SiC films grown on Si(100) and sapphire (0001) by LPCVD. Typical TO and LO phonon peaks of 3C-SiC were observed for all the samples grown on Si and apphire substrates, indicating the epilayers are 3C-SiC polytype. Using a free-standing 3C-SiC film removed from Si(100) as a free-stress sample, the stresses of 3C-SiC on Si(100) and sapphire (0001) were estimated according to the shift of TO and LO phonons.

a-SiN_x∶H薄膜退火前后微结构的Raman谱研究

于2010-11-23批量导入

随激发波长改变的SiC纳米棒的Raman光谱

用不同波长的激光激发得到了SiC纳米棒的Raman光谱，发现谱的形貌与体材料有很大差别，并且随着激发光的改变出现明显变化，认为是由于受Frohlich相互作用影响而引起的共振现象，并据此对实验结果进行了解释。

镶嵌在氧化硅薄膜中纳米硅的Raman散射研究

系统研究了a-SiO_x的Raman散射谱及其退火行为,并通过退火技术使Si从SiO_x网络中分凝出来,形成纳米硅和SiO_2的镶嵌结构。并利用Raman散射技术研究了这种复合薄膜中纳米硅的声子态。发现在100～600cm~(-1)的波数范围内，纳米硅的Raman谱可用5条Lorentz线得到很好地拟合，并对这5条线的来源作了确认；观测到了在600～1 100cm~(-1)范围内纳米硅的双声子散射。研究结果表明，镶嵌在SiO_2介质中的纳米硅具有非晶硅相和纳米硅晶相共存的特点，两者均对Raman散射有贡献。不仅观测到了声子限制效应使一级光学声子频率随纳米硅晶粒尺寸减小而红移这一现象，而且还发现(与体硅相比)声子限制效应对二级Raman散射具有增强效应，并对二极散射模的频率也会产生影响。

纳米硅薄膜的Raman光谱

通过等离子增强化学气相沉积法,制备了本征和掺磷的氢化纳米硅薄膜(nc-Si:H)，研究了晶粒尺寸和掺杂浓度对纳米硅薄膜喇曼谱的影响。结果表明晶粒变小和掺杂浓度增加都使纳晶粒的TO模峰位逐渐偏离声子限制模型的计算值。X射线衍射和高分辨电镜像的结果表明晶粒变小导致硅晶粒应力增加，而掺要使晶粒内部杂质和缺陷增多，这些因素破坏了晶粒变小导致晶粒应力增加，而掺杂使晶粒内部杂质和缺陷增多，这些因素破坏了晶粒内晶格的平移对称性进一步减小声子的平均自由程，导致实验值偏离理论计算值。晶格平称对称性的破缺还体现在，随晶粒尺寸减小或掺杂浓度增加，喇曼谱中TA、L振动模的相对散射强度增加。

Raman谱研究不同缓冲层结构对Si_(1-x)Ge_x应力弛豫的影响

应用Raman散射谱研究超高真空化学气相淀积(UHV/CVD)生长的不同结构缓冲层对恒定组分上表层Si_(1-x)Ge_x层应力弛豫的影响。Raman散射的峰位不仅与Ge组分有关,而且与其中的应力状态有关。在完全应变和完全弛豫的情况下，Si_(1-x)Ge_x层中的Si-Si振动模式相对于衬底的偏移都与Ge组分成线性关系。根据实测的Raman峰位，估算了应力弛豫。结果表明

分子束外延低温生长GaAs的Raman光谱研究

对从GaAs衬底剥离下来的低温下分子束外延生长的GaAs(LTG-GaAs)薄膜进行了喇曼光谱测量，研究了不同温度下生长的LTG-GaAs在退火前后晶体完整性的变化。首次观测到了190℃生长样品中As沉淀物所引起的喇曼峰，并证明800℃快速热退火30秒后产生的As沉淀物是无定形As。

ZnSe-ZnTe应变层超晶格的Raman光谱研究

于2010-11-23批量导入

Raman scattering and infrared absorption of silicon nanocrystals in silicon oxide matrix

Structural dependence on annealing of a-SiOx:H was studied by using infrared absorption and Raman scattering. The appearance of Raman peaks in the range of 513-519cm(-1) after 1170 degreesC annealing was interpreted as the formation nanocrystalline silicon with the sizes from 3-10nm. The Raman spectra also show the existence of amorphous-like silicon phase, which is associated with Si-Si bond re-construction at boundaries of silicon nanocrystallites. The presence of the shoulder at 980cm(-1) of Si-O-Si stretching vibration at 1085cm(-1) in infrared spectra imply that except that SiO2 phase, there is silicon sub-oxide phase in the films annealed at 1170 degreesC. This sub-oxide phase is located at the interface between Si crystallites and SiO2, and thus support the shell model for the mixed structures of Si grains and SiO2 matrix.

Observation of the resonant Raman behavior of individual single-walled carbon nanotubes

The different resonant Raman scattering process of single-walled carbon nanotubes (SWNTs) has been found between the Stokes and anti-Stokes sides of the radial breathing modes (RBMs), and this provides strong evidence that Raman spectra of some special diametric SWNTs are in resonance with their electronic transitions between the singularities in the one-dimensional electronic density of states in the valence and conduction bands, and other SWNTs axe beyond the resonant condition. Because of the coexistence of resonant and non-resonant Raman scattering processes for different diametric SWNTs, the relative intensity of each RBM does not reflect the proportion of a particular SWNT.

Effect of rapid thermal annealing on the Raman spectrum of Si0.33Ge0.67/Si (100) alloy

The effect of thermal annealing on the Raman spectrum of Si0.33Ge0.67 alloy grown on Si (100) by molecular beam epitaxy is investigated in the temperature range of 550-800 degrees C. For annealing below 700 degrees C, interdiffusion at the interface is negligible and the residual strain plays the dominant role in the Raman shift. The strain-shift coefficients for Si-Ge and Ge-Ge phonon modes are determined to be 915 +/- 215 cm(-1) and 732 +/- 117 cm(-1), respectively. For higher temperature annealing, interdiffusion is significant and strongly affects the Raman shift and the spectral shape.

Raman study on residual strains in thin 3C-SiC epitaxial layers grown on Si(001)

Raman scattering measurement has been used to study the residual strains in the thin 3C-SiC/Si(001) epilayers with a variation of film thickness from 0.1 to 1.2 mu m. which were prepared by chemical vapor deposition (CVD)growth. Two methods have been exploited to figure our the residual strains and the exact LO bands. The final analyzing results show that residual strains exist in the 3C-SiC epilayers. The average stress is 1.3010 GPa, and the relative change of the lattice constant is 1.36 parts per thousand. Our measurements also show that 3C-SiC phonons are detectable even for the samples with film thickness in the range of 0.1 to 0.2 mu m. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Electronic and vibrational Raman scattering in resonance with yellow luminescence transitions in GaN on sapphire substrate

We analyze low-temperature Raman and photoluminescence spectra of MBE-grown GaN layers on sapphire. Strong and sharp Raman peaks are observed in the low frequency region. These peaks, which are enhanced by excitation in resonance with yellow luminescence transitions, are attributed to electronic transitions related to shallow donor levels in hexagonal GaN. It is proposed that a low frequency Raman peak at 11.7 meV is caused by a pseudo-local vibration mode related to defects involved in yellow luminescence transitions. The dependence of the photoluminescence spectra on temperature gives additional information about the residual impurities in these GaN layers.