分子束外延Zn_（1－x）Cd_xSe／ZnSe超晶格的拉曼光谱

运用分子束外延（ＭＢＥ）技术成功地生长出Ｚｎ１－ｘＣｄｘＳｅ／ＺｎＳｅ超晶格，并对不同的样品进行了拉曼散射光谱的测试。获得了多达５级的ＺｎＳｅ的ＬＯ声子峰和ＺｎＳｅ的ＴＯ声子峰；同时还在频移为１４４ｃｍ－１、３７０ｃｍ－１处观测到了两个新声子峰，估计是来自于ＺｎＣｄＳｅ的声学模和光学模。     

Resonant Raman study of LO + acoustic phonon modes in CdSe

In studying resonant Raman scattering in the vicinity of the A and B excitons of CdSe, we have observed three new Raman peaks. Two of the peaks have been identified as two-phonon modes consisting of a longitudinal optical (LO) phonon plus respectively a transverse acoustic (TA) and a longitudinal acoustic (LA) phonon. A theory which involves the scattering of photoexcited B excitons to the A exciton by acoustic phonons via the piezoelectric exciton-phonon interaction was found to explain quantitatively the peak positions, lineshape and resonance enhancements of the observed peaks.     

Multiphonon resonant Raman scattering in N‐doped ZnO

Multiphonon resonant Raman scattering in N‐doped ZnO films was studied, and an enhancement of the resonant Raman scattering process as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed at room temperature. The resonant Raman scattering intensity of the 1LO phonon in N‐doped ZnO appears three times as strong as that of undoped ZnO, which mainly arises from the defect‐induced Raman scattering caused by N‐doping. The nature of the 1LO phonon at 578 cm⁻¹ is interpreted as a quasimode with mixed A₁ and E₁ symmetry because of the defects formed in the ZnO lattice. In addition, the previously neglected impurity‐induced two‐LO‐phonon scattering process was clearly observed in N‐doped ZnO. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of the LO phonon energy by using electronic and optical methods in AlGaN/GaN

The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.     

GaAs/AlAs超晶格的近共振喇曼散射研究

本文介绍GaAs/AlAs超晶格的室温近共振喇曼散射测量结果。由于超晶格中Fr?hlich相互作用的共振增强效应,GaAs LO声子偶模的散射得到了很大的增强。和前人的结果一样,在偏振谱我们观察到了偶模。但和前人的结果不同,在退偏振谱中我们观察到的是奇模,而不是偶模。从而证明了在近共振条件下LO声子限制模仍遵从与非共振时一样的选择定则。二级喇曼散射实验结果表明,在偏振谱中二级谱是由两个偶模组合而成,而在退偏振谱中的二级谱与前人的结果不同,由一个奇模与一个偶模组合而成。上述结果与最近提出的黄朱模型的预言是一 关键词：     

ZnSe/ZnCdSe超晶格的共振拉曼散射特性

ＺｎＳｅ／ＺｎＣｄＳｅ超晶格的共振拉曼散射特性李文深池元斌＊李岩梅＊范希武申德振杨宝均王敬伯（中国科学院长春物理研究所，激发态物理开放实验室长春１３００２１）＊（吉林大学超硬材料国家重点实验室，长春１３００２３）ＲｅｓｏｎａｎｔＲａｍａｎＳｐｅｃｔｒ...     

Exciton-phonon coupling in indirect gap AgBr nanocrystals

The resonance Raman scattering observed in the exciton region of indirect AgBr nanocrystals with mean particle radius R ≈ 5 nm is analyzed. Considering the processes as absorption followed by emission and calculating the size dependent exciton energies by the donor-like exciton model of Ekimov et al. [1], the 1TO(L) and 2TO(L)&LO(Γ) resonance behavior can be well-reproduced. The analysis of the Raman spectral lineshape based on linear exciton-phonon coupling shows a substantial increase of coupling strength with excitation photon energy. It is attributed to enhanced acoustic and surface phonon interaction of higher exciton states.     

Zn0.76Cd0.24Se/ZnSe多量子阱的共振喇曼光谱

本文报道了在Zn0.76Cd0.24Se/ZnSe多量子阱(MQWs)中,用不同的Ar+激光线激发,观察到了共振增强的喇曼散射。首次在室温和77K的条件下,用Ar+的457.9nm谱线激发,观察到分别来自ZnSe垒层和Zn0.76Cd0.24Se阱层的限制纵光学声子模(LO)的喇曼散射,并对上述不同的光学模的起因进行了分析。     

Wave vector conservation in the first order resonant Raman scattering

The dependence of the shape and the intensity of the first order resonant Raman line 1LO on the direction and magnitude of phonon wave vector has been investigated in CdS crystals. Comparison of RRS in different orientations shows that in the most pure samples the phonon wave vector is determined, to a great extent, by the momentum conservation law. In Ni doped crystals one can observe violation of momentum conservation, resulting in a sharp increase of 1 LO intensity. The shape of the 1 LO line in such sample does not depend on the experimental orientation. For the first time the dependence of the Raman intensity on the scattering angle has been observed by the comparison of forward and backward scattering spectra. Observation of this dependence shows that the free excitons are the dominating intermediate states in the resonant Raman scattering in A₂B₆ compounds.     

分子束外延ZnSe/GaAs材料的拉曼散射研究

用分子束外延(MBE)技术，在GaAa(100)衬底上生长了厚度从0．045μm到1．4μm的ZnSe薄膜。通过室温拉曼光谱的测量对ZnSe薄膜纵光学声子(Longitudinal-opticalphonon)的谱形进行了分析。用拉曼散射的空间相关模型定量分析了一级拉曼散射的型间相关长度与晶体质量之间的关系，结果表明ZnSe外延层的晶体质量随着外延层厚度的减薄是渐渐退化的，这是由于界面失配位错引入外延层所致，理论分析与实验结果相吻合。     

Photoluminescence and resonant Raman scattering in N-doped ZnO thin films

A combination of studies on photoluminescence and resonant Raman scattering in N-doped ZnO thin films were carried out at room temperature. In the photoluminescence spectra, a transformation of radiative recombination mechanism from free-exciton to donor-acceptor-pair transition was observed. An enhancement of resonant Raman scattering processes as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed in the Raman spectra. Also, the nature of the 1LO phonon underwent a transformation from a pure A₁(LO) mode to a quasimode with mixed A₁ and E₁ symmetry. The underlying mechanisms accounting for the influences of N doping on the optical properties of ZnO were related to the incorporation of extrinsic defects in the crystal lattice.     

ZnSe-ZnS应变超晶格的Raman散射

本文报导了Znse—ZnS应变超晶格的Raman光学声子谱.我们观测到,随着应变大小的改变,ZnSe和ZnS的纵向光学声子发生频移.ZnSe层中纵向光学声子可发生较大的蓝移,也可发生较小的红移;ZnS层中的纵向光学声子发生较大的红移.这些现象为“应变场下的光学模理论”所解释.文中还报导了在波数为110cm-1处观测到一很强的散射峰,并把它归结为超晶格表面层单斜Se所引起的散射;在其它地方还观测到非晶态Se、三角Se引起的散射峰.     

静压下(CdTe)_2(ZnTe)_4-ZnTe多量子阱结构的多声子共振拉曼散射

用加静高压的方法改变光学能隙来实现共振条件。在以(CdTe)_2(ZnTe)_4短周期超晶格为阱层,(ZnTe)_(4)为垒层的多量子阱结构中观察到高达四阶的类 ZnTe 纵光学声子模的多声子共振拉曼散射。通过对拉曼位移随压力变化的分析,发现在与(CdTe)_2(ZnTe)_4短周期超晶格共振时测得的类ZnTe 纵光学声子模的频率比与 ZnTe 势垒层共振时测得的 ZnTe 纵光学声子模的频率低4cm~(-1)。并将它归结为在短周期超品格中纵光学声子模的限制效应。在与短周期超品格严格的2LO 声子出射共振条件下观察到了类 CdTe 的2LO 声子的共振拉曼峰。     

Coherent optical phonon oscillations in bulk GaN excited by far below the band gap photons

We report on generation of coherent optical phonon oscillations in 150 microm thick bulk GaN. With photon energy far below the band gap, the generation mechanisms of coherent phonon modes of A1(LO), high- and low-frequency E2 are revealed to be the impulsive stimulated Raman scattering. We find that one among the two degenerate E2 modes is selectively detected with a proper choice of probe polarization. Dephasing times range from 1.5 to 70 ps for different modes, and phonon-three-photon absorbed carrier interactions are compared between the A1(LO) and the E2 mode.     

Chemical composition of matrix-embedded ternary II–VI nanocrystals derived from first- and second-order Raman spectra

A one- and multiphonon Raman scattering study is performed for an extensive set of CdS_1–xSe_x, Cd_1–yZn_yS, Cd_1–yZn_ySe, and CdSe_1–xTe_x nanocrystals to investigate the applicability of first- and second-order Raman spectra for the determination of the matrix-embedded ternary nanocrystal composition. For one-mode ternary systems both the LO and 2LO phonon frequencies in the Raman spectra are shown to be a good measure of the nanocrystal composition. For two-mode systems, the approaches based on the difference of the LO phonon frequencies (first-order Raman spectra) or double LO overtone and combination tone frequencies (second-order Raman spectra) as well as on the LO phonon band intensity ratios are analysed. The weak electron–phonon coupling in the II–VI nanocrystals and the polaron constant values for the nanocrystal sublattices are discussed.     

N型4H-SiC低温拉曼光谱特性

利用拉曼散射技术对N型4H-SiC单晶材料进行了30～300 K温度范围的光谱测量。实验结果表明,随着温度的升高,N型4H-SiC单晶材料的拉曼峰峰位向低波数方向移动,峰宽逐渐增宽。分析认为,晶格振动随着温度的升高而随之加剧,其振动恢复力会逐渐减小,使振动频率降低;原子相对运动会随温度的升高而加剧,使得原子之间及晶胞之间的相互作用减弱,致使声学模和光学模皆出现红移现象。随着温度的升高,峰宽逐渐增宽。这是由于随着温度的升高声子数逐渐增加,增加的声子进一步增加了散射概率,从而降低了声子的平均寿命,而声子的平均寿命与峰宽成反比,因此随着温度的升高峰宽逐渐增宽。声子模强度随温度升高呈现不同规律,E₂(LA),E₂(TA),E₁(TA)和A₁(LA)声子模随着温度升高强度单调增加,而E₂(TO),E₁(TO)和A₁(LO)声子模强度出现了先增后减的明显变化,在138 K强度出现极大值。分析认为造成原因是由于当温度高于138 K时,高能量的声子分裂成多个具有更低能量的声子所致。     

First-order Raman scattering in cylindrical wurtzite nanowire

We have presented a theoretical study on electron resonant Raman scattering (ERRS) process associated with the bulk longitudinal optical (LO), surface optical (SO) and quasi-confined (QC) phonon modes in a free-standing wurtzite nanowire (NW). We consider the Fröhlich electron–phonon interaction in the framework of the dielectric continuum model. Numerical calculations on the GaN material reveal that differential cross-section (DCS) is sensitive to the wire size. The bulk LO and high-frequency quasi-confined (QC₊) phonons make main contributions to the DCS and the impact of the SO phonon can be negligible in the ERRS process. Moreover, scattering intensity of the bulk LO phonon is strongly enhanced as the incident photon energy approaches the energy band-gap of the GaN.     

Resonant Raman effect in TlBr: Forbidden one-phonon and intervalley scattering at the direct exciton

Resonant Raman scattering at the direct exciton in TlBr at 1.8K is reported. The cross-section for forbidden 1LO (Γ) scattering shows resonances at both the 1s and 2s exciton. For the first time strongly resonant forbidden 1TO (Γ) scattering is observed for which possible mechanisms are discussed. Several two-phonon Raman processes involving M-point phonons confirm by direct observation the phonon intervalley scattering between non-equivalent X-points.     

Raman scattering in hydrogenated amorphous silicon under high pressure

The first studies on the pressure dependences of the first-order Raman spectra in plasma-deposited a-Si:H films are reported. With increasing pressure up to 25 kbar the TO optical phonon band shows a shift in peak to higher frequencies with a sharpening of width while the TA acoustic phonon band shows a shift in peak to lower frequencies with a broadening of width. The LO optical phonon band shows a shift in peak to higher frequencies whereas the LA acoustic phonon band remains unchanged. These pressure effects are discussed with changes in force constant and structural disorder. The alloying effect of H atoms on the Raman spectra is also discussed while comparing the pressure effects.     

Raman scattering from CuBr and CuI

Detailed temperature-dependent Raman spectra of CuI and CuBr are reported for the first time. Spectra have been recorded between room temperature and 6K. Peaks arising from scattering by the zone-center optic phonon modes have been identified and their frequencies compared with those determined by neutron scattering and infrared measurements. The LO phonon energy in CuBr is found to reflect the negative thermal expansion at low temperatures while the TO phonon frequency does not follow this behavior. Second-order features of the CuI spectrum are identified using available phonon dispersion curves.